CN114156727B - High-power middle-infrared tunable femtosecond laser generation device - Google Patents
High-power middle-infrared tunable femtosecond laser generation device Download PDFInfo
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- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
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- H01S3/106—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling devices placed within the cavity
- H01S3/108—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling devices placed within the cavity using non-linear optical devices, e.g. exhibiting Brillouin or Raman scattering
- H01S3/1083—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling devices placed within the cavity using non-linear optical devices, e.g. exhibiting Brillouin or Raman scattering using parametric generation
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- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/005—Optical devices external to the laser cavity, specially adapted for lasers, e.g. for homogenisation of the beam or for manipulating laser pulses, e.g. pulse shaping
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Abstract
The application belongs to the technical field of infrared femtosecond laser, and discloses a high-power middle-infrared tunable femtosecond laser generating device, which comprises: the pumping module is used for pumping the OPO optical parametric oscillation module; an Optical Parametric Oscillation (OPO) module for converting an input laser (pump light) into two lower frequency output lights (signal light and idler light); and the Difference Frequency Generation (DFG) module is used for carrying out difference frequency on the two laser beams generated by the OPO module to generate high-power middle-infrared tunable femtosecond laser. The application adopts the OPO+DFG combined mode to obtain high-power mid-infrared tunable femtosecond laser, utilizes a high-power femtosecond oscillator to pump the OPO to generate tunable signal light and idler frequency light, and respectively uses the tunable signal light and the idler frequency light as pump light and signal light required by difference frequency generation to be injected into a mid-infrared nonlinear crystal to obtain the high-power femtosecond laser, so that the output mid-infrared femtosecond laser has the characteristics of high power and tunability.
Description
Technical Field
The invention belongs to the technical field of infrared femtosecond laser, and particularly relates to a high-power middle-infrared tunable femtosecond laser generating device.
Background
At present: the mid-infrared is located in the spectral wavelength range of 3-20 μm, wherein the absorption characteristic of the 3-5 μm mid-infrared laser in the atmosphere makes the band laser have important application value in the fields of military, medical treatment, remote sensing, communication, industrial processing and the like, and many research works are spreading around the mid-infrared wavelength laser in recent years. Furthermore, the middle infrared ultrashort pulse laser can reach the femtosecond level due to the extremely short pulse width, and after amplification, the pulse peak power is extremely high, so that the light source requirements of various applications such as free space optical communication, trace gas detection, environmental monitoring and biomedicine can be met. Therefore, the method has very important value for researching the mid-infrared femtosecond laser with the characteristics of wide tuning, high power and the like.
In the visible and near infrared bands, resonant cavity mode locking technology is generally adopted for realizing ultra-short pulse laser output, but due to lack of a proper laser gain medium, the tuning range of output light is narrow, and the ultra-short pulse laser output is difficult to directly apply to the mid-infrared region. For this purpose, a high-power femtosecond laser is used to obtain a high-power mid-infrared femtosecond laser with a wide wavelength tuning range by using a nonlinear frequency conversion technology. The generation of ultra-short mid-infrared laser pulses mainly utilizes nonlinear frequency conversion technology to down-convert visible ultra-short pulse frequencies into mid-infrared regions, such as Optical Parametric Oscillation (OPO) and Difference Frequency Generation (DFG). The OPO method originates in the beginning of the 60 s of the 20 th century and is to excite one laser (pump light) in a nonlinear medium to generate two laser (signal light and idler light) outputs. OPO has the characteristics of simple structure, wide tuning range, pulse, continuous mode, mode locking and other operation modes. Different resonant cavities, nonlinear crystals and pump light wavelengths are adopted to obtain laser with wide wavelength tuning range, and meanwhile, the laser has the advantages of high repetition frequency, high conversion efficiency, full solidification and the like. The DFG method is characterized in that two laser beams (pump light and signal light) are excited in a nonlinear medium to generate one laser beam (idler light) to be output, a resonant cavity is not needed in the frequency conversion process, and the laser beam passes through a nonlinear crystal once, so that the DFG method has the comprehensive advantages of no threshold limit, no need of complex cavity type adjustment, wide output laser tuning range, high efficiency and the like.
The current mature high-power femtosecond laser is a Kerr lens mode-locked laser based on titanium-doped sapphire and an all-solid-state femtosecond laser based on ytterbium-doped (Yb 3+) gain medium, and the average power output from a mode-locked oscillator of the titanium-doped sapphire laser is lower due to the fact that the titanium-doped sapphire laser is limited by the existing pump source power and the quantum efficiency of a crystal. In contrast, ytterbium-doped femtosecond lasers have higher power and good light sources, with greater advantages for outputs requiring high average power, narrow pulses. It is conceivable to directly pump the OPO with a high-power femtosecond laser to generate the femtosecond laser, or to split the pump source laser into two output beams, wherein one beam is spectrally broadened and then is subjected to difference frequency with the other beam to generate the femtosecond laser. However, both of these methods require nonlinear crystals with high transmission for 1 μm pump light, but in the existing crystals, if the transmission is high for 1 μm, the wavelength of the long wave generated by multiphoton absorption is limited to 4-5 μm, and high-power laser with longer wavelength cannot be directly generated. If a birefringent crystal such as AgGaS 2、AgGaSe2、cdSiP2、ZnGeP2 is used to generate laser light with a wavelength of 5 μm or more, the nonlinear coefficient and the quality factor of the former two are low, and the light transmission range of the crystal CbSiP 2 with a high quality factor and a large nonlinear coefficient is small (0.65-7 μm), so that high-power mid-infrared wavelength femtosecond laser cannot be obtained due to the influence of the crystal property.
The ZnGeP 2 crystal has a series of advantages of large nonlinear coefficient, high quality factor, high thermal conductivity, large damage threshold value and the like, and meanwhile, the light transmission range is wide, so that the ZnGeP 2 crystal is an excellent nonlinear optical crystal material capable of generating high-power tunable middle infrared output through a DFG process. However, a key problem with ZGP crystals is that they are opaque in the wavelength band below 2 μm and cannot be pumped by high power 1 μm near infrared lasers, but it is presently best to achieve a minimum absorption of 0.08cm -1 at 1.6 μm. Therefore, the OPO technology can be utilized to convert the 1 μm pump source laser to generate two long-wavelength femtosecond lasers of 1.7 μm and 2.6 μm, the wavelength range of the two long-wavelength femtosecond lasers is tunable, and then the ZGP crystal with excellent optical property is utilized to generate high-power mid-infrared tunable femtosecond laser in a difference frequency mode, wherein the wavelength tuning range of the high-power mid-infrared tunable femtosecond laser is 4-9 μm. The maximum advantage of the difference frequency of the nonlinear process is that near infrared signal light and idler frequency light generated by OPO are utilized to remove the difference frequency, so that the conversion efficiency can be improved, the generated mid-femtosecond mid-infrared laser pulse has the advantages of wide tuning range and high repetition frequency, and the output mid-infrared femtosecond optical power can be improved by increasing the power of the initial pumping light. The Optical Parametric Oscillation (OPO) can realize continuous tunable wavelength output within a wider frequency spectrum range, and meanwhile, the ultra-short middle infrared pulse is obtained by adopting a difference frequency method (DFG), so that the Optical Parametric Oscillation (OPO) has the advantages of good beam quality, no need of a resonant cavity and the like, and finally, the high-power wide-tuning middle infrared laser output can be obtained, the stability of the output laser is good, and the OPO can be widely applied to the fields of air pollution detection, remote sensing, spectral analysis, military and the like.
Through the above analysis, the problems and defects existing in the prior art are as follows: the prior art for generating the mid-infrared femtosecond laser has low output power, narrow tuning range and high requirement on nonlinear crystals.
The difficulty of solving the problems and the defects is as follows: on the one hand, the requirement on nonlinear crystal is high, if a1 μm high-power ytterbium-doped femtosecond laser is adopted for pumping, if the conventional crystal is high in transmission to 1 μm, the wavelength of long wave generated by multiphoton absorption is limited to 4-5 μm, and high-power laser with longer wavelength cannot be directly generated, but ZGP crystal with extremely excellent optical property capable of generating infrared output in long wavelength cannot transmit light in the wave band below 2 μm and cannot be directly pumped by the 1 μm laser. Therefore, the 1 μm pump source laser is required to be converted into two laser beams with longer wavelengths, and ZGP crystals with excellent optical properties are utilized to generate high-power mid-infrared tunable femtosecond laser in a difference frequency mode. On the other hand, if the OPO or DFG technology is used alone to output mid-infrared femtosecond laser, the output power or tuning range thereof is limited, and it is difficult to directly obtain high-power continuous wide-tuning laser output near mid-far infrared wavelength, so that it is considered to increase the conversion efficiency by taking difference frequency through a plurality of nonlinear processes, and the generated mid-infrared femtosecond laser pulse has the advantages of wide tuning range and high repetition frequency, and the output mid-infrared femtosecond optical power can be increased by increasing the power of the initial pump light.
The meaning of solving the problems and the defects is as follows: firstly, converting 1 mu m pump source laser into two beams of femtosecond laser with longer wavelength by utilizing an OPO technology, and meanwhile, tuning the wavelength range of the two beams of femtosecond laser, and then generating high-power middle-infrared tunable femtosecond laser in a difference frequency mode by utilizing ZGP crystals with excellent optical properties. The scheme solves the problems of low output power and narrow tuning range of the existing femtosecond laser output technology, breaks through the design scheme of the traditional laser generating device, has clear system principle and relatively low requirements on a pumping source and a nonlinear crystal, generates the mid-infrared femtosecond laser, has high output power and adjustable wavelength range, has good stability of the output laser, can be widely applied to the aspects of free space optical communication, trace gas detection, environmental monitoring, biomedicine and the like, and has great application value.
Disclosure of Invention
Aiming at the problems existing in the prior art, the invention provides a high-power middle-infrared tunable femtosecond laser generating device, a control method and application.
The invention is realized in that a high-power mid-infrared tunable femtosecond laser generating device comprises:
the pumping module is used for pumping the optical parametric oscillation module;
the optical parametric oscillation module is used for converting input laser or pump light into two output lights with lower frequencies;
and the difference frequency generation module is used for carrying out difference frequency on the two laser beams generated by the optical parametric oscillation module to generate high-power middle-infrared tunable femtosecond laser.
Further, the pump module includes: the high-power femtosecond oscillator, the first half-wave plate, the polarizing prism and the second half-wave plate;
The center wavelength of the high-power femtosecond oscillator is 1030nm, the pulse width is 100fs, and the average power is more than 8W, so that the high-power femtosecond oscillator is used for pumping optical parametric oscillation modules; the first half wave plate and the polarizing prism form a power attenuator for changing the power of the pump light; the second half-wave plate is used for adjusting the polarization direction of the pump light, so that the power and polarization of the pump light can be tuned.
Further, the optical parametric oscillation module includes: the lens comprises a first focusing lens, a first concave mirror, a nonlinear crystal and a second concave mirror;
The first focusing lens is used for focusing the laser output by the pumping source onto the nonlinear crystal, so that the size of an incident light spot of the laser is matched with the size of an oscillation light spot in the cavity; the nonlinear crystal is used for generating tunable signal light and pump light required by a subsequent difference frequency generation module; the first concave mirror is used for transmitting the pump light in a high-transmittance mode and reflecting the signal light in a high-reflectance mode, the second concave mirror is used for transmitting the pump light and the idler light in a high-transmittance mode and reflecting the signal light in a high-reflectance mode, and the nonlinear crystal is arranged between the first concave mirror and the second concave mirror.
Further, the nonlinear crystal is a KTA crystal, characterized in that the crystal cut angle is θ=41.3°,The length is 2mm, and the size range of the light spot of the pump light which is focused and incident on the crystal is 40-70 mu m; the KTA crystal is coated with an antireflection film on the two sides of the pump light and the signal light, the output of the signal light with the wavelength of 1.5-1.9 mu m is obtained through angle tuning, the output power is more than 2W, the corresponding output idler frequency optical wavelength range is 2.3-3.2 mu m, and the output power is more than 1W.
Further, the optical parametric oscillation module further comprises a first high-reflection mirror, a second high-reflection mirror, a third high-reflection mirror and an output mirror;
The first high-reflection mirror, the second high-reflection mirror and the third high-reflection mirror are used for carrying out high-reflection on the signal light, and keep the signal light oscillating in the cavity; the output mirror is used for transmitting signal light and placing the signal light on the one-dimensional translation stage for adjusting the optical parameter oscillation cavity length so as to realize cavity length matching.
Further, the difference frequency generation module includes: a third focusing lens, a nonlinear crystal, a fourth focusing lens;
The third focusing lens is used for focusing the pump light and the signal light which are collinear with the laser to the nonlinear crystal, so that the size of an incident light spot of the third focusing lens is matched with the size of a light spot in the cavity; the nonlinear crystal is used for taking the signal light and the idler frequency light generated by the optical parametric oscillation module as pump light and signal light respectively to carry out difference frequency so as to obtain high-power middle-infrared tunable femtosecond laser; the fourth focusing lens is used for collimating and outputting the generated high-power mid-infrared femtosecond laser, and the nonlinear crystal is arranged between the third focusing lens and the fourth focusing lens;
the nonlinear crystal is ZGP crystal, which is characterized in that the cutting angle of the crystal is theta=74.3 degrees, When the crystal is used for outputting 4-7 mu m difference frequency light, the crystal cutting angle is theta=55.8 DEG,When the crystal is used for outputting 7-9 mu m difference frequency light, the required crystal length is 1mm; and obtaining the middle infrared femtosecond laser with adjustable wavelength range of 4-9 mu m through angle phase matching tuning, wherein the output power of the middle infrared femtosecond laser is more than 100mW in the whole idler frequency light range.
Further, a second focusing lens and a time delay device are arranged between the idler frequency light output end of the optical parametric oscillation module and the third focusing lens of the difference frequency generation module, and the second focusing lens and the time delay device are used for focusing and collimating the generated idler frequency light and enabling the generated idler frequency light to coincide and match with the signal light in space and time.
Further, a first beam splitter is arranged in front of the difference frequency generation module and used for reflecting idler frequency light output by the OPO module, transmitting signal light and enabling two beams of light to be incident on a third focusing lens at the same time for focusing; the second beam splitter is arranged behind the difference frequency generation module and is used for transmitting the high-power tunable middle infrared laser generated by the difference frequency and reflecting the rest light.
Another object of the present invention is to provide a control method of the high-power mid-infrared tunable femtosecond laser generation apparatus, the control method comprising:
the high-power femtosecond oscillator is used as a pumping source for pumping the OPO optical parametric oscillation module and outputting pumping light; the first half-wave plate and the polarizing prism form a power attenuator, the power of the pump light can be changed by rotating the first half-wave plate, and the second half-wave plate is used for adjusting the polarization direction of the pump light, so that the tunable power and polarization of the pump light can be realized finally;
the pump light is transmitted through the high-reflection mirrors a1 and a2 and focused on the nonlinear crystal KTA through the first focusing lens, and an optical parametric oscillation process is carried out in the OPO cavity to generate signal light and idler frequency light; the first concave mirror is high in transmission of the pump light and high in reflection of the signal light, the second concave mirror is high in transmission of the pump light and the idler light and high in reflection of the signal light, and the nonlinear crystal is arranged between the first concave mirror and the second concave mirror;
the first high-reflection mirror, the second high-reflection mirror and the third high-reflection mirror also carry out high reflection on the signal light, and continuously tunable signal light and idler frequency light output are realized by changing the phase matching angle of the KTA crystal; the signal light is output through the output mirror, reflected twice by the high reflection mirrors c1 and c2 and overlapped with the idler frequency light;
Setting a second focusing lens at the idle frequency light output position to enable the idle frequency light spot size to be matched with the signal light spot size, and enabling light to be delayed and combined with the signal light simultaneously by setting high-reflection mirrors b1, b2 and b 3;
The first beam splitter is used for transmitting signal light, reflecting idler frequency light, and focusing the idler frequency light on a nonlinear crystal ZGP through a third focusing lens to perform a difference frequency generation process; the tunable signal light and the idler frequency light output by the OPO optical parametric oscillation module are used as pump light and signal light of a subsequent difference frequency generation module to generate a difference frequency effect, high-power tunable mid-infrared femtosecond laser is output, and the high-power tunable mid-infrared femtosecond laser is focused and collimated by a fourth focusing lens to be output; the second beam splitter is used for transmitting the high-power tunable middle infrared laser and reflecting the rest light.
It is another object of the present invention to provide an application of the high-power mid-infrared tunable femtosecond laser generating device in free space optical communication, trace gas detection, environmental monitoring or biomedical.
By combining all the technical schemes, the invention has the advantages and positive effects that: the invention adopts a high-power 1 mu m laser for pumping, utilizes the technology of combining Optical Parametric Oscillation (OPO) and Difference Frequency Generation (DFG), adopts ZGP crystals for difference frequency generation, and finally outputs the mid-infrared femtosecond laser, thereby not only having the advantage of high power, but also having great application value. The high-power tunable mid-infrared femtosecond laser is obtained, and the high-power, high-repetition frequency and wide tuning of the output laser are ensured to a certain extent by utilizing the research scheme of OPO+DFG.
The high-power femtosecond oscillator pump OPO optical parametric oscillation module generates tunable signal light and idler frequency light which are respectively used as pump light and signal light differential frequency required by the DFG differential frequency generation module to generate middle-infrared femtosecond laser, and the output laser has the characteristic of high-power tunability.
The invention adopts the OPO+DFG combination scheme to obtain the high-power mid-infrared tunable femtosecond laser, solves the problems of low output power and narrow tuning range of the existing femtosecond laser output technology, breaks through the design scheme of the traditional laser generating device, and utilizes the combination technology to obtain the mid-infrared femtosecond laser.
The femtosecond laser generated by the invention has high output power and adjustable wavelength range, and meanwhile, the system has clear principle, flexible and simple structure and relatively low requirements on a pumping source and a nonlinear crystal.
Drawings
FIG. 1 is a schematic diagram of a high-power mid-infrared tunable femtosecond laser generating device provided by an embodiment of the invention;
In fig. 1: 1. a high power femtosecond oscillator; 2. a first half-wave plate; 3. a polarizing prism; 4. a second half-wave plate; 5. a first focusing lens; 6. a first concave mirror; 7. a nonlinear crystal KTA; 8. a second concave mirror; 9. a first high reflection mirror; 10. a second high reflection mirror; 11. a third high reflection mirror; 12. an output mirror; 13. a second focusing lens; 14. a first beam splitter; 15. a third focusing lens; 16. a nonlinear crystal ZGP; 17. a fourth focusing lens; 18. and a second beam splitter. a1, a2:45 degree planar high reflection mirror (1030 nm); b1, b2, b3:45 degree plane high reflection mirror (2300-3200 nm); c1, c2:45 degree plane high reflection mirror (1500-1900 nm).
FIG. 2 shows that under the condition of KTA crystal class II phase matching, pump light is 1030nm, the tunable range of output signal light is 1.5-1.9 μm, the tunable range of corresponding idler frequency light wavelength is 2.3-3.2 μm, and the corresponding phase matching angle is 41.3-46.4 degrees.
FIG. 3 shows that under the condition of ZGP crystal class I phase matching, tunable signal light and idler light generated by an optical parametric oscillation module are respectively used as pump light and signal light to generate idler light in a difference frequency process, and meanwhile, the range of the corresponding pump light is selected to be 1.65-1.85 mu m, the range of the signal light is selected to be 2.32-2.74 mu m in consideration of larger transmittance, so that the range of the output idler light is 4-9 mu m, and the corresponding phase matching angle is 53.7-86.2 degrees.
Detailed Description
The present invention will be described in further detail with reference to the following examples in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
Aiming at the problems existing in the prior art, the invention provides a high-power middle-infrared tunable femtosecond laser generating device, a control method and application, and the invention is described in detail below with reference to the accompanying drawings.
The invention provides a scheme which has clear system principle, simpler structure and relatively lower requirement on a pumping source and a nonlinear crystal to acquire mid-infrared femtosecond laser, namely a high-power mid-infrared tunable femtosecond laser generating device designed by utilizing the combination technology of OPO+DFG.
As shown in fig. 1, the invention is a high-power mid-infrared tunable femtosecond laser generating device designed by utilizing the combination technology of opo+dfg, which comprises three modules: the system comprises a pumping module, an Optical Parametric Oscillation (OPO) module and a Difference Frequency Generation (DFG) module.
The pumping module is used for pumping the OPO optical parametric oscillation module;
Specifically, the pump module includes: a high power femtosecond oscillator 1, a first half wave plate 2, a polarizing prism 3 and a second half wave plate 4. The high-power femtosecond oscillator 1 is used for pumping an OPO optical parametric oscillation module; the first half wave plate 2 and the polarizing prism 3 form a power attenuator for changing the power of the pump light; the second half-wave plate 4 is used for adjusting the polarization direction of the pump light, and finally realizing the tunable pump light power and polarization.
The Optical Parametric Oscillation (OPO) module is used for converting input laser (pump light) into two output lights (signal light and idler light) with lower frequencies;
specifically, the optical parametric oscillation module is used for generating tunable signal light (1.5-1.9 μm) and idler light (2.3-3.2 μm) to prepare for the subsequent difference frequency generation module. The first focusing lens 5 is used for focusing the pump light onto the nonlinear crystal KTA, ensuring that the light spot size is consistent with the size of the oscillation light spot in the cavity, and ensuring that the light transmission time is consistent with the oscillation light in the cavity and synchronous pumping is maintained. Further, parameters and distances of all elements in the resonant cavity are determined by simulating the OPO cavity type, so that the signal light oscillates in the cavity, the optical parametric oscillation process is ensured, and the generated signal light and idler frequency light are output at two ends.
The Difference Frequency Generation (DFG) module is used for performing difference frequency on the two laser beams generated by the OPO module to generate high-power middle-infrared tunable femtosecond laser;
Specifically, the difference frequency generation module is used for generating high-power tunable middle infrared femtosecond laser (4-9 μm) by taking tunable signal light and idler frequency light output by the parametric oscillation module as pump light and signal light required by the difference frequency. The third focusing lens 15 is used for focusing the pump light and the signal light which are collinear with the laser onto the nonlinear crystal ZGP16, and makes the laser focusing light spot as small as possible under the condition that the peak power density of the laser is smaller than the crystal damage threshold value so as to obtain the output of the high-power difference frequency light. Meanwhile, the nonlinear crystal ZGP16 is used for generating a difference frequency effect to obtain mid-infrared laser, and the fourth focusing lens 17 is used for collimating and outputting the generated high-power mid-infrared femtosecond laser.
Specifically, a second focusing lens 13 and a time delay device are arranged between the idler light output end of the Optical Parametric Oscillation (OPO) module and the third focusing lens 15 of the difference frequency generation module, and are used for focusing and collimating the generated idler light and enabling the generated idler light to be overlapped and matched with the signal light in space and time.
Specifically, a first beam splitter 14 is disposed before a Difference Frequency Generation (DFG) module, and is configured to reflect idler light output by an OPO module, transmit signal light, and make two beams of light incident on a third focusing lens 15 at the same time for focusing; a second beam splitter 18 is arranged after the difference frequency generation module for transmitting the high-power tunable mid-infrared laser generated by the difference frequency and reflecting the rest of the light.
The invention firstly operates a high-power femtosecond oscillator 1 which is used as a pumping source for pumping an OPO optical parametric oscillation module, and outputs pump light with the central wavelength of 1030nm and the average power of more than 8W. The first half wave plate 2 and the polarizing prism 3 form a power attenuator, the power of the pump light can be changed by rotating the first half wave plate, and the second half wave plate 4 is used for adjusting the polarization direction of the pump light, so that the tunable pump light power and polarization can be finally realized. The pump light is transmitted through the high-reflection mirrors a1 and a2, focused on a nonlinear crystal (KTA) 7 through a first focusing lens 5, and subjected to an optical parametric oscillation process in an OPO cavity to generate signal light and idler frequency light. The first concave mirror 6 is highly transparent to the pump light and highly reflective to the signal light, the second concave mirror 8 is highly transparent to the pump light and the idler light and highly reflective to the signal light, and the nonlinear crystal 7 is disposed between the first concave mirror and the second concave mirror. The first high reflection mirror 9, the second high reflection mirror 10, and the third high reflection mirror 11 also high reflect the signal light, keeping it oscillating in the cavity. By changing the phase matching angle of the KTA crystal, continuously tunable signal light and idler light output can be realized. The signal light is output by the output mirror 12, reflected twice by the high reflection mirrors c1 and c2, and then overlaps with the idler light. The second focusing lens 13 is arranged at the idler light output position to enable the size of the idler light spot to be matched with that of the signal light spot, and the high-reflection mirrors b1, b2 and b3 are arranged to enable light to be delayed and combined with the signal light simultaneously. The beam splitter 14 is used to transmit signal light, reflect idler light, and focus on a nonlinear crystal (ZGP) 16 via a third focusing lens 15 for a difference frequency generation process. Namely, tunable signal light and idler frequency light output by the OPO optical parametric oscillation module are used as pump light and signal light of a subsequent difference frequency generation module to generate a difference frequency effect, high-power tunable mid-infrared femtosecond laser is output, and the high-power tunable mid-infrared femtosecond laser is focused and collimated and output through a fourth focusing lens 17. The beam splitter 18 is used to pass the high power tunable mid-infrared laser light and reflect the rest of the light.
In the description of the present invention, unless otherwise indicated, the meaning of "a plurality" is two or more; the terms "upper," "lower," "left," "right," "inner," "outer," "front," "rear," "head," "tail," and the like are used as an orientation or positional relationship based on that shown in the drawings, merely to facilitate description of the invention and to simplify the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore should not be construed as limiting the invention. Furthermore, the terms "first," "second," "third," and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.
The foregoing is merely illustrative of specific embodiments of the present invention, and the scope of the invention is not limited thereto, but any modifications, equivalents, improvements and alternatives falling within the spirit and principles of the present invention will be apparent to those skilled in the art within the scope of the present invention.
Claims (6)
1. A high-power middle-infrared tunable femtosecond laser generating device is characterized in that, the high-power mid-infrared tunable femtosecond laser generation device comprises:
the pumping module is used for pumping the optical parametric oscillation module;
the optical parametric oscillation module is used for converting input laser or pump light into two output lights with lower frequencies;
The difference frequency generation module is used for carrying out difference frequency on the two laser beams generated by the optical parametric oscillation module to generate high-power middle-infrared tunable femtosecond laser;
the pump module includes: the high-power femtosecond oscillator, the first half-wave plate, the polarizing prism and the second half-wave plate;
The center wavelength of the high-power femtosecond oscillator is 1030nm, the pulse width is 100fs, and the average power is more than 8W, so that the high-power femtosecond oscillator is used for pumping optical parametric oscillation modules; the first half wave plate and the polarizing prism form a power attenuator for changing the power of the pump light; the second half-wave plate is used for adjusting the polarization direction of the pump light to realize the tunable pump light power and polarization;
The optical parametric oscillation module includes: the lens comprises a first focusing lens, a first concave mirror, a nonlinear crystal and a second concave mirror;
the first focusing lens is used for focusing the laser output by the pumping source onto the nonlinear crystal, so that the size of an incident light spot of the laser is matched with the size of an oscillation light spot in the cavity; the nonlinear crystal is used for generating tunable signal light and pump light required by a subsequent difference frequency generation module; the first concave mirror is used for transmitting the pump light in a high-transmittance mode and reflecting the signal light in a high-reflectance mode, the second concave mirror is used for transmitting the pump light and the idler light in a high-transmittance mode and reflecting the signal light in a high-reflectance mode, and the nonlinear crystal is arranged between the first concave mirror and the second concave mirror;
The optical parametric oscillation module further comprises a first high-reflection mirror, a second high-reflection mirror, a third high-reflection mirror and an output mirror;
The first high-reflection mirror, the second high-reflection mirror and the third high-reflection mirror are used for carrying out high-reflection on the signal light, and keep the signal light oscillating in the cavity; the output mirror is used for transmitting signal light and placing the signal light on the one-dimensional translation stage for adjusting the optical parameter oscillation cavity length so as to realize cavity length matching;
the difference frequency generation module comprises: a third focusing lens, a nonlinear crystal, a fourth focusing lens;
The third focusing lens is used for focusing the pump light and the signal light which are collinear with the laser to the nonlinear crystal, so that the size of an incident light spot of the third focusing lens is matched with the size of a light spot in the cavity; the nonlinear crystal is used for taking the signal light and the idler frequency light generated by the optical parametric oscillation module as pump light and signal light respectively to carry out difference frequency so as to obtain high-power middle-infrared tunable femtosecond laser; the fourth focusing lens is used for collimating and outputting the generated high-power mid-infrared femtosecond laser, and the nonlinear crystal is arranged between the third focusing lens and the fourth focusing lens;
the nonlinear crystal is ZGP crystal, which is characterized in that the cutting angle of the crystal is theta=74.3 degrees, When the crystal is used for outputting 4-7 mu m difference frequency light, the crystal cutting angle is theta=55.8 DEG,When the crystal is used for outputting 7-9 mu m difference frequency light, the required crystal length is 1mm; and obtaining the middle infrared femtosecond laser with adjustable wavelength range of 4-9 mu m through angle phase matching tuning, wherein the output power of the middle infrared femtosecond laser is more than 100mW in the whole idler frequency light range.
2. The high-power mid-infrared tunable femtosecond laser generation apparatus as recited in claim 1, wherein the nonlinear crystal is KTA crystal, wherein a crystal cut angle is θ=41.3 °,The length is 2mm, and the size range of the light spot of the pump light which is focused and incident on the crystal is 40-70 mu m; the KTA crystal is coated with an antireflection film on the two sides of the pump light and the signal light, the output of the signal light with the wavelength of 1.5-1.9 mu m is obtained through angle tuning, the output power is more than 2W, the corresponding output idler frequency optical wavelength range is 2.3-3.2 mu m, and the output power is more than 1W.
3. The high-power mid-infrared tunable femtosecond laser generation apparatus of claim 1, wherein a second focusing lens and a time delay device are disposed between an idler light output end of the optical parametric oscillation module and a third focusing lens of the difference frequency generation module, for focusing and collimating the generated idler light and overlapping and matching with the signal light in space and time.
4. The high-power mid-infrared tunable femtosecond laser generation device of claim 1, wherein a first beam splitter is arranged in front of the difference frequency generation module and used for reflecting idler light output by the OPO module, transmitting signal light and enabling two beams of light to be incident on a third focusing lens at the same time for focusing; the second beam splitter is arranged behind the difference frequency generation module and is used for transmitting the high-power tunable middle infrared laser generated by the difference frequency and reflecting the rest light.
5. A control method of the high-power mid-infrared tunable femtosecond laser generation apparatus as set forth in any one of claims 1 to 4, wherein the control method includes:
the high-power femtosecond oscillator is used as a pumping source for pumping the OPO optical parametric oscillation module and outputting pumping light; the first half-wave plate and the polarizing prism form a power attenuator, the power of the pump light can be changed by rotating the first half-wave plate, and the second half-wave plate is used for adjusting the polarization direction of the pump light, so that the tunable power and polarization of the pump light can be realized finally;
the pump light is transmitted through the high-reflection mirrors a1 and a2 and focused on the nonlinear crystal KTA through the first focusing lens, and an optical parametric oscillation process is carried out in the OPO cavity to generate signal light and idler frequency light; the first concave mirror is high in transmission of the pump light and high in reflection of the signal light, the second concave mirror is high in transmission of the pump light and the idler light and high in reflection of the signal light, and the nonlinear crystal is arranged between the first concave mirror and the second concave mirror;
the first high-reflection mirror, the second high-reflection mirror and the third high-reflection mirror also carry out high reflection on the signal light, and continuously tunable signal light and idler frequency light output are realized by changing the phase matching angle of the KTA crystal; the signal light is output through the output mirror, reflected twice by the high reflection mirrors c1 and c2 and overlapped with the idler frequency light;
Setting a second focusing lens at the idle frequency light output position to enable the idle frequency light spot size to be matched with the signal light spot size, and enabling light to be delayed and combined with the signal light simultaneously by setting high-reflection mirrors b1, b2 and b 3;
The first beam splitter is used for transmitting signal light, reflecting idler frequency light, and focusing the idler frequency light on a nonlinear crystal ZGP through a third focusing lens to perform a difference frequency generation process; the tunable signal light and the idler frequency light output by the OPO optical parametric oscillation module are used as pump light and signal light of a subsequent difference frequency generation module to generate a difference frequency effect, high-power tunable mid-infrared femtosecond laser is output, and the high-power tunable mid-infrared femtosecond laser is focused and collimated by a fourth focusing lens to be output; the second beam splitter is used for transmitting the high-power tunable middle infrared laser and reflecting the rest light.
6. Use of a high power mid-infrared tunable femtosecond laser generation apparatus as defined in any one of claims 1 to 4 in free space optical communication, trace gas detection, environmental monitoring or biomedical.
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