CN115740792A - Method for generating high-stability supercontinuum light source based on solid sheet - Google Patents

Abstract

The invention discloses a method for generating a high-stability supercontinuum light source based on a solid sheet, as follows: S1: placing at least one solid sheet on a two-dimensional or multi-dimensional micro-displacement platform; S2: converging an ultrashort laser pulse into the incident solid sheet After a certain irradiated area on the front surface, nonlinear optical effects are generated during the propagation process in the solid sheet to realize spectral broadening; S3: At the same time, the optical power probe is used to sample and detect the ultrashort laser pulses after interacting with the solid sheet to realize Real-time measurement and recording of the power of the sampling beam; S4: Based on the detected power value, calculate the change range of the real-time power relative to the initial power, thereby obtaining a quantitative assessment of the aging of the solid sheet; S5: The main control system issues control commands The micro-displacement platform is controlled to move according to the preset movement mode to realize the continuous update of the irradiation area of the solid sheet, thereby realizing the ultrashort pulse light source that generates a high-stability supercontinuum.

Description

A method for generating a highly stable supercontinuum light source based on solid flakes

technical field

The invention relates to the technical field of ultrashort laser pulses, and more specifically, to a method for generating a high-stability supercontinuum light source based on a solid sheet.

Background technique

For the field of ultrashort laser pulses, realizing shorter pulse time width has always been the focus and difficulty of the development of the field. From the time-bandwidth product relationship of the Fourier transform limit pulse, it can be seen that to obtain a shorter pulse time width, a wider spectral bandwidth must be supported. Usually, under the premise of maintaining high coherence of different spectral components, the spectral bandwidth of laser pulses can be significantly broadened through certain technical methods, and then the pulse dispersion compensation can be performed through certain technical methods to achieve significant compression of the ultrashort laser pulse time width. That is, how to extend the spectral bandwidth of ultrashort pulses as coherently as possible is the core technical issue for obtaining narrower time widths of ultrashort pulses. Generally speaking, since the gain bandwidth of the laser gain medium is relatively fixed, the limit pulse width of the ultrashort laser pulse based on the specific laser gain medium is basically the same. But in fact, the energy of ultrashort laser pulses needs to be significantly amplified at the cost of sacrificing the time width of the pulses. For example, in the chirped pulse amplification technology, when the chirped ultrashort laser pulse is amplified by high-intensity pumping in the laser crystal, there will be a significant narrowing of the gain bandwidth, which will lead to the limit of the high-energy ultrashort pulse output by the ultrashort laser amplifier. The width should be significantly larger than the limit width of the small energy ultrashort pulse output by the ultrashort laser oscillator. For example, the limit pulse width of a titanium (Ti) sapphire ultrashort pulse oscillator can be less than 10 fs, while the limit pulse width of a Ti sapphire ultrashort pulse amplifier is generally greater than 20 fs. In addition, ytterbium-doped (Yb) crystals have a much narrower gain bandwidth than Ti:sapphire crystals, making it difficult to obtain pulse widths below 100 fs for ultrashort laser pulses based on ytterbium-doped crystals. Therefore, whether it is for Ti:Sapphire ultrashort pulse laser or Ytterbium-doped ultrashort pulse laser, in order to obtain a few-period high-energy ultrashort pulse laser output for these two mainstream ultrashort pulse lasers, it is necessary to further target the pulse outside the laser cavity. Significant coherent broadening of the spectral bandwidth, followed by temporal compression to obtain extremely narrow, even close to single-period, pulse time widths.

At present, the spectral broadening of ultrashort pulses is mainly based on the third-order nonlinear effects induced by strong ultrashort pulses in transparent media, especially the induced optical Kerr effect (such as self-phase modulation and cross-phase modulation) to cause pulse spectral broadening. . Typically, a strong ultrashort pulse transmitted in a transparent solid medium can achieve a significant broadening of the ultrashort pulse spectrum, thereby forming a supercontinuum output. For example, in the 1980s, researchers have used bulk fused silica to achieve significant spectral broadening of ultrashort pulses, compressing the pulse time width from 100fs to 20fs. However, although there have been related research follow-ups for a long period of time later, this technology has not been widely used, especially in commercial applications.

On the one hand, this is because the transparent solid medium has a high third-order nonlinear coefficient, and its self-focusing threshold is small. When the spectrum of high-energy ultrashort pulses is broadened, it is easy to induce self-focusing to form a multi-filament transmission state, which eventually leads to laser transverse Disturbance of the mode and optical damage of the transparent medium. Therefore, when using a transparent solid medium for ultrashort pulse spectrum broadening, it is necessary to control the laser spot size incident on the surface of the medium according to the energy of the laser pulse, and to select an appropriate medium thickness, so that the influence of self-focusing is not enough to destroy the transmission mode of the beam feature. That is to say, there is a strong competitive relationship between wide spectral broadening and good output mode. It is very difficult to balance the relationship between the two to obtain a good spectral broadening effect-this needs to be based on the characteristics of each sample (or even each sample) Careful experimentation is carried out to obtain suitable laser radiation conditions, and this technology does not have practical application conditions for non-professional researchers.

On the other hand, a more serious problem is that long-term high-energy ultrashort pulse radiation will cause significant material aging in transparent solid media: strong laser radiation will cause the dielectric material to greatly enhance the absorption of laser light due to the increase in defects, At the same time, it will also lead to the appearance of transverse mode instability such as mitosis and mitosis, and these phenomena will form positive feedback (incubation effect) with the increase of radiation time and become more and more significant, making the pulse spectrum broadening significantly reduced, The beam mode deteriorates, the energy is significantly reduced, and with the incubation effect, permanent optical damage gradually occurs inside the medium, and even the surface is severely ablated due to heat accumulation. The material aging phenomenon caused by this strong laser radiation is strengthened as the pulse radiation power density approaches the laser damage threshold of the material, that is, as the pulse energy increases, the transparent solid medium ages more rapidly and permanent optical damage occurs sooner. However, the degree of spectral broadening of the pulse is significantly positively correlated with the radiation power density of the pulse. In order to pursue wider spectral broadening, the radiation power density must approach the material destruction threshold. Therefore, for the conventional spectral broadening technology based on transparent solid media, the high performance of spectral broadening and the long-term high stability of output are incompatible: to obtain excellent spectral broadening characteristics, it is necessary to sacrifice the service life of the material At the expense, this is the most important obstacle hindering the popularization and application of this technology, especially the commercial application.

Due to the above-mentioned problems in the ultrashort pulse spectrum broadening technology based on bulk solid media, this technology has not shown a clear application prospect, so it has not received much attention in the field for a long time. In recent years, an ultrashort pulse spectrum broadening technology based on solid thin slices (thin slice groups) has rekindled researchers' enthusiasm for research on solid medium spectrum broadening technology. Different from the method based on the bulk solid medium, this method based on the solid sheet group adopts multiple sheets of wide-bandgap transparent dielectric sheets (such as fused silica sheets) with a thickness of about 0.1 mm to be placed at a certain distance near the focal point of the ultrashort pulse to achieve ultra-short pulses. The short pulse interacts with the strong-field nonlinear optics of the solid flake group to achieve spectral broadening. Unlike bulk solids, solid flakes can separate the process of spectral broadening from the process of self-focusing into filaments (including multimitosis), so that the interaction of ultrashort pulses with thin flakes only induces significant spectral broadening without causing self-focusing Filtration and multimitosis: Spectral broadening mainly comes from the self-phase and cross-phase modulation caused by the optical Kerr effect in the time domain. Under the condition of high enough radiation power density, the ultrashort pulse incident on the dielectric sheet does not need to go through the self-focusing process. It can directly produce strong self-phase and cross-phase modulation to induce significant broadening of the spectrum; while self-focusing comes from the spatial distribution of medium refractive index changes caused by the optical Kerr effect in the airspace, and requires accumulation of a certain operating distance to produce significant effects. Therefore, when the thickness of the thin sheet is small enough, ultrashort pulses passing through the thin sheet can produce significant spectral broadening without significant self-focusing and filamentation effects. In addition to avoiding the problems caused by the self-focusing effect, the spectral broadening technology of the solid sheet group also provides a richer and more flexible adjustment dimension than bulk transparent media. For example, when a single solid sheet is not enough to produce sufficient spectral broadening, the cumulative spectral broadening effect can be produced by placing multiple solid sheets at specific intervals near the laser focus, and finally a broadband supercontinuum can be formed, which can be extended over time. After the domain is compressed, the ultrashort pulse output of period level can be obtained.

The above-mentioned remarkable advantages of the solid sheet (sheet group) spectral broadening technology have aroused extensive interest of researchers in related fields. In recent years, the development of more related research and the presentation of results have not only promoted the understanding of the interaction between ultrashort pulses and solid sheets, but also revealed some shortcomings of this technology. Among them, it is notable that although the solid sheet technology realizes the separation of spectral broadening and filamentation process, the thin sheet solid medium and the bulk solid medium are essentially the same matrix material, so the two are irradiated by the same strong ultrashort pulse. It has similar aging characteristics, that is, the above-mentioned aging problem that the bulk solid medium system needs to face will also be encountered in the thin solid medium system, which is an important technical problem that cannot be avoided by the solid medium thin slice spectral broadening technology. In fact, compared with bulk solids, ultrashort pulse transmission through solid sheets corresponds to a shorter nonlinear action distance, so when using solid sheets for spectral broadening, a higher pulse radiation power density needs to be applied to obtain significant spectral broadening. Therefore, to obtain a similar spectral broadening effect, thin-sheet media need to withstand stronger radiation than bulk solid media, and thus age faster during the irradiation process. For the ultrashort laser pulse spectrum broadening technology based on solid sheets, the continuous and rapid aging of materials under high radiation power density will have an important adverse effect on the stability of the output supercontinuum, such as causing supercontinuum The output power continues to decrease, the spectral broadening width continues to narrow, and the fundamental transverse mode characteristics of the output beam gradually deteriorate.

In short, the continuous and rapid aging characteristics of dielectric materials under strong ultrashort pulse radiation is an inherent technical problem that cannot be avoided for the actual long-term stable industrial application based on solid sheet (sheet group) spectral broadening technology. In order to hinder the direct technical bottleneck of the commercial application of this technology, a new technology breakthrough is urgently needed.

Contents of the invention

In order to solve the problem of material aging caused by strong laser radiation in the existing solid sheet supercontinuum technology, the present invention provides a method for generating a high-stability supercontinuum light source based on solid sheet.

For realizing above-mentioned object of the present invention, the technical scheme that adopts is as follows:

A method for producing a high-stability supercontinuum light source based on a solid sheet, the steps of the method are as follows:

S1: Place at least one solid thin slice on a two-dimensional or multi-dimensional micro-displacement platform;

S2: After the ultrashort laser pulse is converged into a certain irradiation area on the front surface of the solid sheet, nonlinear optical effects are generated during the propagation process in the solid sheet to achieve spectral broadening;

S3: At the same time, the optical power probe is used to sample and detect the ultrashort laser pulse after interacting with the solid sheet, so as to realize the real-time measurement and recording of the sampling beam power;

S4: Based on the detected power value, calculate the change range of the real-time power relative to the initial power, thereby obtaining a quantitative assessment of the aging of the solid sheet;

S5: The main control system sends out control instructions to control the micro-displacement platform to move according to the preset movement mode to realize continuous updating of the irradiation area of the solid sheet, thereby realizing the ultrashort pulse light source that generates a high-stability supercontinuum.

The beneficial effects of the present invention are as follows:

In the process of ultrashort pulse irradiating solid thin slices to produce supercontinuum, long-term high-intensity ultrashort laser pulse irradiation will cause significant aging phenomena in solid thin slice dielectrics: strong light irradiation induces random generation of lattice defects and The non-uniform change of the refractive index, which leads to the significant enhancement of the laser absorption of the material, also easily leads to the phenomenon of laser filamentation, and with the increase of the intense laser irradiation time, these phenomena become more and more significant due to the incubation effect, and then in the solid sheet medium The internal or surface causes permanent optical damage, and even causes severe ablation damage on the surface of the medium due to heat accumulation caused by absorption. The continuous aging of the transparent dielectric material caused by the above-mentioned strong light irradiation will significantly reduce the spectral broadening of the supercontinuum generated by the ultrashort pulse irradiation of the solid sheet, deteriorate the beam transverse mode mode, and significantly reduce the pulse energy, thus greatly hindering Long-term high-stable operation of supercontinuum light source based on solid sheet technology. The method of the present invention aims at the above-mentioned technical problems of the solid sheet supercontinuum source, and obtains a quantitative evaluation of the aging of the solid sheet by real-time monitoring of the beam power variation range during the process of irradiating the solid sheet with ultrashort laser pulses to generate the supercontinuum, and based on This evaluation controls the movement of the solid sheet according to the preset movement mode, and realizes the continuous update of the irradiation area of the solid sheet during the long-term irradiation of the strong laser, thus effectively avoiding the time and space of the aging process of the medium material in the irradiation area. Continuously accumulate to create suitable material and physical conditions for the long-term stable output of supercontinuum. That is to say, the present invention real-time and quantitatively evaluates the aging of solid thin slices irradiated by strong ultra-short laser pulses, and introduces automatic control technology to realize the continuous update of the thin slice irradiation area, effectively avoiding severe aging of the dielectric material in the irradiation area, thereby extremely Greatly reduce the impact of material aging on power stability, spectral broadening, and transverse mode characteristics during supercontinuum generation, and finally achieve long-term high-stability output of supercontinuum light sources based on solid sheet technology.

Description of drawings

Fig. 1 is a flow chart of the method for producing a solid sheet-based high-stability supercontinuum light source according to the present invention.

Fig. 2 is a schematic diagram of an optical path of the method for generating a high-stability supercontinuum light source according to the present invention.

Fig. 3 is another optical path schematic diagram of the method for generating a high-stability supercontinuum light source according to the present invention.

Figure 4 shows three preset motion modes for updating the ultrashort pulse irradiation area on a solid sheet.

Fig. 5 is a kind of trajectory of updating the ultrashort pulse irradiation area on the square solid sheet.

Fig. 6 is another trajectory of updating the ultrashort pulse irradiation area on a square solid sheet.

Fig. 7 is another movement trajectory for updating the ultrashort pulse irradiation area on a square solid sheet.

Fig. 8 is a kind of trajectory of updating the ultrashort pulse irradiation area on the circular solid slice.

Fig. 9 is another motion trajectory for updating the ultrashort pulse irradiation area on a circular solid sheet.

In the figure, 1-femtosecond laser; 2-continuous attenuation film; 3-variable diaphragm; 4-plano-convex lens; 5-solid sheet; 6-optical power probe; 7-main control system; 8-micro-displacement platform; 9- Beam splitter.

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

Example 1

For the supercontinuum generation technology based on ultrashort laser pulse irradiation of solid thin slices (flake groups), the continuous aging of dielectric materials under high laser irradiation intensity will have an important adverse effect on the stability of the supercontinuum output. , such as the continuous decline in output power, the continuous narrowing of spectral broadening, and the continuous deterioration of the transverse mode characteristics of the output beam. That is to say, the inevitable aging of dielectric materials caused by strong laser irradiation is an important reason that hinders the long-term and stable industrial application of this supercontinuum generation technology. The present invention revolves around the inherent problem of solid sheet supercontinuum technology, and proposes a method for generating a high-stability supercontinuum light source based on solid sheet, as shown in Figure 1, specifically as follows:

S1: Place at least one solid thin slice on a two-dimensional or multi-dimensional micro-displacement platform;

S2: After the ultrashort laser pulse is converged into a certain irradiation area on the front surface of the solid sheet, nonlinear optical effects are generated during the propagation process in the solid sheet to achieve spectral broadening;

S3: At the same time, the optical power probe is used to sample and detect the ultrashort laser pulse after interacting with the solid sheet, so as to realize the real-time measurement and recording of the sampling beam power;

S4: Based on the detected power value, calculate the change range of the real-time power relative to the initial power, thereby obtaining a quantitative assessment of the aging of the solid sheet;

S5: The main control system sends out control instructions to control the micro-displacement platform to move according to the preset movement mode to realize continuous updating of the irradiation area of the solid sheet, thereby realizing the ultrashort pulse light source that generates a high-stability supercontinuum.

In a specific embodiment, as shown in FIG. 2 , the ultrashort laser pulse output by the femtosecond laser 1 sequentially passes through the continuous attenuation sheet 2 for controlling the single pulse energy of the ultrashort laser pulse, and for controlling the incident ultrashort laser pulse. The variable diaphragm 3 of the diameter of the laser pulse beam and the plano-convex lens 4 used for focusing are converged, and then enter a certain irradiation area on the front surface of the solid sheet 5 . The irradiated light intensity generated by the ultrashort laser pulse on the surface of the solid sheet 5 can cause the incident ultrashort laser pulse to have a significant nonlinear optical interaction with the solid sheet 5, and at the same time make the aging time constant of the solid sheet 5 in "hours". Time Scale. In the present embodiment, the ultrashort laser pulse output by the femtosecond laser 1 is converged by the plano-convex lens 4 and then irradiated on the front surface of the solid sheet 5. The resulting radiation intensity can make the incident ultrashort laser pulse and the solid sheet produce significant nonlinear optics. Specifically, the central wavelength of the femtosecond laser 1 used in this embodiment is 800nm, the pulse width is 50fs, the repetition frequency is 1KHz, the beam diameter is 8.5mm (1/e ² width), and the polarization is linear polarization along the horizontal direction . The solid sheet 5 used is a quartz glass sheet whose front and rear surfaces are optically polished, its thickness is 0.1mm, and the size of the square transparent surface is 10mm×10mm. Among them, the ultrashort laser pulse output by the femtosecond laser can be controlled by the single pulse energy through the continuous attenuation plate 2, and its beam transverse mode with Gaussian distribution can be further controlled by the variable diaphragm 3 placed in the center relative to the laser beam , and the follow-up convergence operation should be realized by selecting a plano-convex lens 4 with an appropriate focal length according to the irradiation conditions generated by the supercontinuum. In general, the beam diameter of the focused spot of a collimated beam is proportional to the focal length of the converging lens and inversely proportional to the incident beam diameter. Therefore, by adjusting the continuous attenuation sheet 2 to control the energy of the incident ultrashort pulse single pulse, adjusting the iris 3 to control the diameter of the incident ultrashort pulse beam, and selecting plano-convex lenses 4 with different focal lengths, the instantaneous light irradiated on the solid sheet 5 The intensity can be flexibly controlled, so as to obtain the suitable conditions for ultrashort laser pulses to irradiate solid thin slices to produce supercontinuum: convergent ultrashort laser pulses can produce strong nonlinear optical interactions with solid thin slices to significantly broaden their own spectra, while their irradiation The intensity will not lead to rapid laser-induced damage to solid flakes (although the dielectric material will still produce cumulative structural changes and even ablation damage under long-term irradiation of this intensity laser).

For example, in a typical irradiation parameter setting, the iris 3 is fully opened, that is, the femtosecond laser Gaussian beam is not affected by the iris 3, and the focal length of the plano-convex lens 4 is selected as 2.0m, at this time The diameter of the waist of the converging Gaussian beam is about 0.24 mm. Under such converging conditions, typically, when the laser irradiation power is 370mW, although the ultrashort laser pulse propagates in the air, there is no self-focusing filament phenomenon, and the solid sheet 5 irradiated by the ultrashort laser pulse can produce significant The spectrum is broadened, but the irradiated area of the solid sheet 5 will rapidly undergo ablation damage at a time scale close to 1 minute (if the time interval from initial irradiation to ablation damage is defined as the aging time constant, the aging time constant is close to 1 minute). However, by adjusting the continuous attenuation sheet 2 to reduce the laser irradiation power to 250mW, the solid sheet 5 will not appear ablation damage (aging time constant greater than 1 hour) under laser irradiation on a time scale of more than 1 hour, but only accumulate The decrease of the laser transmittance caused by the structure change, that is, the decrease of the output power of the supercontinuum. Moreover, under such converging conditions, when the irradiation power is 250mW, the spectral broadening of the supercontinuum produced by ultrashort laser pulse irradiation on solid thin slices is close to saturation. Therefore, this irradiation condition can be used as a suitable condition for ultrashort laser pulse irradiating solid thin slices to produce supercontinuum.

As another example, in another typical irradiation parameter setting, let the iris 3 be adjusted to a clear aperture of 2 mm, and the focal length of the plano-convex lens 4 is selected to be 0.10 m. The diameter is about 0.10mm. Under such converging conditions, typically, when the laser irradiation power is 68mW, ultrashort laser pulse irradiation of the solid sheet 5 can produce significant spectral broadening, but the irradiated area of the solid sheet 5 will be on a time scale close to 1 minute. Ablative damage occurs rapidly (aging time constant approaching 1 minute). However, by adjusting the continuous attenuation sheet 2 to reduce the laser irradiation power to 46mW, the solid sheet 5 will not appear ablation damage (aging time constant greater than 1 hour) under laser irradiation on a time scale of more than 1 hour, but only accumulate The decrease in transmittance caused by structural changes, that is, the decrease in supercontinuum output power. Moreover, when the irradiation power is 46mW under such converging conditions, the spectral broadening of the supercontinuum produced by ultrashort laser pulse irradiation on quartz thin slices is also close to saturation. Therefore, this irradiation condition can also be used as a suitable condition for ultrashort laser pulse irradiating solid thin slices to produce supercontinuum.

In a specific embodiment, in step S1, a solid thin slice 5 is placed on the two-dimensional micro-displacement platform 8 to achieve the purpose of the system continuously and automatically updating the laser irradiation area during the long-term irradiation of the strong laser on the thin slice. In this embodiment, the displacement range of the two-dimensional micro-displacement platform 8 or the multi-dimensional micro-displacement platform should be able to cover the entire light-transmitting surface of the solid sheet 5, and the displacement path of the two-dimensional or multi-dimensional micro-displacement platform can be preset And stored in the main control system, so that the ultrashort laser pulse scanning irradiation on the solid sheet 5 according to the set path can be realized. On the other hand, since the sampling and detection of the ultrashort laser pulse after interacting with the solid sheet 5 in this embodiment is realized by directly detecting the power of the reflected laser beam after interacting with the solid sheet 5, the surface method of the solid sheet 5 The line needs to form a non-zero angle with the incident ultrashort laser pulse transmission direction, so that the reflected ultrashort laser pulse beam and the incident ultrashort laser pulse beam can be spatially separated, and then the reflected ultrashort laser pulse beam can be realized. Detection of beams. In fact, generally, the laser irradiation condition of the solid sheet 5 is set to Brewster's angle, so as to minimize the reflection loss of the solid sheet 5 . Comprehensively considering the requirements of sampling power and the above-mentioned anti-reflection requirements, in this embodiment, the angle between the surface normal of the solid sheet 5 and the transmission direction of the incident light is set to be close to the Brewster's angle, not the Brewster's angle, To reserve the appropriate reflected light power for sampling monitoring. Under this laser incident angle setting, in order to ensure that the spatial position of the laser irradiation sheet in the beam propagation direction is unchanged when the solid sheet 5 is updated to a new irradiation area (so that the laser irradiation light of the solid sheet 5 is updated after the irradiation area strong consistency), the direction of the two mutually vertical displacement axes of the micro-displacement platform with two-dimensional translation function should be set to be in the light-transmitting surface of the solid sheet 5, and in this embodiment along the horizontal direction (horizontal axis) and the vertical axis respectively. vertical direction (vertical or y-axis) to match laser polarization conditions along the horizontal direction. For the solid sheet 5 with a square light-transmitting surface in this embodiment, when it is placed on the micro-displacement platform, the ideal placement plan to meet the above requirements is to make the two sides of the solid sheet 5 perpendicular to each other along the two sides of the micro-displacement platform. The direction of displacement is vertical, so that the subsequent update operation of the irradiated area can make full use of the light-transmitting area of the solid sheet 5 . Then, the operation of adjusting the incident angle of the laser on the solid sheet 5 is realized by directly rotating the micro-displacement platform along the y-axis.

The two-dimensional micro-displacement platform in this embodiment can also be extended to a three-dimensional micro-displacement platform. For a three-dimensional micro-displacement platform, typically, its three two-by-two mutual vertical displacement axis directions can be set to be along the incident light transmission direction (z axis), and along the horizontal direction (x axis) in the plane perpendicular to the incident light transmission direction. ) and the vertical direction (y-axis). Under the condition of having three-dimensional motion capability, the micro-displacement platform can move through one-axis, two-axis or three-axis to ensure that when the solid sheet 5 placed arbitrarily on the micro-displacement platform updates the irradiation area, the laser irradiates the sheet in the beam propagation direction The spatial position of the two-dimensional micro-displacement platform remains unchanged, without considering the above-mentioned special direction correlation requirements between the two when the solid sheet is placed on the two-dimensional micro-displacement platform, so the solid sheet has greater adjustment flexibility. For example, the operation of adjusting the incident angle of the laser by the solid sheet 5 placed on the three-dimensional micro-displacement platform 8 can be realized by keeping the micro-displacement platform fixed and rotating the solid sheet along the y-axis.

A solid sheet 5 in this embodiment can also be expanded into a solid sheet group, that is, in addition to placing a solid sheet 5 near the focal point of the ultrashort laser pulse, two solid sheets can also be placed at a certain interval near the focal point of the ultrashort laser pulse. One or more solid thin slices to achieve two-level or multi-level spectral broadening of solid thin slices irradiated by ultrashort laser pulses, thereby greatly improving the spectral broadening capability of solid thin slice spectral broadening technology. For the situation of this solid sheet group, there are two typical forms of setting the micro-displacement platform: one is that all the solid sheets are placed on the same micro-displacement platform, that is, all the solid sheets update the position of the radiation area at the same time; The second is that each solid sheet is placed on a micro-displacement platform, so that the irradiated area of each solid sheet can be individually updated by separately monitoring the aging of each sheet.

In a specific embodiment, in step S2, the high-energy ultrashort laser pulse propagates in the solid sheet 5 and generates spectral broadening due to nonlinear optical effects, forming a supercontinuum ultrashort pulse output. Specifically, after the ultrashort laser pulse is incident on a certain irradiation area on the front surface of the solid sheet 5, it will propagate in the medium of the solid sheet. As mentioned above, by adjusting the continuous attenuation plate 2 and the iris diaphragm 3, and selecting the plano-convex lens 4 with different focal lengths, the instantaneous light intensity irradiated on the solid sheet 5 can be controlled in the state where the ultrashort laser pulse interacts with the solid sheet. A window of suitable irradiation conditions for the supercontinuum, such as the two typical irradiation parameter settings listed above. Under these irradiation conditions, since the laser irradiation intensity is in the physical interaction intensity window where the third-order nonlinear optical effects such as self-phase modulation, cross-phase modulation, four-wave mixing, and stimulated Raman scattering occur significantly, the incident ultrashort During the propagation process of the laser pulse in the solid sheet, the above-mentioned third-order nonlinear optical interaction with the solid sheet medium will produce a significant spectrum broadening, and form a supercontinuum ultrashort pulse output after passing through the solid sheet.

In this embodiment, the above two typical irradiation parameter settings can be used to expand the spectral bandwidth (full width at half maximum) of the ultrashort laser pulse from 30nm to 60nm after the initial interaction between the incident ultrashort laser pulse and a solid sheet, and the pulse The energy utilization rate can be close to 95%. However, under the condition of a fixed irradiation area, as the irradiation time increases, the above-mentioned spectral bandwidth expansion and pulse energy utilization rate of the output supercontinuum ultrashort pulse will gradually decrease. When the solid sheet is moved to update the irradiation area, the spectral bandwidth expansion and pulse energy utilization rate of the output supercontinuum ultrashort pulse will return to the initial value.

In a specific embodiment, in step S3, the reflected light beam generated by the convergent high-energy ultrashort laser pulse on the front and rear surfaces of the solid sheet 5 is collected by the optical power probe 6, and then transmitted to the main control system 7 after photoelectric conversion. Realize real-time measurement, recording and monitoring of reflected laser beam power. In this embodiment, it is necessary to sample and detect the high-energy ultrashort laser pulse after interacting with the solid sheet 5, so as to realize real-time measurement and monitoring of the beam power of the sampled ultrashort laser pulse. In fact, the ultrashort laser pulse irradiating the solid sheet will produce reflections on the front and rear surfaces of the solid sheet, and the reflected beam can be used as a sampling beam to monitor the change of laser power after interacting with the solid sheet 5 . That is, the sampling detection in this embodiment is realized by detecting the ultrashort laser pulse beam reflected after interacting with the solid sheet 5 .

It should be noted that the detected reflected light beams in this embodiment include the reflected light from the front surface and the back surface of the solid sheet 5 . The reflected light from the front surface reflects the reflection generated during the interaction between the incident ultrashort laser pulse and the front surface of the solid sheet, while the reflected light from the rear surface reflects the interaction process between the supercontinuum ultrashort pulse after spectral broadening and the back surface of the solid sheet Reflections generated in both will show a decrease in reflectivity due to aging or destruction of the solid sheet on the surface and inside. In the power monitoring process of the reflected light beam, the optical power probe 6 with a sufficiently large detection area can completely collect the reflected light on the front and rear surfaces, so as to ensure the stability of the measured power data during the long-term detection process and reduce the light beam The effect of jitter on data accuracy.

In this embodiment, the angle between the surface normal of the solid sheet 5 and the incident light transmission direction is set to 45 degrees, which is close to but not equal to the Brewster's angle (56 degrees) of quartz glass, so as to ensure that Under the above-mentioned typical irradiation parameter setting conditions, a suitable reflected light power can be reserved for the probe 6 to realize stable and low-noise detection.

For example, under the conditions of the above-mentioned laser incident angle and the setting of the first irradiation parameter, the incident laser with a power value of 250 mW irradiates the solid sheet 5 to produce a reflected beam power value of about 85 μW; at the above-mentioned laser incident angle and the second irradiation Under the conditions set by the parameters, the reflected beam power value generated by the incident laser with a power value of 46 mW irradiating the solid sheet 5 is about 16 μW: both reflected beam power values can ensure that the optical power probe 6 used in this embodiment is at a high level. Sensitive low noise detection interval.

In the detection setup of this embodiment, a silicon photoelectric power sensor with an effective detection area of 10 mm×10 mm is used to realize complete collection of reflected light beams. In addition, since the reflected beam is emitted by a converging beam close to the beam waist, which has divergent characteristics, the silicon photoelectric probe should be placed at an appropriate distance from the solid sheet to avoid excessively high instantaneous irradiating light intensity due to ultrashort pulses on the probe surface As a result, the detection signal has nonlinear or even saturation characteristics, or the beam divergence is too large to achieve complete acquisition. In addition, in order to avoid nonlinear or even saturation characteristics of the probe due to excessive instantaneous irradiated light intensity, the reflected ultrashort laser pulse can be attenuated by a neutral filter before the reflected ultrashort laser pulse enters the probe Then, it is incident on the probe.

For example, corresponding to the first irradiation parameter setting, the silicon photoelectric probe 6 is placed in the center relative to the reflected beam at a distance of 50 cm from the irradiation point of the solid sheet 5, and a suitable neutral filter is arranged in front of the probe to detect the incident ultrashort laser pulse. Attenuation (placing the filter close to the probe can also reduce the effect of ambient light) to avoid nonlinear characteristics of the signal detected by the probe.

The probe 6 converts the collected optical signal into an electrical signal and transmits it to the main control system 7, and then the main control system 7 records and presents the real-time collected power data, thereby realizing real-time measurement of the beam power of the reflected ultrashort laser pulse, Record and monitor.

In a specific embodiment, in step S4, the main control system 7 further calculates the real-time change range of the detected real-time power relative to the initial power based on the detected reflected laser beam power value, and obtains the ultrashort laser pulse radiance Real-time and quantitative assessment of the aging condition of the illuminated solid sheet 5. Generally speaking, with the increase of the intense ultrashort laser pulse irradiation time, the irradiated area of the solid sheet will gradually age, which will lead to the gradual increase of the material's absorption of the irradiated laser. This gradual increase in the absorption of the irradiated laser is fed back to the reflected beam, resulting in a gradual decrease in the power of the detected reflected beam, and the decrease in the reflected light is positively correlated with the increase in the absorption of the irradiated light. Therefore, by detecting the real-time decline of reflected light, the aging of solid flakes can be evaluated in real time and quantitatively.

Theoretically, the aging speed of solid thin slices is directly related to the irradiated laser light intensity, and presents a significant nonlinear evolution feature: as the irradiated laser light intensity gradually increases and approaches the single-pulse damage threshold, the aging speed of solid thin slices will increase. The faster and faster the time interval from the initial irradiation to the occurrence of ablation damage, that is, the aging time constant (Δt _d ) will be shorter and shorter. In fact, when the aging rate of the solid sheet is in a relatively fast interval (such as when Δt _d is on the "minute" time scale), the randomness of the aging process of the solid sheet will become larger (such as the uncertainty of Δt _d will increase), It is not conducive to the stable output of the supercontinuum and the closed-loop feedback control of the system. Therefore, in order to avoid various adverse effects caused by the rapid aging of solid flakes during supercontinuum generation, the intensity of laser irradiation should be controlled in a range where the aging speed of solid flakes is relatively slow in practical applications. The laser power selection corresponding to the typical irradiation parameter settings of the above two examples can make the solid sheet in the slow aging interval, and its Δt _d is on the "hour" time scale.

In a specific embodiment, in step S5, based on the evaluation of the aging condition of the solid sheet, the main control system 7 issues an instruction to control the movement of the micro-displacement platform, so that the micro-displacement platform 8 moves according to a preset mode to achieve a strong Continuous updating of the irradiated area of the thin slice during the long-term laser irradiation of the solid thin slice 5 .

In this embodiment, based on the evaluation of the aging of the solid sheet, the following preset motion control mode of the solid sheet can be adopted in this embodiment to realize the continuous position update of the irradiated area of the solid sheet, as shown in the preset motion in Figure 4 Mode 1: the main control system monitors the decline of the sampling beam power. When the beam power decline is greater than the preset first threshold, the main control system controls the micro-displacement platform to update the movement distance along the preset distance greater than the diameter of the irradiation spot. Set path movement.

Specifically, the solid sheet can be evenly divided into several irradiation regions according to the size of the solid sheet, the diameter of the irradiation spot of the ultrashort laser pulse, and the incident angle formed by the incident ultrashort laser pulse and the solid sheet; by setting the beam power The first threshold value of the drop range is used as the trigger condition for the movement of the solid sheet. When the drop range of the beam power is greater than the preset first threshold value, the main control system controls the micro-displacement platform to move accordingly, so that the radiation area of the ultrashort laser pulse is The current radiation area is switched to the adjacent radiation area to realize spatial fixed-point and time-discrete updating of the solid sheet irradiation area.

In the solid sheet motion control mode described in this embodiment, when the real-time drop of the detection laser power is greater than the preset first threshold, the main control system 7 will issue an instruction to control the movement of the micro-displacement platform 8, through the micro-displacement platform The irradiated area of the solid sheet is updated by moving the set distance according to the preset path. Specifically, the setting of the first threshold needs to focus on two factors.

First of all, the first threshold should not be set too small, because the beam power of the incident ultrashort pulse laser is not absolutely stable, it will inevitably fluctuate randomly or systematically with time, and this intrinsic beam power noise may Can cause false triggering of threshold conditions. Wherein, for the case of random noise, the measured power values statistically present a normal distribution with a specific mean power and power standard deviation. According to the characteristics of the normal distribution, the probability of 1 standard deviation is 68.26895%, the probability of 2 standard deviations is 95.44997%, the probability of 3 standard deviations is 99.73002%, the probability of 4 standard deviations is 99.99367%, and 5 times the standard deviation The probability of being bad is 99.99994%. Considering the detection duration with the "hour" time scale and the number of sampling detections on the order of a thousand, it can be known from the above data that when the first threshold is set to be equal to or greater than 4 times the standard deviation of the incident beam power, a lower laser can be obtained Probability of false triggering of power; while setting the first threshold equal to or greater than 5 standard deviations of the incident beam power ensures that triggering of the first threshold of power is almost always due to aging of the solid sheet rather than power noise of the laser cause. Therefore, in order to avoid false triggering of the first threshold condition as much as possible, the first threshold described in this embodiment is set to be equal to or greater than 5 times the standard deviation of the ultrashort pulse laser power.

Specifically, when the first threshold is set to 5 times the standard deviation of the ultrashort pulse laser power, considering a single measurement, the probability of random noise triggering the first threshold condition is only 0.00006%, less than one in a million. Considering 1000 measurements, the probability of random noise triggering the first threshold condition is only 0.06%, which is less than one in a thousand. That is, for the ultrashort laser pulse light source of the power root mean square error <0.5% (RMSE, 24-hour continuous measurement) used in this embodiment, when the first threshold set is equal to 2.5% of the power drop range, also That is, when approximately equal to 5 times the standard deviation of the laser power, the probability of the laser power noise triggering the first threshold condition is almost negligible.

In addition, in order to further reduce the noise of input laser power, especially the influence of long-term systematic fluctuation of laser power caused by environmental changes on the stability of power measurement, so as to further reduce the probability of false triggering of the first threshold condition, the The current input laser beam power is used for real-time beam split sampling detection. Based on the real-time measurement of the input laser sampling beam power W _I (t) before the action, the laser sampling power W _R (t) after the action measured in real time by the probe 6 and the initial input laser sampling power W _I (0) before the action and the real-time input The method of multiplying the ratio of W _I (t) of the laser sampling power to obtain the corrected laser sampling power: W _Rr (t) = W _R (t) W _I (0)/W _I (t), to realize the laser The power noise is eliminated to significantly reduce the influence of the input laser power noise on the measured power after the action, so that the real-time measured power after the action can more truly reflect the aging degree of the solid sheet.

On the other hand, when the probe 6 is used to detect the laser power, by increasing the sampling integration time, the influence of the short-term random noise of the laser power can also be effectively reduced, and more stable laser power data can be obtained.

Secondly, under the condition of meeting the lower limit requirements of the above threshold setting, the threshold should be set in the range near the lower limit, 1.0 to 1.5 times the lower limit, so as to avoid the super-continuity of the system output before the irradiation area is updated due to the excessive threshold Spectral characteristics (power and spectral broadening) have changed significantly. For the high-stability supercontinuum light source technology that automatically updates the irradiated area of the solid sheet in the embodiment, the stability of the supercontinuum output for a long time is determined by the set threshold. For example, if the threshold set above is greater than 2.5% of the beam power drop, the maximum drop of the supercontinuum long-term output power curve will be anchored at 2.5%, and will appear approximately periodically, reflecting systemic causes The resulting curve cycle fluctuations. That is to say, the larger the threshold setting, the greater the periodic fluctuation, and the more the supercontinuum light source deviates from the high-stable operating characteristics; the smaller the threshold setting, the smaller the periodic fluctuation, and the supercontinuum Spectrum light sources can also obtain smaller systematic deviations and achieve better high-stable operating characteristics.

Therefore, considering the above two aspects of threshold setting, the first threshold in this embodiment is directly set to the lower limit of the threshold required to almost completely avoid noise false triggering, that is, the threshold is 5 times the standard deviation of the ultrashort pulse laser power .

In this embodiment, the pre-set threshold is stored in the main control system. When the main control system monitors that the power of the probe beam has dropped more than the threshold, the main control system 7 will issue an instruction to control the movement of the micro-displacement platform 8. . The command includes the displacement movement command of one or two or three displacement axes in the two-dimensional or three-dimensional micro-displacement platform, and specifically involves the movement direction (forward or reverse) and movement distance of each displacement axis that needs to move. Based on the light-passing area of the solid sheet, the diameter of the irradiated spot, and the incident angle of the ultrashort laser pulse, the movement path of the solid sheet can be reasonably planned in advance so that the light-passing area of the solid sheet can be effectively used; the planned movement path is stored in In the main control system, the update of the ultrashort laser pulse irradiation area is implemented on the solid sheet according to the set path. Generally speaking, the distribution of laser irradiation points in the solid sheet can be set in the form of a rectangular lattice to facilitate scanning path planning.

Specifically, according to the irradiation spot size determined by the above two typical irradiation parameter settings, and the laser incident angle, the appropriate horizontal and vertical intervals between the center points of two adjacent irradiation areas can be obtained, so that the solid sheet The light passing area is fully utilized, and the rear irradiated area will not be affected by the aging of the front adjacent irradiated area. After determining the horizontal and vertical intervals of the center points of adjacent irradiation areas, the movement path of the irradiation area of the solid sheet during the long-term irradiation process can be set according to the size of the solid sheet and the laser incident angle, and each irradiation The motion parameters of each micro-displacement axis when the area is updated.

For example, for the 10mm × 10mm quartz glass used in this embodiment, when the irradiation spot diameter is 0.10mm and the incident angle is 45 degrees, it can be set to start irradiation near the point at the upper left corner of the solid sheet (such as from the left side and the points at 0.24mm and 0.20mm on the upper edge respectively), and then update the irradiation points along the horizontal direction at intervals of 0.28mm on the sheet surface (corresponding to the setting of the above-mentioned two-dimensional platform, the displacement axis in the horizontal direction moves 0.28mm; corresponding to For the setup of the above-mentioned three-dimensional platform, the x and z displacement axes move 0.20mm respectively). After scanning 35 irradiation points in the horizontal direction, the irradiation point reaches the position close to the upper right corner of the solid sheet at this time. At this time, updating the next irradiation point needs to be completed by moving down the sheet surface in the vertical direction at an interval of 0.20mm ( Corresponding to the setting of the above-mentioned two-dimensional or three-dimensional platform, the y displacement axis moves 0.20mm). Then, the updating operation of the irradiation points of the second row can be similar to the case of the first row, moving in the opposite direction until approaching the left edge of the solid sheet. At this point, move downwards at an interval of 0.20mm in the vertical direction, and the operation of updating the irradiation point will return to the situation of the first row. By repeating the above scanning operation, the light-transmitting area of the entire solid sheet will be effectively utilized, and finally 35×49=1715 irradiation points can be obtained. The schematic diagram of the moving path of the irradiation area of the above-mentioned solid sheet is shown in FIG. 5 , which is preset and stored in the main control system. In fact, if the direction of motion or the initial position of the irradiated area of the solid sheet is changed, different motion paths with the same technical effect for this embodiment can be obtained, as shown in Figures 6 and 7, there are many possibilities for the motion path , will not be listed here.

In this embodiment, after the main control system 7 issues an instruction to control the movement of the micro-displacement platform 8, the micro-displacement platform will move a specific distance according to the above-mentioned preset path, so that the irradiated area of the solid sheet is updated. For the solid sheet, if the average use time of each irradiation point is controlled to be greater than 1 hour, the total use time of this solid sheet will exceed 1715 hours, that is, the long-term high-stability output time of the supercontinuum light source can exceed 1715 hours, which is far longer than this kind of solid sheet supercontinuum light source without closed-loop control of irradiation area update and single-point irradiation. In fact, if the radiation and motion parameters remain unchanged, only the size of the solid sheet is enlarged to 30mm×30mm, that is, the effective surface area becomes 9 times the original, and the total service time of the corresponding sheet will exceed 1715×9= 15435 hours, that is, the long-term high-stability output time of the supercontinuum light source at this time can exceed 15435 hours, which can meet the service life requirements of the entire operation cycle of general light source equipment. That is, the solid sheet supercontinuum light source generated based on the method described in this embodiment does not need to replace the supercontinuum generation medium during the entire operating life cycle, thereby significantly reducing its operation and maintenance costs.

Generally, under certain irradiation parameter setting conditions, the average use time of each irradiation point above is determined by the laser irradiation power (determining the aging speed of the solid sheet, that is, the decline rate of the sampling power after the action) and the power drop threshold (determining The limit aging degree of the solid sheet, that is, the limit drop of the sampling power after the action) is determined. Therefore, when the power drop threshold is set to a fixed value, equal to 5 times the standard deviation of the ultrashort pulse laser power, the average use time of the irradiation point is only determined by the laser irradiation power. For the above two typical irradiation parameter settings in this embodiment, the laser irradiation power is set in a power range where the pulse spectrum broadening is close to saturation. In fact, in this range of laser irradiation power, the change of laser irradiation power will lead to a significant change in the aging speed (aging time constant) of the solid sheet, that is, the average service time of the irradiation point will change significantly, but the relative pulse spectrum broadens The changes are not significant. Therefore, in this embodiment, the average use time of the irradiation point that meets the above requirements can be obtained by properly adjusting the laser irradiation power in the above laser irradiation power range, and at the same time, the requirement of pulse spectrum broadening can also be taken into account.

The displacement motion mode of the two-dimensional or three-dimensional micro-displacement platform described in this embodiment is not limited to the above-mentioned translation motion mode, but also includes a rotation motion mode, or a combination of translation and rotation displacement motion modes. For example, a two-dimensional micro-displacement stage composed of a one-dimensional translation stage and a one-dimensional rotation stage can also achieve continuous position update of the solid sheet irradiation area through the combined motion of the two displacement dimensions. In particular, when the solid sheet has a circular light-transmitting surface instead of the above-mentioned square light-transmitting surface, the two-dimensional micro-translation stage composed of a one-dimensional translation stage and a one-dimensional rotation stage can make the radiation The irradiation spot forms a helical scanning line on the wafer to fully utilize the irradiation area of the circular light-transmitting surface of the solid sheet, as shown in Figures 8 and 9. That is to say, for a circular solid sheet, compared with the two-dimensional displacement method of pure translation, the two-dimensional displacement method of the combination of rotation and translation is a displacement motion method that is more suitable for the disc.

In addition, the material of the solid sheet described in this embodiment is not limited to quartz glass, but also includes various other transparent solid media applicable to supercontinuum generation, such as various common wide band gap crystals or amorphous materials. The thickness of the solid sheet described in this embodiment is not limited to 0.10 mm, and its thickness can be flexibly adjusted according to actual application requirements. The number of solid flakes described in this embodiment is not limited to one, and the number of solid flakes can be flexibly set according to actual application requirements.

Example 2

In this embodiment, in step S3, different from the sampling detection of the ultrashort laser pulse reflected after interacting with the solid sheet in the embodiment 1, this embodiment samples and detects the ultrashort laser pulse transmitted through the solid sheet after interacting with the solid sheet Perform beam split sampling detection, as shown in Figure 3. Specifically, when performing further beam splitting and sampling detection on the ultrashort laser pulse passing through the solid sheet, a beam splitter 9 for beam splitting is arranged behind the solid sheet 5 to divide the emitted ultrashort laser pulse into two parts, Part of it is output as supercontinuum ultrashort pulse, and the other part is used as sampling beam, which is collected by an optical power probe and transferred to the main control system after photoelectric conversion, so as to realize real-time measurement and monitoring of the sampling beam power of ultrashort laser pulses, and then obtain solid Flake aging.

Embodiment 1 uses the reflected beam power of the high-energy ultrashort laser pulse after interacting with the solid sheet for real-time detection and monitoring. Compared with embodiment 2, embodiment 1 can directly utilize the reflected beam of the solid sheet itself to realize the real-time monitoring of the high-energy ultrashort laser pulse beam power after interacting with the solid sheet without adding additional optical elements (embodiment 2. It is necessary to add an additional beam splitter 9) in the optical path, which is more concise and efficient in terms of optical path design; at the same time, embodiment 1 uses the solid sheet reflection beam to carry out sampling detection monitoring and will not affect the characteristics of the output supercontinuum (output power and spectrum chirp characteristics), effectively avoiding the inevitable influence on the output supercontinuum ultrashort pulse characteristics caused by the insertion of optical elements in the exit light path in embodiment 2, and has higher practicability. Therefore, it is a better choice in Embodiment 1 to use the ultrashort laser pulse reflected after interacting with the solid sheet for sampling and detection.

Example 3

Based on embodiment 1 or embodiment 2, for the preset solid sheet motion control mode adopted in step S5 of embodiment 1, this embodiment provides another preset solid sheet motion control mode, as shown in Fig. 4 Movement mode 2 shows: Specifically, the main control system controls the quasi-continuous movement of the micro-displacement platform, so that the ultrashort laser pulse performs quasi-continuous scanning on the solid sheet according to the preset scanning path, and realizes long-term irradiation of the solid sheet by strong laser During the process, the irradiated area of the sheet is continuously updated, thereby realizing the high stability output of supercontinuum ultrashort pulses.

The main control system 7 described in this embodiment quasi-continuously sends out instructions for controlling the movement of the micro-displacement platform 8 at intervals much smaller than the aging time constant, so that the micro-displacement platform 8 moves along a preset path in a specific, significantly smaller than the radiation time. The movement distance of the diameter of the irradiation spot moves quasi-continuously along the pre-set path, so that the irradiation area of the solid sheet is updated in a near-continuous scanning manner in space and time. During the movement of the platform, based on the monitoring of the real-time sampling power drop, the average movement speed of the platform (average movement speed=update movement interval/update time interval) will be regulated by the closed-loop optimization feedback of the main control system 7, so that the solid sheet Compared with the initial sampling power during the long-term irradiation process, the real-time sampling power declines steadily towards 0 or a smaller preset value, thereby improving the long-term stability of the supercontinuum ultrashort pulse output. Specifically, adjusting the average movement speed can be realized by separately adjusting the updating movement interval, or separately adjusting the updating time interval, or simultaneously adjusting the updating movement interval and the updating time interval.

Due to the preset solid sheet motion control mode described in Embodiment 1, the update of the irradiated area is triggered by the power drop threshold, so it has the characteristics of spatial fixed point and time discrete, which will cause the power curve of the supercontinuum output to show a drop by the threshold A periodic jump determined by the amplitude. In addition, since the threshold should be set to be greater than the standard deviation of the incident laser power, the periodic fluctuations that determine the stability of the supercontinuum light source will cause the output supercontinuum stability to be significantly lower than that of the incident laser stability.

In contrast, in the preset solid sheet motion control mode described in this embodiment, the update of the irradiated area is not triggered by the threshold condition, so the problem of periodic power jumps caused by the existence of the threshold in Embodiment 1 is not solved in This example will be well resolved. It can be seen from this that the irradiation area update mode of this embodiment can bring higher stability to the output supercontinuum. In fact, since the movement speed of the micro-displacement platform in this embodiment will be regulated by the closed-loop optimization feedback of the main control system 7, it can make the monitored power drop less than the second threshold, that is, the output of the supercontinuum can be obtained very High stability.

In the preset solid sheet motion control mode of this embodiment, the initial average motion speed is obtained based on the detection and evaluation of the aging of the solid sheet. Specifically, through steps S3 and S4, the data of the fixed-point irradiation power of the solid sheet changing with time can be measured, and a quantitative evaluation of the aging speed of the solid sheet can be obtained, such as a quantitative aging time constant, and then based on this evaluation, an appropriate setting can be made. The initial average movement speed of (the appropriate irradiation update movement interval and irradiation update time interval). Generally speaking, the set initial average moving speed should at least meet the time interval of the aging time constant, and the moving distance of the irradiated area is larger than the diameter of the laser irradiation spot, so as to avoid the aging accumulation of the irradiated area during the near-continuous scanning process. Too serious, even ablative damage occurs. For example, corresponding to the average use time of each irradiation point in Embodiment 1 being 1 hour (the aging time constant is greater than 1 hour), when the value of the initial average motion speed is set in this embodiment to meet the requirements of the micro-displacement platform in the time of 1 hour When quasi-continuously moving 0.28mm along the horizontal direction, that is, the initial average moving speed in the horizontal direction is set to 0.28mm/hour, this embodiment and embodiment 1 can obtain similar aging characteristics of the solid sheet in terms of irradiation effect, so the set The initial average movement speed can effectively avoid the severe aging of solid flakes.

In fact, since the quasi-continuous scanning irradiation method adopted in this embodiment (significant overlap of front and rear irradiation spot areas) is more sufficient than the interval fixed-point irradiation method adopted in Example 1 (front and rear irradiation spot areas avoid overlapping) The area covered by the scanning path can be fully utilized to obtain a larger effective irradiation area. Therefore, if the same average motion speed is adopted for the two solid sheet motion control modes, the material of this embodiment will exhibit weaker aging characteristics. That is to say, this embodiment has more advantages in making full use of the surface area of the sheet and slowing down the aging of the material.

It should be noted that in this embodiment, the solid sheet adopts a quasi-continuous motion mode rather than a true continuous motion mode. Specifically, the main control system 7 issues an instruction to control the movement of the micro-displacement platform 8 at an update time interval that is much smaller than the aging time constant, so that the micro-displacement platform 8 moves at an update interval that is much smaller than the diameter of the irradiation spot. Since the update motion interval is set to be much smaller than the diameter of the irradiation spot, and the update time interval is set to be much smaller than the aging time constant, so from the observation of the spatial scale of the irradiation spot or the time scale of the aging time constant, this kind of motion can be regarded as quasi-continuous sports.

Although the motion patterns of Embodiment 1 and this embodiment are essentially discrete motions in time and space, the relationship between the time interval of the irradiation area update and the aging time constant, and the relationship between the motion interval of the irradiation area update and the irradiation The relationship between the diameter of the spot determines that it has significantly different motion mode characteristics and irradiation effects, and finally has a significant difference in the impact on the stability of the supercontinuum output. For example, in Embodiment 1, the time interval for updating the position of the irradiation area is determined by the threshold trigger condition, and its typical value is 1 hour, and the corresponding horizontal movement distance of 0.28 mm is twice the diameter of the irradiation spot (irradiation laser 45 Under the condition of oblique incidence), this movement mode is a typical discrete movement in time and space, and the abrupt update of the irradiation area caused by it will bring significant periodic fluctuations in the supercontinuum ultrashort pulse output curve. And for the initial time interval and the initial motion interval (co-determining the initial average motion speed) of the irradiated area position update in the present embodiment, the motion parameters are set by the main control system 7 (parameters pass through steps S3 and S4 to determine the aging condition of the solid sheet) Evaluation (obtained) decision: typically, when the update time interval is set to 45 seconds and the initial motion distance is 0.0035mm, this embodiment can not only obtain the average motion speed (0.28mm/hour) consistent with Embodiment 1, but also obtain Approximate quasi-continuous motion patterns. Because the time interval (45 seconds) is much smaller than the aging time constant (greater than 1 hour), and the movement distance (0.0035mm) is also much smaller than the irradiation spot diameter (0.10mm). This quasi-continuous motion mode in this embodiment enables the material aging characteristics of the irradiated area to extend uniformly and slowly along the motion path, avoiding the sudden change in material properties during the renewal process of the irradiated area in Embodiment 1, and thus more favorable Obtain long-term high-stability output of supercontinuum.

In this embodiment, the solid sheet adopts the quasi-continuous motion mode instead of the continuous motion mode. On the one hand, it is beneficial to reduce the operating load of the micro-displacement platform and the control system, and on the other hand, it is also beneficial to the real-time processing and closed-loop control of the feedback signal in the closed-loop control process. The timing is stable. First of all, for the micro-displacement platform based on the stepping motor used in this embodiment, compared with the long-term continuous operation, the periodic intermittent operation is more conducive to the long-term stable operation of the stepping motor of the platform. For example, for the aforementioned quasi-continuous motion with a time interval of 45 seconds and a motion distance of 0.0035 mm, the stepping motor micro-translation stage in this embodiment can continuously run 7 steps within 1 second with a step of 0.0005 mm. 0.0035mm motion spacing. That is, in the irradiated area update time interval of 45 seconds, the micro-displacement platform is in the running state only for less than 1 second, and the micro-displacement platform is in a static state for more than 44 seconds, so the platform step can be significantly reduced The heating problem caused by the continuous operation of the motor for a long time can improve its working stability and life. On the other hand, since the control module of the micro-displacement platform is in the standby state most of the time, the operating load of the system control program in the quasi-continuous motion mode is also low, and it is easy to realize the real-time processing of the feedback signal by the control program in the closed-loop control process, and to ensure The timing stability of the closed-loop control process.

The average moving speed parameter in this embodiment is an important parameter to determine the output power of the supercontinuum source and the stability of spectrum broadening. Theoretically, if the average movement speed of solid flakes is too slow and the laser irradiation flux per unit area is too high, it will lead to excessive aging of materials and affect the output quality and stability of supercontinuum; if the average movement of solid flakes If the speed is too fast and the irradiated area is updated too fast, it will cause the solid sheet to be scanned in a short period of time and need to be replaced, shortening its service life. As mentioned above, the initial average moving speed in this embodiment is obtained from the time-varying data of fixed-point irradiation power by detecting and evaluating the aging condition of the solid sheet. This detection evaluation can ensure that the initial average motion velocity is in a relatively appropriate range, and provide a parameter basis for the initial operation of the system. Then, during the quasi-continuous movement of the micro-displacement platform, based on the monitoring of the power drop, the average movement speed of the platform will be further regulated by the closed-loop optimization feedback of the main control system 7, so that the power of the solid sheet during long-term irradiation The decline rate is stable towards 0 or a small preset value. If the power decline gradually increases or maintains a larger value, it indicates that the aging of the material is aggravated or more serious, that is, the update of the irradiation area is too slow, so the main control system 7 will increase the average speed of the displacement platform (at the time interval of keeping the update) Under the same condition, it can be realized by increasing the update motion interval, or by reducing the time interval under the condition that the update motion interval remains unchanged), so as to speed up the update of the solid sheet irradiation area and reduce the power drop to close to 0 or a smaller preset value. Through this closed-loop optimization feedback regulation, the supercontinuum source based on solid sheet can obtain stable output for a long time, and its stability can be close to the level of input ultrashort pulse laser.

Furthermore, if the initial average motion speed is directly set so that the aging degree (power drop) of the solid sheet during the near-continuous scanning process is in a slight range, for example, the drop of the real-time laser power compared with the initial laser power is less than 1 times the ultrashort pulse The standard deviation of the laser power, at this time, the influence of sheet aging on the power stability and spectral broadening characteristics of the output supercontinuum ultrashort pulse is almost negligible, and the noise of the output supercontinuum ultrashort pulse is mainly caused by the noise of the input ultrashort pulse decision, thus obtaining a stability close to that of an input ultrashort laser pulse, and a spectral broadening close to that of a flake under initial irradiation. In fact, under the conditions of near-continuous scanning and weak irradiation aging, the supercontinuum ultrashort pulse output with high stability can be obtained without implementing the above-mentioned closed-loop optimization feedback regulation.

Under the same laser irradiation parameter setting, the motion path of this embodiment can be completely implemented according to the motion path of Embodiment 1. Therefore, under the condition of the same average motion speed, the same area of solid sheet has the same service life for the two motion modes. That is to say, for this embodiment, a 30mm×30mm solid sheet can also obtain a service life of more than 15435 hours, which can realize the replacement of the supercontinuum generation material during the whole operating life cycle of the system.

Example 4

For the preset solid sheet motion control mode adopted in step S5 in embodiment 1 or embodiment 3, this embodiment provides another preset solid sheet motion control mode, as shown in preset motion mode 3 in FIG. 4 : Specifically, the main control system controls the micro-displacement platform to move continuously along the preset path, so that the ultra-short laser pulse continuously scans the solid sheet according to the preset scanning path, and realizes the long-term irradiation of the strong laser on the solid sheet. The irradiated area of the sheet is continuously updated, thereby realizing the high stability output of supercontinuum ultrashort pulses.

In Embodiment 3, in step S5, the solid sheet adopts a quasi-continuous motion mode instead of a true continuous motion mode. As described in Embodiment 3, this motion mode matches the motion characteristics of the displacement platform based on the stepper motor in Embodiment 3 (even if the stepper motor runs continuously, its motion is still discrete in nature), and it is also conducive to closed-loop optimization feedback Implementation of regulation. In fact, if a micro-displacement platform with continuous displacement capability is used, such as a micro-displacement platform based on technologies such as linear motors, voice coil motors, and piezoelectric actuators, the solid sheet placed on the micro-displacement platform can achieve true continuous motion. , so as to realize the continuous scanning irradiation of ultrashort laser pulses on the solid sheet in space and time. In this embodiment, by replacing the stepper motor-based micro-displacement platform in Embodiment 3 with a linear motor-based micro-displacement platform, the main control system 7 can control the micro-displacement platform 8 to move continuously according to a preset path, so that The ultrashort laser pulse continuously scans the solid sheet along the preset scanning path to realize the continuous update of the irradiated area of the sheet, and then realize the high stability output of the supercontinuum ultrashort pulse.

In this embodiment, in step S5, the solid sheet maintains a constant movement speed during the long-term continuous movement, and performs continuous and uniform movement according to a preset path. That is to say, during the long-term movement of the sheet, the adjustment of the movement speed is not realized through closed-loop optimization feedback regulation. Compared with Embodiment 1 and Embodiment 3, the motion control mode of the solid sheet in this embodiment is simpler, and its motion characteristics are completely determined by the motion parameters initially set, rather than relying on feedback control. The equipment and technical requirements of the control modules in the system are significantly reduced.

On the other hand, since the closed-loop feedback control is not implemented during the long-time irradiation of ultrashort pulses, the aging degree of the solid sheet in this example during the long-time irradiation is completely determined by the micro-displacement Determined by the platform motion parameters. Therefore, it is particularly important for this embodiment to obtain suitable motion parameters of the micro-displacement platform. Similar to Example 3, the moving speed of the solid sheet in this embodiment is obtained based on the detection and evaluation of the aging of the solid sheet: through steps S3 and S4, the data of the fixed-point irradiation power of the solid sheet changing with time can be measured, and the information about the solid sheet can be obtained. Quantitative evaluation of the aging speed of the slice, such as obtaining a quantitative aging time constant, and then setting an appropriate movement speed based on the evaluation. Generally speaking, the set movement speed should at least meet the time interval of the aging time constant, and the movement distance of the irradiation area is greater than the diameter of the laser irradiation spot, so as to avoid excessive aging accumulation of the irradiation area during continuous scanning. Even ablative damage occurs. For example, according to the evaluation of the aging situation of the solid sheet in Embodiment 1 and Embodiment 3, the motion speed of the micro-displacement platform is set to be 0.28mm/hour in this embodiment (consistent with the average motion speed of Embodiment 1 and Embodiment 3) , when the irradiation parameter setting and motion path are consistent with Example 3, this example can effectively avoid the serious aging of the solid sheet, and obtain the radiation aging characteristics of the solid sheet similar to Example 3 and the supercontinuity Spectral ultrashort pulse output characteristics. In fact, the continuous motion mode adopted in this embodiment can completely avoid the radiation characteristic jump (even if the jump range is small) that still exists in the quasi-continuous motion mode of embodiment 3 when the irradiation area is updated, so theoretically It can eliminate the tiny system noise of the supercontinuum output power brought by the quasi-continuous motion mode mentioned above.

In this embodiment, further increasing the moving speed on the basis of the above-mentioned moving speed can keep the aging degree (power drop) of the solid sheet in a more slight range during the continuous scanning process. For example, similar to the case of weak irradiation aging in Example 3, a higher motion speed is set to make the real-time laser power drop less than 1 times the standard deviation of the ultrashort pulse laser power compared to the initial laser power. The influence of supercontinuum ultrashort pulse power stability and spectral broadening characteristics is almost negligible, and the noise of the output supercontinuum ultrashort pulse is mainly determined by the noise of the input ultrashort pulse, so it can be obtained close to the input ultrashort laser pulse stability, and close to the spectral broadening of the flakes under initial irradiation. It is worth noting that increasing the motion speed of the solid sheet needs to be at the cost of sacrificing the service life of the solid sheet. Therefore, in practical applications, the advantages and disadvantages of the two aspects can be weighed to set an appropriate motion speed. Appropriate application economy and service life can be obtained while meeting the technical requirements of the characteristics.

Under the same laser irradiation parameter setting, the motion path of this embodiment can also be completely implemented according to the motion path of Embodiment 1. Therefore, under the condition of similar motion speed to that of Embodiment 1 and Embodiment 3, this embodiment can also obtain a service life of more than 10,000 hours by using a 30mm×30mm solid sheet, and realize the full operation life cycle of the system. No replacement of materials.

Apparently, the above-mentioned embodiments of the present invention are only examples for clearly illustrating the present invention, rather than limiting the implementation of the present invention. All modifications, equivalent replacements and improvements made within the spirit and principles of the present invention shall be included within the protection scope of the claims of the present invention.

Claims (10)

1. A method for generating a high-stability supercontinuum light source based on a solid sheet is characterized in that: the method comprises the following steps:

s1: placing at least one solid sheet on a two-dimensional or multi-dimensional micrometric displacement platform;

s2: after the ultra-short laser pulse is converged and enters a certain irradiation area on the front surface of the solid slice, the non-linear optical effect is generated in the propagation process in the solid slice to realize the spectrum broadening;

s3: meanwhile, sampling detection is carried out on the ultrashort laser pulse acted with the solid sheet by adopting an optical power probe, so that real-time measurement and recording of the power of a sampling beam are realized;

s4: calculating the variation amplitude of the real-time power relative to the initial power based on the detected power value, thereby obtaining a quantitative evaluation of the aging condition of the solid sheets;

s5: the main control system sends out a control instruction to control the micro-displacement platform to move according to a preset movement mode, so that the continuous updating of the solid sheet irradiation area is realized, and the ultra-short pulse light source with high stability and ultra-continuous spectrum is realized.

2. The method for generating a high-stability supercontinuum light source based on solid flakes according to claim 1, characterized in that: after the ultrashort laser pulse is converged sequentially through an attenuation sheet for controlling the single pulse energy of the ultrashort laser pulse, a diaphragm for controlling the beam diameter of the incident ultrashort laser pulse and a converging lens for focusing the beam, the ultrashort laser pulse is incident to a certain irradiation area on the front surface of the solid slice;

the irradiation light intensity of the ultrashort laser pulse generated on the surface of the solid sheet can enable the incident ultrashort laser pulse and the solid sheet to generate obvious nonlinear optical effect, and meanwhile, the aging time constant of the solid sheet can be in the 'hour' time scale;

the aging time constant is the time length from the beginning of irradiation to the occurrence of ablation damage of the solid sheet under the fixed-point irradiation condition.

3. The method for generating a high-stability supercontinuum light source based on solid flakes according to claim 1, characterized in that: the displacement motion mode of the two-dimensional or multi-dimensional micro-displacement platform is a translation motion mode, or a rotation motion mode, or a combination of the translation motion mode and the rotation motion mode;

the displacement range of the two-dimensional or multi-dimensional micro-displacement platform can cover the whole light-passing surface of the solid sheet;

the displacement path of the two-dimensional or multi-dimensional micro-displacement platform can be preset and stored in the master control system, so that the updating of the ultrashort laser pulse irradiation area of the solid sheet according to the set path can be realized;

the displacement path is planned based on the clear area of the solid slice, the diameter of an irradiation light spot and the incident angle of an ultrashort laser pulse, so that the clear area of the solid slice is effectively utilized.

4. The method for generating a high-stability supercontinuum light source based on solid flakes according to claim 1, wherein: s3, sampling and detecting the ultrashort laser pulse acted with the solid sheet, wherein the ultrashort laser pulse can be detected by the ultrashort laser pulse beam reflected after the ultrashort laser pulse acts with the solid sheet;

the reflected ultrashort laser pulse beams comprise an ultrashort laser pulse beam reflected by the front surface of the solid sheet and an ultrashort laser pulse beam reflected by the back surface of the solid sheet;

the surface normal of the solid sheet and the transmission direction of the incident ultrashort laser pulse light beam form an included angle of not 0 degree, so that the reflected ultrashort laser pulse light beam and the incident ultrashort laser pulse light beam are separated spatially, and the reflected ultrashort laser pulse light beam can be detected.

5. The method for generating a high-stability supercontinuum light source based on solid flakes according to claim 1, wherein: s3, sampling and detecting the ultrashort laser pulse acted with the solid sheet, or performing beam splitting sampling and detecting on the ultrashort laser pulse acted with the solid sheet and penetrating through the solid sheet;

the beam splitting sampling detection is characterized in that a beam splitting sheet for beam splitting is arranged behind a solid sheet, and the ultrashort laser pulse penetrating through the solid sheet is divided into two parts, wherein one part is output as a supercontinuum ultrashort pulse, and the other part is used as a sampling beam to be detected through an optical power probe.

6. The method for generating a high-stability supercontinuum light source based on solid flakes according to claim 1, wherein: in step S5, the preset motion mode may be: the master control system monitors the descending amplitude of the power of the sampling light beam, and when the descending amplitude of the power of the light beam is larger than a preset first threshold value, the master control system controls the micro-displacement platform to move along a preset path at an updating movement interval larger than the diameter of the irradiation light spot.

7. The method for generating a high-stability supercontinuum light source based on solid flakes according to claim 1, characterized in that: in step S5, the preset motion mode may also be: and the master control system sends out an instruction for controlling the micro-displacement platform to move according to the updating time interval which is less than the aging time constant, so that the micro-displacement platform moves along a preset path according to the updating movement interval which is less than the diameter of the irradiation light spot.

8. The method for generating a high-stability supercontinuum light source based on solid flakes according to claim 1, characterized in that: step S5, the preset motion mode may further be: the main control system controls the micro-displacement platform to continuously move at a constant speed along a preset path at a constant movement speed, namely, the micro-displacement platform realizes continuous movement in space and time;

the moving speed is obtained based on the detection and evaluation of the aging condition of the solid sheet, and the value of the moving speed at least meets the time interval of an aging time constant, and the moving distance of an irradiation area is larger than the diameter of an irradiation light spot, so that ablation damage caused by the fact that the irradiation area is aged and accumulated too severely in the continuous scanning process is avoided.

9. The method for generating a high-stability supercontinuum light source based on solid flakes according to claim 6, characterized in that: in order to effectively avoid the false triggering of the first threshold condition caused by the laser power noise, the first threshold is set to be equal to or larger than the standard deviation of the ultra-short laser pulse power of N times;

in order to further reduce the probability of false triggering of the first threshold condition caused by laser power noise, the input laser beam before acting with the solid sheet is subjected to real-time beam splitting sampling detection, and laser power noise cancellation is realized by a method of multiplying real-time measured power after acting with the ratio of initial input power before acting and real-time input power.

10. The method for generating a high-stability supercontinuum light source based on solid flakes according to claim 7, characterized in that: based on monitoring of the descending amplitude of the real-time sampling power, the average movement speed of the micro-displacement platform can be regulated and controlled by closed-loop optimization feedback of the main control system, so that the descending amplitude of the real-time sampling power of the solid sheet is smaller than a second threshold value relative to the initial sampling power in the long-time irradiation process;

the average movement speed = update movement interval/update time interval, so that the average movement speed can be adjusted by adjusting the update movement interval alone, the update time interval alone, or both the update movement interval and the update time interval.

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