Miniaturized mid-long wave infrared solid state laser directly pumped by thulium-doped laser to zgp crystal

Abstract

A miniaturized medium-long wave infrared solid laser directly pumped by a thulium-doped laser, the thulium-doped laser takes two center-emission-wavelength 793 nm laser diodes as pump sources, two pieces of Tm:YAP crystals with the same parameters are cascaded and placed in a U-shaped resonant cavity as laser gain medium, an acousto-optic Q crystal controls the cavity loss in the resonant cavity, and pulsed laser with a wavelength of 1.94 mu m is output; after the pulsed thulium laser with a wavelength of 1.94 mu m is taken as pump light and passes through a ZGP-OPO module, signal light with a wavelength of 2.8 mu m and idler light with a wavelength of 6.2 mu m are obtained. The application directly takes the first-order oscillation output 1.94 mu m laser of the Tm laser as a pump source, and outputs medium-long wave infrared laser through ZGP-OPO nonlinearity, so that the overall optical path structure of the medium-long wave laser is simplified, and the electro-optical conversion efficiency is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high-power laser optics, and particularly relates to a miniaturized middle-long wave infrared solid laser directly pumped by a thulium-doped laser and a ZGP crystal. BACKGROUND

[0002] The middle infrared laser waveband is located in the atmospheric window and is widely used in various fields, especially in remote sensing detection, medical application and laser countermeasure. The middle infrared laser plays an indispensable role. The nonlinear frequency conversion technology is a powerful means to obtain middle-long wave infrared pulsed laser because of its high conversion efficiency and wavelength tunable type. Among numerous nonlinear crystals, the zinc germanium phosphide ZnGeP2 (ZGP) has an extremely high nonlinear coefficient, a high damage threshold and good thermal conductivity, so that it can stably operate in the two output states of low repetition rate high energy or high average power high repetition rate. Therefore, at present, the optical parametric oscillation technology route (ZGP-OPO) based on the ZGP crystal is the most mature in the field of middle infrared light sources, and is an important way to realize middle-long infrared waveband pulsed laser.

[0003] The traditional ZGP-OPO technology route uses 2.1 µm pulsed laser emitted by a holmium (Ho) laser as a pump light source, that is, 2.1 µm laser output by a Tm laser pumped Ho laser is used as the pump light source of the ZGP-OPO. However, the Ho-ZGP-OPO system is composed of multiple laser pumps, which leads to low overall electro-optical conversion efficiency; at the same time, the actual optical path is complex and the stability is poor. It is difficult to meet the demand of modern application for miniaturized high-stability laser. In addition, the thermal effect and beam quality degradation problem of the Ho laser further limits the overall performance. SUMMARY

[0004] The purpose of the application is to optimize the problems of low overall electro-optical conversion efficiency, low system stability caused by complex laser optical path structure and poor output beam quality in the traditional ZGP-OPO output middle-long wave laser technology route, and to propose a short wave to middle-long wave infrared all-solid-state laser. The thulium-doped (Tm:YAP) solid-state laser directly pumps the zinc germanium phosphide (ZGP) optical parametric oscillator (OPO), realizes compact structure, high electro-optical conversion efficiency, high beam quality, 2.8 µm middle infrared and 6.2 µm long infrared laser output.

[0005] The technical solution of the application is as follows:

[0006] A miniaturized middle-long wave infrared solid laser directly pumped by a thulium-doped laser and a ZGP crystal, characterized in that it comprises: a 793 nm pump beam collimation and focusing module, a Tm:YAP laser resonant cavity module, a 1.94 µm beam conversion module and a middle-long wave ZGP-OPO module.

[0007] The 793 nm pump beam collimation and focusing module comprises:

[0008] The first and second laser diodes output 793 nm random polarization continuous pump light respectively;

[0009] The two groups of symmetrically arranged 793 nm collimation and focusing plano-convex lens groups are used for collimating and focusing the 793 nm pump light output by the first and second laser diodes respectively and injecting the Tm:YAP crystal;

[0010] The two 45° full reflection mirrors are arranged in the 793 nm collimation and focusing plano-convex lens group and are used for folding the optical path to compress the volume of the laser;

[0011] The Tm:YAP laser resonant cavity module comprises a U-shaped resonant cavity and two Tm:YAP crystals arranged in series in the U-shaped resonant cavity, the long edges of which are coaxially arranged with the optical path, and 1.94 µm laser light is excited by stimulated radiation;

[0012] The 1.94 µm beam transformation module is used for adjusting the spot parameters and the polarization state;

[0013] The middle and long wave ZGP-OPO module comprises an OPO four-letter ring cavity and a ZGP crystal arranged in the OPO four-letter ring cavity, and the ZGP crystal is used to output 2.8 µm and 6.2 µm middle and long wave infrared laser light through nonlinear conversion.

[0014] The Tm:YAP laser resonant cavity module, the two first and second dichroic mirrors are symmetrically arranged perpendicularly on both sides of the two Tm:YAP crystals arranged in series, and the laser resonant cavity is in a "U" shape; the 1.94 μm full reflection plane mirror is used as the front cavity mirror; the 1.94 µm plano-concave output coupling lens is used as the rear cavity output mirror; the acousto-optic Q crystal is arranged between the dichroic mirror and the front cavity mirror; the Fabry-Perot etalon is arranged between the dichroic mirror and the rear cavity mirror.

[0015] The 1.94 µm beam transformation module, the 1.94 µm first plano-concave lens, the 1.94 µm second plano-convex lens and the 1.94 µm third plano-convex lens control the spot diameter and divergence of the 1.94 µm beam to the required size and then inject the ZGP-OPO; the 1.94 µm half-wave plate converts the polarization state of the pump light into horizontal polarization light; then the 45° 1.94 µm polarizing plate reflects and filters out the vertical polarization light, and the transmitted laser is horizontal polarization light.

[0016] The middle-long wave ZGP-OPO module, the first 45° middle wave infrared reflecting mirror, the second 45° middle wave infrared reflecting mirror, the third 45° middle wave infrared reflecting mirror and the 45° middle wave infrared output coupling lens are adjacently and perpendicularly arranged to form an OPO four-letter ring cavity; the ZGP crystal is horizontally arranged between the first 45° middle wave infrared reflecting mirror and the 45° middle wave infrared output coupling lens in a manner that the long side is collinear with the laser propagation direction; and the 45° middle wave infrared beamsplitter reflects and outputs 2.8 short wave infrared laser and 6.2 mu m long wave infrared laser, and transmits and separates 1.94 mu m short wave infrared laser.

[0017] The present application has the following advantages:

[0018] 1. In view of the characteristics that the 1.9 mu m thulium-doped crystal is greatly affected by the thermal lens effect, a double-crystal resonant cavity is used, and in the same laser working substance excitation length, the specific surface area of the double crystal is larger than that of the single crystal, so that the heat dissipation of the crystal is improved, the influence of the thermal effect is reduced, and the output efficiency of the laser is improved;

[0019] 2. The ZGP-OPO middle-long wave laser of the present application directly uses a thulium-doped laser as a pump source, compared with the traditional ZGP-OPO middle-long wave laser pumped by a Ho laser, which innovatively simplifies the structure of the first Ho laser, reduces the system complexity, and improves the overall electro-optical conversion efficiency;

[0020] 3. The ZGP-OPO middle-long wave laser of the present application has a simplified structure, and the main part is composed of only a Tm:YAP laser and a ZGP-OPO structure, which is simple and compact, and the miniaturized system improves the working stability of the laser, is conducive to the conversion of product achievements and promotes technology iteration, and has high commercial value. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 The optical path diagram of the miniaturized middle-long wave solid-state laser directly pumped by a thulium-doped laser and a ZGP crystal. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application will be further described in detail below in combination with the drawings and examples. It should be understood that the technical scheme and parameters described in the specific examples described herein are only a part of the present application, and should not limit the protection scope of the present application.

[0023] The following will be combined Figure 1 The present embodiment is described, and the present embodiment is a miniaturized middle-long wave solid-state laser directly pumped by a thulium-doped laser and a ZGP crystal, as shown in Figure 1As shown in the figure, 1.94 μm pulsed laser output by Tm:YAP laser is used as the pump source of phosphogermanium zinc optical parametric oscillator, and 2.8 μm, 6.2 μm pulsed laser is output based on nonlinear frequency conversion technology.

[0024] The Tm:YAP laser uses a commercial laser diode (LD) as the pump light source of the Tm:YAP laser. The first laser diode 1-1 on the left side generates continuous random polarization continuous laser with a center wavelength of 793 nm. The left pump light is collimated by the 793 nm first plano-convex lens 1-3. The 45° 793 nm first total reflection mirror 1-5 folds the optical path to reduce the overall optical path structure size. Then it is focused by the 793 nm second plano-convex lens 1-7. Similarly, the 793 nm laser output by the second laser diode 1-2 on the right side is also collimated and focused by the collimation and focusing system composed of the 793 nm third plano-convex lens 1-4, the 793 nm fourth plano-convex lens 1-8, and the 45° 793 nm second total reflection mirror 1-6. Both sides of the 793 nm pump light are injected into the "U" type resonant cavity where the Tm:YAP double crystal is located after collimation and focusing by the collimation and focusing lens system, and 1.94 μm laser is excited by stimulated radiation. The Tm:YAP double crystal "U" resonant cavity includes a 1.94 μm total reflection flat mirror 1-13, an acousto-optic Q crystal 1-12, a first dichroic mirror 1-9 and a second dichroic mirror 1-10, a Tm:YAP double crystal 1-11, a Fabry-Perot etalon 1-14, and a 1.94 μm plano-concave output coupling lens 1-15. The two Tm:YAP crystals are placed with their long sides coaxial with the optical path, and the interface distance is 2 mm. The front cavity mirror is a flat mirror, and the rear cavity mirror is a plano-concave mirror, which together form a flat-concave cavity. The acousto-optic Q crystal is placed between the front cavity mirror and the dichroic mirror. The Fabry-Perot etalon is placed between the rear cavity mirror and the dichroic mirror. The 1.94 μm pulsed laser is finally output through the rear cavity mirror for subsequent optical path building.

[0025] 1.94 µm pulse laser through the action of 1.94 µm first plano-concave lens 2-1, 1.94 µm second plano-convex lens 2-5, 1.94 µm third plano-convex lens 2-6 is to control the pump light transmission to the inside of the ZGP crystal for the required spot diameter and divergence; 1.94 µm half-wave plate 2-2 changes the polarization state of 1.94 µm pump light, which is converted to horizontal polarization light, 45° 1.94 µm polarizer 2-4 separates the vertical polarization light from the horizontal polarization light of the input pump light, the horizontal polarization light will continue to transmit along the input light path, and the 45° 1.94 µm total reflection mirror 2-3 folds the light path, making the overall light path structure compact; considering the safety and stability of the internal devices when the laser operates, the half-wave plate, 45° 1.94 µm total reflection mirror and 45° 1.94 µm polarizer are all placed in the large spot area between the first plano-concave lens and the second plano-concave lens; further, the 1.94 µm pump light in horizontal polarization state is injected into the ZGP crystal 2-9 for a type of phase matching, the first 45° mid-wave infrared mirror 2-7, the ZGP crystal 2-9, the second 45° mid-wave infrared mirror 2-8, the third 45° mid-wave infrared mirror 2-10 and the 45° mid-wave infrared output coupling lens 2-11 constitute a germanium-zinc-phosphorus optical parametric oscillator, and the 1.94 µm pump light realizes 2.8 infrared laser output through nonlinear frequency conversion; finally, the output laser passes through the 45° mid-wave infrared spectroscope 2-12 to separate the 1.94 µm short-wave infrared laser, so that the 2.8 short-wave infrared laser is reflected and output together with the 6.2 µm long-wave infrared laser.

[0026] The 793 nm collimating and focusing lens group on both sides of the Tm:YAP resonant cavity is composed of 793 nm first plano-convex lens 1-3 and 793 nm third plano-convex lens 1-4 as collimating lenses, and 793 nm second plano-convex lens 1-7 and 793 nm fourth plano-convex lens 1-8 as focusing lenses, both sides of the lenses are coated with 793 nm anti-reflection film, the focal length is 15 mm-75 mm, and the diameter is 10 mm-15 mm;

[0027] The reflecting surfaces of the 45° 793 nm first total reflection mirror 1-5 and the 45° 793 nm second total reflection mirror 1-6 are coated with 45° 793 nm total reflection film, and the diameter is 15 mm;

[0028] Both sides of the first dichroic mirror 1-9 and the second dichroic mirror 1-10 are coated with 793 nm anti-reflection film, and the reflecting surface is coated with 45° 1.94 µm total reflection film, and the diameter is 15 mm;

[0029] Both light transmitting surfaces of the acousto-optic Q crystal 1-12 are coated with 1.94 µm anti-reflection film;

[0030] 1.94 μm flat-flat mirror 1-13 is a flat-flat mirror, both sides of which are coated with 793 nm anti-reflection film, the reflecting surface is 1.94 μm full reflection film, and the diameter is 15 mm;

[0031] Series Tm:YAP crystal 1-11 is composed of two Tm:YAP crystals with the same parameters, which are placed with the long edges coaxial with the optical path, and the distance between the joint surfaces is 2 mm. Both light transmission surfaces of the single crystal are coated with 793 nm and 1.94 μm anti-reflection films. The crystal size is 4×4×15 mm 3 , the doping concentration is 2at%, and the tangential direction is b-cut;

[0032] The thickness of the Fabry-Perot etalon 1-14 is 0.32 mm;

[0033] 1.94 μm flat-concave output coupling lens 1-15 is coated with 793 nm anti-reflection film on both sides. The reflecting concave surface is coated with a 1.94 μm film layer with a transmittance of 60%~70%, and the transmitting surface is coated with a 1.94 μm anti-reflection film. The concave surface has a curvature radius of 200 mm and a diameter of 20 mm;

[0034] 1.94 μm first flat-concave lens 2-1 is coated with 1.94 μm anti-reflection film on both sides. The concave surface has a curvature radius of -80 mm and a diameter of 15 mm. 1.94 μm second flat-convex lens 2-5 and 1.94 μm third flat-convex lens 2-6 are both coated with 1.94 μm anti-reflection film on both sides. The focal length is 80 mm-200 mm, and the diameter is 15 mm;

[0035] 1.94 μm half-wave plate 2-2 is coated with 1.94 μm anti-reflection film on both sides. The thickness is 0.1 mm, and the diameter is 15 mm;

[0036] 45° 1.94 μm polarizer 2-4 is coated with a 1.94 μm polarizing film on the reflecting surface and a 1.94 μm anti-reflection film on the transmitting surface. The diameter is 15 mm;

[0037] First 45° mid-wave infrared mirror 2-7, second 45° mid-wave infrared mirror 2-8, and third 45° mid-wave infrared mirror 2-10 are both coated with 1.94 μm and 6.2 μm anti-reflection films on both sides. The reflecting surface is coated with a 45° 2.8 μm full reflection film, and the diameter is 15 mm. 45° mid-wave infrared output coupling lens 2-11 is coated with 1.94 μm and 6.2 μm anti-reflection films on both sides. The reflecting surface is coated with a 2.8 μm film layer with a transmittance of 40%~50%;

[0038] ZGP crystal is coated with 1.94 μm, 2.8 μm, and 6.2 μm anti-reflection films on both sides. The size is 6×6×30 mm 3 , the crystal cutting angle = 54.7°;

[0039] 45° mid-wave infrared spectroscope 2-12 is coated with 1.94 μm anti-reflection film on both sides, and the reflecting surface is coated with 2.8 μm and 6.2 μm full reflection films, with a diameter of 20 mm.

[0040] The above only describes the preferred embodiments of the present application, and those skilled in the art should understand that the present application should not be limited by the above, and any modifications, equivalent replacements and improvements made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A miniaturized mid-long wave infrared solid state laser directly pumped by a thulium-doped laser to a ZGP crystal, characterized in that, The application relates to a 1.94 mu m laser device, which comprises the following modules: a 793 nm pump beam collimation and focusing module, a Tm:YAP laser resonant cavity module, a 1.94 mu m beam conversion module and a middle-long wave ZGP-OPO module; the 793 nm pump beam collimation and focusing module comprises: a first laser diode (1-1) and a second laser diode (1-2) for respectively outputting 793 nm random polarization continuous pump light; two groups of symmetrically arranged 793 nm collimation and focusing plano-convex lens groups for respectively collimating and focusing the 793 nm pump light output by the first laser diode (1-1) and the second laser diode (1-2) and injecting the pump light into a Tm:YAP crystal; two 45-degree full reflection mirrors which are arranged in the 793 nm collimation and focusing plano-convex lens groups and are used for folding the optical path to compress the volume of the laser device; the Tm:YAP laser resonant cavity module comprises a U-shaped resonant cavity and two Tm:YAP crystals which are arranged in series in the U-shaped resonant cavity and are arranged in a mode that the long edges are coaxial with the optical path, and the 1.94 mu m laser is excited by stimulated radiation; the 1.94 mu m beam conversion module is used for regulating the spot parameters and the polarization state; the middle-long wave ZGP-OPO module comprises an OPO four-letter ring cavity and a ZGP crystal arranged in the OPO four-letter ring cavity, and the ZGP crystal is used for outputting 2.8 mu m and 6.2 mu m middle-long wave infrared lasers through nonlinear conversion.

2. The miniaturized medium-long wave infrared solid state laser according to claim 1, characterized in that, the U-shaped resonant cavity comprises a first dichroic mirror (1-9), a second dichroic mirror (1-10), an acousto-optic Q crystal (1-12), a 1.94 mu m full reflection flat mirror (1-13), a Fabry-Perot etalon (1-14) and a 1.94 mu m plano-concave output coupling lens (1-15), the first dichroic mirror (1-9) and the second dichroic mirror (1-10) are symmetrically arranged on the two sides of the two Tm:YAP crystals (1-11) arranged in series and are perpendicular to each other, and the first dichroic mirror (1-9) and the second dichroic mirror (1-10) are coated with 793 nm antireflection film and 1.94 mu m full reflection film; the 1.94 mu m full reflection flat mirror (1-13) serves as a front cavity mirror, and the 1.94 mu m plano-concave output coupling lens (1-15) serves as a rear cavity mirror, and the two mirrors together form a U-shaped plano-concave resonant cavity; the acousto-optic Q crystal (1-12) is arranged between the front cavity mirror and the first dichroic mirror (1-9) and is used for controlling the cavity loss and realizing pulse output; the Fabry-Perot etalon (1-14) is arranged between the rear cavity mirror and the second dichroic mirror (1-10) and is used for spectral mode selection.

3. The miniaturized medium-long wave infrared solid state laser according to claim 1 or 2, characterized in that, the two Tm:YAP crystals (1-11) have the same parameters and a spacing of 2-20 mm between the joint surfaces.

4. The miniaturized medium-long wave infrared solid state laser according to claim 1 or 2, characterized in that, the two Tm:YAP crystals (1-11) arranged in series are coated with 793 nm antireflection film and 1.94 mu m antireflection film on both surfaces.

5. The miniaturized mid-long wave infrared solid state laser of claim 2, wherein, the acousto-optic Q crystal (1-12) is coated with 1.94 mu m antireflection film on both light transmission surfaces.

6. The compact mid-long wave infrared solid state laser of claim 1, wherein, The 1.94 µm beam transformation module comprises, in sequence along the optical path, a 1.94 µm first plano-concave lens (2-1), a 1.94 µm half-wave plate (2-2), a 45° 1.94 µm total reflection mirror (2-3), a 45° 1.94 µm polarizer (2-4), a 1.94 µm second plano-convex lens (2-5), and a 1.94 µm third plano-convex lens (2-6); wherein the 1.94 µm first plano-concave lens (2-1), the 1.94 µm second plano-convex lens (2-5), and the 1.94 µm third plano-convex lens (2-6) are used to control the spot diameter and divergence of the 1.94 µm light beam to the required size before injecting into the ZGP-OPO, the 1.94 µm half-wave plate (2-2) is used to convert the 1.94 µm pump light polarization state into horizontal polarization light; the 45° 1.94 µm polarizer (2-4) is used to reflect and filter out the vertical polarized light, and the transmitted laser is horizontal polarized light.

7. The compact mid-long wave infrared solid state laser of claim 6, wherein, The OPO four-letter ring cavity is composed of a first 45° mid-wave infrared reflecting mirror (2-7), a ZGP crystal (2-9), a second 45° mid-wave infrared reflecting mirror (2-8), a third 45° mid-wave infrared reflecting mirror (2-10), and a 45° mid-wave infrared output coupling lens (2-11), and the ZGP crystal (2-9) is horizontally placed between the first 45° mid-wave infrared reflecting mirror (2-7) and the 45° mid-wave infrared output coupling lens (2-11).

8. The miniaturized mid-long wave infrared solid state laser according to claim 2, characterized in that, The thickness of the Fabry-Perot etalon (1-14) is 0.32 mm; both surfaces of the 1.94 µm plano-concave output coupling lens (1-15) are coated with 793 nm anti-reflection film, the concave surface is coated with a 1.94 µm transmission rate of 60%-70% film layer with a curvature radius of 200 mm, and the flat transmission surface is coated with a 1.94 µm anti-reflection film with a diameter of 10 mm.

9. The compact mid-long wave infrared solid state laser of claim 6, wherein The 1.94 µm first plano-concave lens (2-1) is coated with 1.94 µm anti-reflection film on both surfaces, the concave surface has a curvature radius of -80 mm and a diameter of 15 mm; the 1.94 µm second plano-convex lens (2-5) and the 1.94 µm third plano-convex lens (2-6) are coated with 1.94 µm anti-reflection film on both surfaces, the focal length is 80 mm-200 mm, and the diameter is 15 mm; the 1.94 µm half-wave plate (2-2) is coated with 1.94 µm anti-reflection film on both surfaces, the thickness is 0.1 mm, and the diameter is 15 mm.

10. The compact mid-long wave infrared solid state laser of claim 7, wherein, The 45° 1.94 µm full reflection mirror (2-3) is coated with 793 nm anti-reflection film on both sides, the reflecting surface is coated with 1.94 µm full reflection film, and the diameter is 15 mm. The 45° 1.94 µm polaroid (2-4) is coated with 1.94 µm polaroid film on the reflecting surface and 1.94 µm anti-reflection film on the transmitting surface, and the diameter is 15 mm. The first 45° middle wave infrared reflecting mirror (2-7), the second 45° middle wave infrared reflecting mirror (2-8), and the third 45° middle wave infrared reflecting mirror (2-10) are coated with 1.94 µm anti-reflection film and 6.2 µm anti-reflection film on both sides, the reflecting surface is coated with 45° 2.8 µm full reflection film, and the diameter is 15 mm. The ZGP crystal (2-9) is coated with 1.94 µm anti-reflection film, 6.2 µm anti-reflection film, and 2.8 µm anti-reflection film on both sides, and the length is 30 mm. The 45° middle wave infrared output coupling lens (2-11) is coated with 1.94 µm anti-reflection film and 6.2 µm anti-reflection film on both sides, the reflecting surface is coated with 2.8 µm transmission rate 40%~50% film layer, and the diameter is 15 mm.

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