CN107221830A - A kind of unsteady cavity single-frequency laser output device - Google Patents

Abstract

The application provides an unstable cavity single-frequency laser output device, including: a seed laser oblique injection system and a laser resonance system; the seed laser oblique injection system includes: a waveguide laser, a first beam splitter, a beam quality analyzer, a second A reflective mirror, a second reflective mirror and a beam expander; the laser resonance system includes: a first electrode and a second electrode arranged oppositely, located on both sides of the first electrode and the second electrode, and a concave reflector and a concave-convex part arranged oppositely The reflector, the reflector of the output beam of the laser resonance system is a concave-convex partial reflector, and the positive branch virtual confocal unstable cavity is a transmission output mode, which can emit a solid spot and realize the output of a near-field solid spot; and the incident to the first electrode The beam is injected obliquely at the end face, and the electrode reflected beam is used for injection locking, which can obtain a single-frequency laser output, and to a certain extent reduces the complexity of seed injection optical path design adjustment and optical isolation, which is conducive to improving system stability.

Description

An Unstable Cavity Single Frequency Laser Output Device

technical field

The invention relates to the technical field of high-power lasers, in particular to an unstable cavity single-frequency laser output device.

Background technique

With the increasing demand for detection and recognition of long-distance targets, the detection methods for such targets are gradually enriched. Among them, laser coherent detection, as a non-contact interferometric technology, has the advantages of high sensitivity and strong anti-interference ability. Its importance is gradually highlighted in the above applications. To achieve coherent measurement and recognition of long-distance targets, laser emission sources with high spectral purity and stable frequency are required, and such emission sources are mainly obtained by seed injection locking technology.

At present, there are many ways to realize high-power single-frequency laser output. Among them, the injection-locking method based on stable cavity has the characteristics of simple structure and good stability. Under the same gain medium volume, the energy obtained by single-frequency operation is low, which limits its further use. The injection locking technology based on the unsteady cavity output can make full use of its excellent transverse mode discrimination ability (reasonably designed cavity type has quasi-fundamental mode operation ability), combined with the seed injection locking technology, under the same gain volume, it can Obtain higher energy single transverse mode output. On this basis, the longitudinal mode of oscillation is selected by seed injection to realize single-frequency operation. This method is currently the mainstream method for realizing high-power single-frequency laser output in typical international application systems.

However, the traditional positive-branched virtual confocal unstable cavity design mainly adopts a reflective output structure, and the output spot is a hollow beam in the near field. Although it is diffracted into a central solid beam after about 20m, but in the near-field optical transmission and relay system In design, it is still relatively inconvenient.

Contents of the invention

In view of this, the present invention provides an unstable cavity single-frequency laser output device to solve the problem in the prior art that the positive branch virtual confocal unstable cavity with a reflective output structure outputs a solid beam in near-field optics. .

To achieve the above object, the present invention provides the following technical solutions:

An unstable cavity single-frequency laser output device, comprising:

Seed laser oblique injection system and laser resonance system;

The seed laser oblique injection system includes: a waveguide laser, a first beam splitter, a beam quality analyzer, a first mirror, a second mirror and a beam expander;

The laser resonance system includes: a first electrode and a second electrode arranged oppositely, a concave reflector and a concave-convex part reflector arranged oppositely on both sides of the first electrode and the second electrode;

The central axis of the first electrode and the second electrode is on the same straight line as the optical axis of the concave reflector and the concave-convex partial reflector;

Wherein, the beam emitted by the waveguide laser is divided into a transmitted first beam and a reflected second beam through the first beam splitter, and the second beam is incident on the beam quality analyzer, and the beam quality analyzer is used to monitor a laser mode of the second light beam;

The first light beam is expanded by the beam expander, passes through a periscope structure composed of the first reflector and the second reflector, and obliquely enters the first electrode;

After the light obliquely incident on the first electrode is scattered by the first electrode, it is reflected multiple times by the concave reflector and the concave-convex partial reflector, and exits through the concave-convex partial reflector to obtain a single-frequency Laser, the single-frequency laser is a solid spot.

Preferably, the unstable cavity single-frequency laser output device further includes a single-frequency laser output detection system, a second beam splitter and a third beam splitter;

The second beam splitter is used to divide the second light beam into a reflected third light beam and a transmitted fourth light beam, the fourth light beam is incident on the beam quality analyzer, and the third light beam is used as the The reference beam of the single-frequency laser output detection system;

The third beam splitter is used to divide the single-frequency laser emitted by the concave-convex partial reflector into a transmitted fifth beam and a reflected sixth beam, and the fifth beam is used as the unstable cavity single-frequency laser output device The effective energy output of the sixth light beam is input to the single-frequency laser detection system for laser pulse frequency detection;

Wherein, the single-frequency laser output detection system is used to detect the frequency of the single-frequency laser.

Preferably, the single-frequency laser output detection system includes: a polarizer, a fourth beam splitter, a controllable attenuator group, a photodetector and an oscilloscope;

The sixth light beam is transmitted to the photodetector through the fourth beam splitter after passing through the polarizer;

The third light beam is reflected to the photodetector by the fourth beam splitter after passing through the controllable attenuator group;

The output end of the photodetector is connected to the input end of the oscilloscope, and the oscilloscope is used to output a pulse waveform.

Preferably, the transmittance ratio of the first beam splitter is 4:1.

Preferably, the beam expander is a 5-fold beam expander.

Preferably, the reflectivity of the concave mirror is higher than 99%.

Preferably, the reflectivity of the concave-convex partial reflector is 70%.

Preferably, the transmittance ratio of the third beam splitter is 9:1.

Preferably, the waveguide laser is a waveguide _CO2 laser.

It can be seen from the above technical solution that in the unstable cavity single-frequency laser output device provided by the present invention, the reflector of the output beam of the laser resonance system is a concave-convex partial reflector, that is, the positive branch virtual confocal unstable cavity in the present invention is Transmission output mode, so that it can emit a solid spot and realize near-field solid spot output; on the other hand, the beam incident to the first electrode is injected obliquely from the end face, and the reflected beam of the electrode is used for injection locking, so that single-frequency laser output can be obtained. And to a certain extent, it reduces the complexity of seed injection optical path design adjustment and optical isolation, which is beneficial to improve system stability.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only It is an embodiment of the present invention, and those skilled in the art can also obtain other drawings according to the provided drawings without creative work.

Fig. 1 is the structural representation of the reflective positive branch virtual confocal unstable cavity provided by the prior art;

Fig. 2 is a structural schematic diagram of an unstable cavity single-frequency laser output device provided by an embodiment of the present invention;

Fig. 3 is a schematic structural diagram of another unstable cavity single-frequency laser output device provided by an embodiment of the present invention.

detailed description

As mentioned in the background technology section, the traditional positive branch virtual confocal unstable cavity design in the prior art mainly adopts a reflective output structure, as shown in Figure 1, which is the traditional positive branch virtual confocal unstable cavity in the prior art , the positive branch virtual confocal unstable cavity includes a first electrode 01, a second electrode 02, and a first mirror 03 and a second mirror 04 located at both ends of the first electrode 01 and the second electrode 02, wherein the second reflection The size of the mirror 04 is smaller than the size of the first mirror 03, so that when the final beam is output, it can emerge from the edge of the second mirror 04, and therefore, the light spot output by the traditional positive branch virtual confocal unstable cavity is a hollow spot, As shown in Figure 1. Although the diffraction becomes a central solid beam after about 20m or the solid beam can be obtained through the reconstruction of the central beam, it is still inconvenient in the design of near-field optical transmission and relay systems.

Based on this, the present invention provides an unstable cavity single-frequency laser output device, including:

Seed laser oblique injection system and laser resonance system;

The seed laser oblique injection system includes: a waveguide laser, a first beam splitter, a beam quality analyzer, a first mirror, a second mirror and a beam expander;

The laser resonance system includes: a first electrode and a second electrode arranged oppositely, a concave reflector and a concave-convex part reflector arranged oppositely on both sides of the first electrode and the second electrode;

The central axis of the first electrode and the second electrode is on the same straight line as the optical axis of the concave reflector and the concave-convex partial reflector;

Wherein, the beam emitted by the waveguide laser is divided into a transmitted first beam and a reflected second beam through the first beam splitter, and the second beam is incident on the beam quality analyzer, and the beam quality analyzer is used to monitor a laser mode of the second light beam;

The first light beam is expanded by the beam expander, passes through a periscope structure composed of the first reflector and the second reflector, and obliquely enters the first electrode;

After the light obliquely incident on the first electrode is scattered by the first electrode, the single-frequency laser light becomes a solid spot after passing through the concave reflector and the concave-convex part reflector.

In the unstable cavity single-frequency laser output device provided by the present invention, the reflector of the output beam of the laser resonance system is a concave-convex partial reflector, that is, the positive branch virtual confocal unstable cavity in the present invention is a transmission output mode, so that it can emit Solid light spot, to achieve near-field solid light spot output; on the other hand, the beam incident to the first electrode is injected obliquely from the end face, and the reflected beam of the electrode is used for injection locking, which can obtain single-frequency laser output, and reduces to a certain extent The complexity of seed injection optical path design adjustment and optical isolation is conducive to improving system stability.

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

Specifically, please refer to FIG. 2. FIG. 2 is a schematic structural diagram of an unstable cavity single-frequency laser output device provided by an embodiment of the present invention. The unstable cavity single-frequency laser output device includes: a seed laser oblique injection system 100 And laser resonance system 200; Seed laser oblique injection system includes: waveguide laser 1, first beam splitter 2, beam quality analyzer 5, first reflection mirror 8, second reflection mirror 9 and beam expander 7; Laser resonance The system includes: a first electrode and a second electrode arranged oppositely, a concave reflector 10 and a concave-convex partial reflector 14 arranged oppositely on both sides of the first electrode and the second electrode; the central axis of the first electrode and the second electrode The optical axis of the concave reflector 10 and the concave-convex partial reflector 14 is located on the same straight line; wherein, the beam emitted by the waveguide laser 1 is divided into a transmitted first beam and a reflected second beam through the first beam splitter 2, and the second The beam is incident on the beam quality analyzer 5, and the beam quality analyzer 5 is used to monitor the laser mode of the second beam; The periscope structure is obliquely incident to the first electrode; after the light incident obliquely to the first electrode is scattered by the first electrode, it is reflected multiple times by the concave reflector 10 and the concave-convex partial reflector 14, and exits through the concave-convex partial reflector 14, A single-frequency laser is obtained, and the single-frequency laser is a solid spot.

It should be noted that, in FIG. 2 , in the oblique seed laser injection system 100, except for the second mirror 9, other components are on the same horizontal plane, and this horizontal plane is in line with the first electrode and the second electrode in the laser resonance system 200. The central axes of the two electrodes, that is, the dotted line shown in FIG. 2 are located in the same horizontal plane. The cross-section of the laser resonator system 200 shown in FIG. 2 is a schematic cross-sectional structural diagram perpendicular to the horizontal plane. That is, the seed laser oblique injection system 100 and the laser resonance system 200 shown in FIG. 2 are located in two mutually perpendicular planes. Wherein, the periscope structure composed of the first reflector 8 and the second reflector 9 realizes the lifting of the optical path, and lifts the light beam located at the horizontal plane of the central axis of the first electrode and the second electrode to be higher than the concave reflector 10, thereby being able to Obliquely incident on the sealing window 11 of the laser resonance system from the edge of the concave mirror 10 , and then obliquely incident on the first electrode 12 relative to the sealing window of the laser resonance system.

In this embodiment, it is not limited whether the first electrode is the upper electrode or the lower electrode, but in the actual optical path arrangement, the seed source and the laser are fixed on the stable substrate, the vertical distance between the discharge area and the substrate is short, and the injection beam is incident on the upper electrode from bottom to top. There is not enough space for light guide when electrodes are used. Therefore, in this embodiment, optionally, the first electrode is the lower electrode. That is, 12 in FIG. 2 is the first electrode, and 13 is the second electrode.

In this embodiment, the end-face oblique injection method is adopted to avoid the beam isolation problem introduced by injection along the central axis of the first electrode and the second electrode.

Since the reflector in the outgoing direction of the laser resonator system in this embodiment is a concave-convex partial reflector 14, the light beam can pass through directly, without needing to exit through the edge of the reflector as in the prior art, so that a solid light beam can be obtained.

In the unstable cavity single-frequency laser output device provided in this embodiment, the reflector of the output beam of the laser resonance system is a concave-convex partial reflector, that is, the positive branch virtual confocal unstable cavity adopts a transmission output mode, so that a solid spot can be emitted, Realize near-field solid spot output; on the other hand, the beam incident to the first electrode is injected obliquely from the end face, and the reflected beam of the electrode is used for injection locking, which can obtain single-frequency laser output and reduce the optical path of seed injection to a certain extent. The complexity of design adjustments and optical isolation is beneficial to improve system stability.

The embodiment of the present invention also provides an unstable cavity single-frequency laser output device, as shown in Figure 3, on the basis of the previous embodiment, it also includes: a single-frequency laser output detection system 300, a second beam splitter 4 and The third beam splitter 15; wherein, the single-frequency laser output detection system 300 is used to detect the frequency of the single-frequency laser. The second beam splitter 4 is used to divide the second beam into a reflected third beam and a transmitted fourth beam, the fourth beam is incident on the beam quality analyzer 5, and the third beam is used as a reference for the single-frequency laser output detection system 300 Light beam; the third beam splitter 15 is used to divide the single-frequency laser emitted by the concave-convex partial reflector 14 into the fifth beam of transmission and the sixth beam of reflection, and the fifth beam is used as the effective energy of the unstable cavity single-frequency laser output device output, the sixth light beam is input to the single-frequency laser detection system 300 for laser pulse frequency detection.

In this embodiment, the single-frequency laser output detection system 300 specifically includes: a polarizer 16, a fourth beam splitter 17, a controllable attenuator group 18, a photodetector 19, and an oscilloscope 20; The four-beam splitter 17 is transmitted to the photodetector 19; the third beam passes through the controllable attenuator group 18 and is reflected to the photodetector 19 through the fourth beam splitter 17; the output end of the photodetector 19 is connected to the input end of the oscilloscope 20 Connected, the oscilloscope 20 is used to output the pulse waveform.

In this embodiment, the seed laser oblique injection system 100 also includes a third reflector 3 and a fourth reflector 6. Of course, when the direction of the optical path needs to be changed, the use of reflectors can also be increased or decreased. In this embodiment, No limit.

Specifically, the specific working principle of the unstable cavity single-frequency laser output device provided in the embodiment of the present invention is as follows:

The unstable cavity single-frequency laser output device is a transmission-type output positive branch virtual confocal unstable cavity single-frequency laser device, as shown in Figure 3, which includes three components, each of which is relatively independent in function to achieve high power Single-frequency laser solid spot output, and also has the function of frequency characteristic detection of the output spot.

Among them, the output power of the waveguide CO ₂ laser 1 is close to 3W, the emitted laser beam is divided into two laser beams with a transmittance ratio of 4:1 by the first beam splitter 2, and the reflected light (second beam) passes through the third reflector 3 and the second laser beam. After the beam splitter 4, the transmitted light (the fourth beam) is monitored by the beam quality analyzer 5 as a seed laser mode, and the reflected light (the third beam) passing through the second beam splitter 4 is used as a reference beam for frequency detection. The transmitted light (first light beam) through the first beam splitter 2 enters the laser resonance system after passing through the fourth reflector 6, the 5x beam expander 7, the first reflector 8 and the second reflector 9, where the beam expands The function of the device 7 is mainly to realize the mode matching between the seed laser and the output single transverse mode laser in the pulsed TEA laser resonant system, and the mode matching effect directly determines the level and stability of the seed injection locking probability.

The seed laser reflected by the second mirror 9 is incident on the surface of the lower electrode 12 of the TEA laser resonance system through the sealed window 11, wherein the lower electrode 12 and the upper electrode 13 form a 19kV-26kV discharge electrode pair, and the surface of the lower electrode 12 is polished metal On the other hand, the incident laser light will be scattered, resulting in the inability to fully utilize the beam deviated from the laser oscillation axis. However, due to the high injection power, as long as a part of the seed laser can suppress the spontaneous emission in the laser resonant system, injection locking can be formed. Whole laser resonance system is made up of concave-convex reflector 10 (reflectivity is higher than 99%) and concave-convex partial reflector 14, wherein, the convex surface of concave-convex partial reflector 14 is 70% reflectivity reflective surface, concave-convex partial reflector 14 is used as output coupling The optical element can obtain a solid spot output, and the beam divergence angle is close to 1mrad. The output beam is divided into two parts after passing through the third beam splitter 15, wherein the transmitted beam (the fifth beam) is output as the effective energy of the laser, and the reflected beam (the sixth beam) ) as the laser pulse frequency detection beam.

After passing through the third beam splitter 15 (transmittance ratio 9:1), the reflected light beam passes through the polarizer 16 and the fourth beam splitter 17, and then enters the surface of the photodetector 19, wherein the seed laser reflected by the second beam splitter 4 After entering the controllable attenuator group 18, it is reflected by the fourth beam splitter 17 and then enters the photodetector 19. The output electrical signal of the photodetector 19 enters the oscilloscope 20 to realize output pulse waveform observation and frequency stability detection.

Among them, the smoothness of the pulse waveform directly reflects the single-frequency characteristics of the laser output. If there are multiple longitudinal mode oscillations, there will be harmonic oscillations with the interval frequency of the longitudinal modes as the baseband signal in the beat frequency waveform, and the frequency conversion function of the oscilloscope The short-term or long-term frequency stability characteristics of the laser can be retrieved in real time.

Remote laser coherent detection has high requirements on the frequency stability of the light source. In the actual application system, it is also necessary to introduce a frequency detection system. The unstable cavity single-frequency laser output device provided by the embodiment of the present invention has a built-in frequency detection system function. The subsequent frequency detection process can be simplified.

It should be noted that the transmittance ratio of each beam splitter and the specific beam expansion factor of the beam expander are not limited in this embodiment. Among them, the transmittance ratio of the first beam splitter 2 needs to ensure that most of the power of the seed laser is transmitted and then injected into the TEA laser resonance system to obtain a better mode suppression effect. The multiple of the beam expander 7 is determined according to the divergence angle of the seed laser and the output beam mode distribution of the TEA laser. If the parameters of the laser resonance system change, the beam expansion multiple will also change to obtain better mode matching. Therefore, the transmittance ratio of the beam splitter and the specific beam expansion factor of the beam expander can be selected according to actual needs.

The unstable cavity single-frequency laser output device provided in this embodiment consists of three parts, which are a seed laser oblique injection system, a laser resonance system, and a single-frequency laser output detection system. The laser resonance system is a TEACO ₂ laser resonance system. The seed laser oblique injection system utilizes the single-frequency laser output from the continuous waveguide CO ₂ , injects it into the lower electrode surface of the laser resonance system after beam mode matching, and uses the electrode reflection signal to realize other non- Suppression of select modes. The TEACO ₂ laser resonance system uses the combination of concave and convex mirrors to realize the transmission output of the unstable cavity and obtain the solid spot distribution. The single-frequency laser output detection system uses seed laser as the local oscillator source to mix with TEA pulses to obtain a stable beat frequency signal, which is used as a frequency characteristic detection method for laser single-frequency operation.

The unstable cavity single-frequency laser output device provided by the embodiment of the present invention can realize single-frequency CO ₂ laser output of Joule level or even greater energy, and can realize laser solid spot output for easy use, and the oblique injection method of the end face effectively avoids injection Optical path isolation problem. In addition, the device can change the output pulse length by changing the gas ratio, and at the same time, the laser medium can be replaced with CO ₂ isotope gas to reduce the attenuation rate of the output laser in atmospheric transmission. The specific achievable indicators are as follows: the output energy is greater than 1J, the pulse repetition frequency is up to 30Hz, the spectral line width of the single-frequency laser is better than 2MHz, and the frequency locking probability of the single-frequency laser is better than 90%.

It should be noted that each embodiment in this specification is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. For the same and similar parts in each embodiment, refer to each other, that is, Can.

The above description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention will not be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (9)

1. An unstable cavity single-frequency laser output device, characterized in that, comprising: Seed laser oblique injection system (100) and laser resonance system (200); The seed laser oblique injection system includes: a waveguide laser (1), a first beam splitter (2), a beam quality analyzer (5), a first reflector (8), a second reflector (9) and an expander Beamer (7); The laser resonance system includes: a first electrode and a second electrode oppositely arranged, located on both sides of the first electrode and the second electrode, and oppositely arranged concave reflective mirrors (10) and concave-convex partial reflective mirrors (14 ); The central axis of the first electrode and the second electrode is on the same straight line as the optical axis of the concave reflector (10) and the concave-convex partial reflector (14); Wherein, the beam emitted by the waveguide laser (1) is divided into a transmitted first beam and a reflected second beam through a first beam splitter (2), and the second beam is incident on the beam quality analyzer (5), The beam quality analyzer (5) is used to monitor the laser mode of the second beam; The first light beam is expanded by the beam expander (7), and passes through the periscope structure composed of the first reflector (8) and the second reflector (9), obliquely incident on the first electrode; After the light obliquely incident on the first electrode is scattered by the first electrode, it undergoes multiple reflections by the concave reflector (10) and the concave-convex part reflector (14), and is reflected by the concave-convex part The mirror (14) is emitted to obtain a single-frequency laser, and the single-frequency laser is a solid spot. 2. The unstable cavity single-frequency laser output device according to claim 1, characterized in that, it also includes a single-frequency laser output detection system (300), a second beam splitter (4) and a third beam splitter (15 ); The second beam splitter (4) is used to divide the second light beam into a reflected third light beam and a transmitted fourth light beam, and the fourth light beam is incident to the beam quality analyzer (5), so The third beam is used as the reference beam of the single-frequency laser output detection system (300); The third beam splitter (15) is used to divide the single-frequency laser emitted by the concave-convex partial reflector (14) into a transmitted fifth beam and a reflected sixth beam, and the fifth beam serves as the non- The effective energy output of the stable cavity single-frequency laser output device, the sixth beam is input to the single-frequency laser detection system (300) for laser pulse frequency detection; Wherein, the single-frequency laser output detection system (300) is used to detect the frequency of the single-frequency laser. 3. The unstable cavity single-frequency laser output device according to claim 2, characterized in that, the single-frequency laser output detection system (300) comprises: a polarizer (16), a fourth beam splitter (17), Controllable attenuator group (18), photodetector (19) and oscilloscope (20); The sixth light beam is transmitted to the photodetector (19) through the fourth beam splitter (17) after passing through the polarizer (16); The third light beam is reflected to the photodetector (19) by the fourth beam splitter (17) after passing through the controllable attenuator group (18); The output terminal of the photodetector (19) is connected with the input terminal of the oscilloscope (20), and the oscilloscope (20) is used for outputting a pulse waveform. 4. The unstable cavity single-frequency laser output device according to claim 1, characterized in that, the transmittance ratio of the first beam splitter (2) is 4:1. 5. The unstable cavity single-frequency laser output device according to claim 1, characterized in that the beam expander (7) is a 5-fold beam expander. 6. The unstable cavity single-frequency laser output device according to claim 1, characterized in that the reflectivity of the concave mirror (10) is higher than 99%. 7. The unstable cavity single-frequency laser output device according to claim 1, characterized in that the reflectivity of the concave-convex partial reflector (14) is 70%. 8. The unstable cavity single-frequency laser output device according to claim 2, characterized in that, the transmittance ratio of the third beam splitter (15) is 9:1. 9. The unstable cavity single-frequency laser output device according to any one of claims 1-8, characterized in that the waveguide laser is a waveguide _CO2 laser.