Apparatus and method for generating a wide-tunable narrow linewidth mid-infrared laser

Abstract

The application relates to the field of laser technology, in particular to a device and a method for generating wide-tuning narrow-line-width mid-infrared laser, wherein the pump light emitted by a nanosecond pulse OPO base frequency pump source is reflected to a beam splitter by a full reflection mirror after passing through a first adjuster; the pump light emitted by a continuous wave OPO base frequency pump source is irradiated to the beam splitter after passing through a second adjuster; the two beams of pump light are combined after passing through the beam splitter, are focused after passing through a plano-convex lens, are irradiated to a first plano-concave full reflection mirror, and then are transmitted to a nonlinear crystal to generate signal light and idler mid-infrared laser through nonlinear frequency conversion; the idler mid-infrared laser and the residual pump light are transmitted to a doublet mirror and are separated by the doublet mirror; the signal light is reflected to the nonlinear crystal in sequence through a second plano-concave full reflection mirror, a first plane full reflection mirror, a second plane full reflection mirror and the first plano-concave full reflection mirror, and an oscillation closed loop is formed. The application realizes that the pulse OPO outputs a pulse with a line width less than 90 MHz in the tuning range, and the extraction efficiency of the idler light is as high as 9.3%.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of laser technology, in particular to a device and method for generating wide-tunable narrow-linewidth mid-infrared laser. BACKGROUND

[0002] With the continuous evolution of technologies such as laser radar, high spectral resolution spectral detection in recent years, the demand for high peak power, wide frequency coverage, narrow linewidth high performance laser light source is increasing, especially in the mid-infrared (MIR) region, the applicable laser light source is even scarce. As a general means of generating tunable coherent radiation, the optical parametric oscillator (OPO) continues to play its advantages in spectral regions where traditional lasers cannot work to generate coherent radiation. However, for a free-running pulsed OPO, there is a fixed limit to the minimum spectral width it can obtain, that is, the full width at half maximum (FWHM) of the spectral bandwidth is not less than the relevant Fourier transform limit.

[0003] Although the pulsed OPO can obtain narrow linewidth output by using gratings or etalons and other wavelength selection elements in the cavity, when the system needs to be tuned, complex technology is needed to maintain single-mode operation. Another method to obtain narrow linewidth laser output from a pulsed nanosecond OPO is to use seed injection technology. The significant advantage of this method is to simplify the structure of the OPO, and there is no need for a complex oscillation cavity to limit the oscillation bandwidth. So far, there have been many studies on nanosecond pulsed OPOs, successfully using various light sources for seed injection. However, most of the research is carried out under the condition of fixed wavelength seed laser, and cannot effectively work on the entire tuning range of the OPO. Recently, Opt. Lett. reported a form of sharing the same resonant cavity by a nanosecond OPO and a continuous OPO to obtain wide-tunable narrow-linewidth mid-infrared output. However, this method requires the use of two nonlinear crystals and separate temperature control to achieve mode matching of the seed light and the slave laser, thus increasing the complexity of the system. SUMMARY

[0004] In order to overcome the deficiencies of the prior art, the purpose of the present application is to provide a device and method for generating wide-tunable narrow-linewidth mid-infrared laser, which can obtain wide-tunable narrow-linewidth mid-infrared laser while reducing the complexity of the system through a compact, efficient and simplified intra-cavity seed injection structure.

[0005] In order to achieve the above object, the technical scheme of the present application is a device for generating wide-tuning narrow-line-width mid-infrared laser, comprising a nanosecond pulse OPO fundamental frequency pump source, a first adjuster, a total reflection mirror, a continuous wave OPO fundamental frequency pump source, a second adjuster, a beam splitter, a plano-convex lens, a dichroic mirror and an OPO ring cavity; the OPO ring cavity comprises a first plano-concave total reflection mirror, a second plano-concave total reflection mirror, a first plane total reflection mirror, a second plane total reflection mirror and a nonlinear crystal; the nanosecond pump light emitted by the nanosecond pulse OPO fundamental frequency pump source is adjusted in power and polarization direction by the first adjuster, and then reflected to the beam splitter by the total reflection mirror; the continuous pump light emitted by the continuous wave OPO fundamental frequency pump source is adjusted in power and polarization direction by the second adjuster, and then irradiated to the beam splitter; after the two pump lights are combined by the beam splitter, they are focused by the plano-convex lens and then irradiated to the first plano-concave total reflection mirror, and then enter the nonlinear crystal to generate signal light and idler mid-infrared laser through nonlinear frequency conversion; the idler mid-infrared laser and the remaining pump light are transmitted to the dichroic mirror by the second plano-concave total reflection mirror and separated by the dichroic mirror; the signal light is reflected to the nonlinear crystal by the second plano-concave total reflection mirror, the first plane total reflection mirror, the second plane total reflection mirror and the first plano-concave total reflection mirror in turn, forming an oscillation closed loop.

[0006] Optimally, the nonlinear crystal is placed in a temperature control furnace and is placed as a whole on a horizontal sliding table.

[0007] Optimally, the first adjuster and the second adjuster are the same in structure and each comprises a first half-wave plate, a polarization beam splitter and a second half-wave plate arranged in sequence.

[0008] Optimally, the nanosecond pulse OPO fundamental frequency pump source is a Q-switched semiconductor laser with an output power of 30 W, a pulse width of 2-26 ns, a repetition frequency of 20-100 kHz and a center wavelength of 1064 nm.

[0009] Optimally, the continuous wave OPO fundamental frequency pump source is a continuous ytterbium-doped fiber laser with an output power of 30 W, a line width less than 90 kHz and a center wavelength of 1064.1 nm.

[0010] Optimally, the nonlinear crystal is a 5% MgO:PPLN with a length of 38 mm and a thickness of 1 mm, a grating polarization period of 29.5-31.5 μm and a period step of 0.5 μm.

[0011] Optimally, the first plano-concave total reflection mirror and the second plano-concave total reflection mirror each have a curvature radius of 150 mm.

[0012] Optimally, the first flat concave total reflection mirror, the second flat concave total reflection mirror, the first flat total reflection mirror and the second flat total reflection mirror are all coated, and the transmittance T of the pump 1064 nm is greater than 90%, the transmittance T in the 2-4 mu m spectral range is greater than 80%, and the reflectivity R in the 1.3-1.9 mu m spectral range is greater than 99%.

[0013] The embodiment also provides a method for outputting a wide-tuning narrow-line-width mid-infrared laser by using the device.

[0014] S1, the nanosecond pump light emitted by the nanosecond pulse OPO base frequency pump source is irradiated to the total reflection mirror after the power and the polarization direction are adjusted by the first adjuster, and is reflected to the beam splitter by the total reflection mirror; the continuous wave OPO base frequency pump source emits continuous pump light, which is irradiated to the beam splitter after the power and the polarization direction are adjusted by the second adjuster;

[0015] S2, after the two beams of pump light are combined by the beam splitter, the pump light is irradiated to the first flat concave total reflection mirror after being focused by the plano-convex lens, and then enters the nonlinear crystal to generate signal light and idler mid-infrared laser through nonlinear frequency conversion;

[0016] S3, the idler mid-infrared laser and the remaining pump light are transmitted to the dichroic mirror by the second flat concave total reflection mirror and are separated by the dichroic mirror; the signal light is reflected to the nonlinear crystal in turn by the second flat concave total reflection mirror, the first flat total reflection mirror, the second flat total reflection mirror and the first flat concave total reflection mirror, forming an oscillation closed loop.

[0017] Optimally, by adjusting the position of the nonlinear crystal, different grating polarization periods are selected, and / or by adjusting the temperature of the nonlinear crystal, signal light and idler mid-infrared laser of a certain wavelength are obtained.

[0018] Compared with the prior art, the present application has the following beneficial effects:

[0019] (1) The present application uses a single-resonance continuous OPO as a seed laser, and the seed laser is injected into the nanosecond pulse OPO cavity through a compact, efficient and simplified intra-cavity seed injection structure, so that a device capable of obtaining wide-tuning range, narrow-line-width mid-infrared laser while reducing the complexity of the system is obtained.

[0020] (2) The present application realizes that the pulse OPO has a line width less than 90MHz in its tuning range, the extraction efficiency of idler light is as high as 9.3%, the power is increased by ~3.8 times, and the power stability is good.

[0021] (3) The method of the present application has a greatly shortened line width and a significantly improved efficiency compared with a free-running nanosecond pulse optical parametric oscillator, and can be applied to a laser system requiring a narrow-line-width, wide-tuning pulse optical parametric oscillator. BRIEF DESCRIPTION OF DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the accompanying drawings needed to be used in the embodiments or prior art description will be briefly introduced. Obviously, the accompanying drawings in the following description only represent some embodiments of the present application, and all other drawings obtained by those of ordinary skill in the art without creative effort based on these drawings belong to the protection scope of the present application.

[0023] Figure 1 The optical path schematic diagram of the device for generating a wide-tuning narrow-line-width mid-infrared laser provided by the embodiments of the present application;

[0024] Figure 2 The pulse OPO tuning curve, wherein the circle points are measured data, and the solid line is obtained by theoretical calculation;

[0025] Figure 3 The pulse nanosecond OPO power curve when the seed is injected (solid) and when it is free running (hollow);

[0026] Figure 4 The measured spectrum when the pulse OPO is free running (a), and the spectrum width obtained by the Bragg-Pauli interferometer when the seed is injected (b);

[0027] In the figure: 1, nanosecond pulse OPO fundamental frequency pump source; 2, continuous wave OPO fundamental frequency pump source; 3, first half-wave plate; 4, polarization beam splitter; 5, second half-wave plate; 6, total reflection mirror; 7, beam splitter; 8, plano-convex lens; 9, first plano-concave total reflection mirror; 10, nonlinear crystal; 11, second plano-concave total reflection mirror; 12, first plane total reflection mirror; 13, second plane total reflection mirror; 14, dichroic mirror. DETAILED DESCRIPTION

[0028] The technical solutions in the embodiments of the present application will be described clearly and completely in combination with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments only represent some embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort belong to the protection scope of the present application.

[0029] As Figure 1As shown, the embodiment provides a device for generating wide-tuning narrow-line-width mid-infrared laser, which comprises a nanosecond pulse OPO fundamental frequency pump source 1, a first adjuster, a total reflection mirror 6, a continuous wave OPO fundamental frequency pump source 2, a second adjuster, a beam splitter 7, a plano-convex lens 8, a dichroic mirror 14 and an OPO ring cavity; the OPO ring cavity comprises a first plano-concave total reflection mirror 9, a second plano-concave total reflection mirror 11, a first plane total reflection mirror 12, a second plane total reflection mirror 13 and a nonlinear crystal 10; the nanosecond pump light emitted by the nanosecond pulse OPO fundamental frequency pump source 1 is adjusted in power and polarization direction by the first adjuster, and then reflected to the beam splitter 7 by the total reflection mirror 6; the continuous pump light emitted by the continuous wave OPO fundamental frequency pump source 2 is adjusted in power and polarization direction by the second adjuster, and then irradiated to the beam splitter 7; after the two pump lights are combined by the beam splitter 7, they are focused by the plano-convex lens 8 and then irradiated to the first plano-concave total reflection mirror 9, and then enter the nonlinear crystal 10 to generate signal light and idler mid-infrared laser through nonlinear frequency conversion; the idler mid-infrared laser and the remaining pump light are transmitted to the dichroic mirror 14 by the second plano-concave total reflection mirror 11 and separated by the dichroic mirror 14; the signal light is reflected to the nonlinear crystal 10 by the second plano-concave total reflection mirror 11, the first plane total reflection mirror 12, the second plane total reflection mirror 13 and the first plano-concave total reflection mirror 9 in turn, forming an oscillation closed loop. The embodiment adopts a stable single-frequency continuous light OPO as a seed laser, which is injected into the nanosecond pulse OPO cavity through a compact, efficient and simplified intra-cavity seed injection structure, so that narrow-band laser output with a bandwidth less than 90 MHz in the tuning range of the pulse OPO can be obtained. While obtaining wide-tuning range and narrow-line-width mid-infrared laser, the conversion efficiency is also significantly improved, and the complexity of the system is reduced.

[0030] Optimally, the nonlinear crystal 10 is placed in a temperature-controlled furnace and is placed as a whole on a horizontal sliding table. The adjustment accuracy of the temperature-controlled furnace is ±0.1 0 C, and the adjustment range is 25-200 0 C. The embodiment places the nonlinear crystal 10 on a precise horizontal sliding table, which can be well adjusted in the horizontal position, so that different grating polarization periods can be selected for the purpose of coarse tuning; by changing the temperature setting of the nonlinear crystal 10, the purpose of fine wavelength tuning can be further achieved. The continuous wave and nanosecond pulse pump radiation are respectively focused at the center of the nonlinear crystal 10, and the total optical length of the OPO cavity is about 100 cm.

[0031] Optimally, the first adjuster and the second adjuster are the same in structure, and each comprises a first half-wave plate 3, a polarization beam splitter 4 and a second half-wave plate 5 arranged in sequence. As Figure 1As shown, the first adjuster and the second adjuster of the embodiment are both used for adjusting the power and the polarization direction of the incident light, and have the same structure, the first half-wave plate 3, the polarization beam splitter 4 and the second half-wave plate 5 are arranged on the same straight line; wherein the first half-wave plate 3 and the polarization beam splitter 4 are used for adjusting the power of the incident light, and the power of the incident light is controlled by rotating the first half-wave plate 3; the second half-wave plate 5 is used for adjusting the deflection angle of the incident light.

[0032] Optimally, the nanosecond pulse OPO fundamental pump source 1 is a Q-switched semiconductor laser, the output power is 30W, the pulse width is 2-26 ns, the repetition frequency is 20-100 kHz, and the center wavelength is 1064 nm.

[0033] Optimally, the continuous wave OPO fundamental pump source 2 is a continuous wave ytterbium-doped fiber laser, the output power is 30W, the line width is less than 90 kHz, and the center wavelength is 1064.1 nm.

[0034] In the embodiment, the total reflection mirror 6 and the beam splitter 7 are arranged in parallel and are both arranged at 45°; the pump light emitted by the nanosecond pulse OPO fundamental pump source 1 is irradiated on the total reflection mirror 6 at an angle of 45° after the power and the polarization direction are adjusted, is reflected by the total reflection mirror 6 at an angle of 45°, and is reflected by the beam splitter 7; the pump light emitted by the continuous wave OPO fundamental pump source 2 is irradiated on the beam splitter 7 at an angle of 45° after the power and the polarization direction are adjusted, and is transmitted by the beam splitter 7; the two beams of pump light are combined after passing through the beam splitter 7, at this time, the maximum pump power of the continuous wave and the nanosecond pulse OPO is 20W and 5W respectively. The nanosecond pulse light beam and the continuous wave light beam are combined and focused on the center of the nonlinear crystal 10 in the OPO cavity by using the plano-convex lens 8.

[0035] Optimally, the curvature radius of the first plano-concave total reflection mirror 9 and the second plano-concave total reflection mirror 11 is 150 mm, and the concave surface faces the nonlinear crystal 10. The beam splitter 7, the plano-convex lens 8, the first plano-concave total reflection mirror 9, the nonlinear crystal 10, the second plano-concave total reflection mirror 11 and the dichroic mirror 14 are sequentially arranged and on the same straight line; the first plane total reflection mirror 12 and the second plane total reflection mirror 13 are on the same straight line.

[0036] Optimally, the first plano-concave total reflection mirror 9, the second plano-concave total reflection mirror 11, the first plane total reflection mirror 12 and the second plane total reflection mirror 13 are all coated, and the transmittance T of the pump 1064 nm is greater than 90%, the transmittance T in the 2-4 µm spectral range is greater than 80%, and the reflectivity R in the 1.3-1.9 µm spectral range is greater than 99%, which ensures that the oscillator is single-resonant oscillation.

[0037] Optimally, the nonlinear crystal 10 adopts 5% MgO:PPLN with a length of 38 mm and a thickness of 1 mm, a grating polarization period of 29.5-31.5 μm, and a period step of 0.5 μm. The end face of the nonlinear crystal 10 of the embodiment is coated with a transmission film of three wavebands of pump, signal, and idler waves.

[0038] The embodiment also provides a method for outputting a wide-tunable narrow-line-width mid-infrared laser by using the above device, characterized by comprising the following steps:

[0039] S1, the nanosecond pump light emitted by the nanosecond pulse OPO fundamental pump source 1 is irradiated onto the total reflection mirror 6 after being adjusted in power and polarization direction by the first adjuster, and is reflected by the total reflection mirror 6 to the beam splitter 7; the continuous wave OPO fundamental pump source 2 emits continuous pump light which is irradiated onto the beam splitter 7 after being adjusted in power and polarization direction by the second adjuster;

[0040] S2, the two beams of pump light are combined after passing through the beam splitter 7, are focused by the plano-convex lens 8, and are then irradiated onto the first plano-concave total reflection mirror 9, and then are incident into the nonlinear crystal 10 to generate signal light and idler mid-infrared laser through nonlinear frequency conversion;

[0041] S3, the idler mid-infrared laser and the remaining pump light are transmitted through the second plano-concave total reflection mirror 11 to the dichroic mirror 14 and are separated by the dichroic mirror 14; the signal light is reflected by the second plano-concave total reflection mirror 11, the first plane total reflection mirror 12, the second plane total reflection mirror 13, and the first plano-concave total reflection mirror 9 in turn to the nonlinear crystal 10, forming an oscillation closed loop. The method of the embodiment realizes the output of a pulse OPO with a line width less than 90 MHz in its tuning range, the extraction efficiency of idler light is as high as 9.3%, the power is increased by ~3.8 times, and the power stability is good.

[0042] Optimally, the nonlinear crystal 10 is placed in a temperature control furnace and is placed on a horizontal sliding table as a whole. The adjustment accuracy of the temperature control furnace is ±0.1 0 C, and the adjustment range is 25-200 0 C; different grating polarization periods can be selected by adjusting the position of the nonlinear crystal 10, and / or the temperature of the nonlinear crystal 10 is adjusted by the temperature control furnace, so as to obtain signal light and idler mid-infrared laser of a certain wavelength. By changing the phase matching condition, i.e., changing the crystal temperature and / or the grating polarization period, the OPO can convert the pump light into tunable coherent laser output. Figure 2 The wavelength of the PPLN OPO with a grating polarization period of 31 μm changes with the crystal temperature, wherein the solid curve is a tuning curve calculated according to the Sellmeier equation, the solid circles represent the actual measurement data, and the coincidence of the solid circles and the solid curve also proves the coincidence between the experimental results and the theoretical calculation results. From the figure, it can be seen that the wavelength of the PPLN OPO changes with the crystal temperature, and the wavelength of the signal light and the idler mid-infrared laser can be adjusted by changing the crystal temperature. Figure 2It can be seen that, by changing the crystal temperature from 20 0 C to 200 0 C, the OPO can obtain continuously tunable 1591-1711 nm signal light and 2814-3213 nm idler mid-infrared laser. Although Figure 2 the lowest temperature of the OPO operation is shown in the middle at 57℃, in actual operation, the OPO can operate at room temperature, and the difference between the theoretical temperature and the experimental temperature is due to the temperature rise in the crystal caused by the absorption of the pump light by the crystal, and the corresponding phase matching temperature can be obtained by adjusting the temperature of the corresponding temperature control furnace.

[0043] When the OPO pumped by the pulsed laser is above the oscillation threshold, since the high gain oscillator will be in a multimode simultaneous oscillation state, the signal and idler light output by the free-running nanosecond pulse OPO is usually a multimode broadband output. However, this can be overcome by injecting a narrow linewidth laser, as long as its frequency coincides with the cavity mode (or modes) of the OPO. If the intensity of the injected radiation is significantly greater than the pulsed parametric noise light, at this time the OPO will mainly oscillate on the injected cavity mode, which means that the build-up time of the injection cavity mode will be significantly reduced when the seed injection is running. Therefore, the threshold of the nanosecond pulse OPO when the seed is injected will be lowered, and the total power of the seed-injected pulse OPO will be higher than that of the free-running. In the experiment, a nanosecond pump light with an average power of 4.85 W and a pulse width of 12.6 ns was used to pump the OPO, the working temperature of the nonlinear crystal 10 was set to 70℃, and the grating polarization period was 31µm, which corresponds to the idler light wavelength of 3200 nm and the signal light wavelength of 1613 nm; when the continuous pump light is also injected into the resonant cavity, that is, the continuous wave OPO and the nanosecond pulse OPO work at the same time, which means that the nanosecond pulse OPO is injected with a seed, at this time the threshold of the nanosecond pulse OPO is lowered, and the pulsed laser output power is also increased compared with the free-running, and the results are shown in Figure 3 The OPO threshold under seed injection is reduced from 1.8 W to about 1 W, and when the maximum pump power is 4.85 W, the maximum power of the free-running nanosecond OPO is 150 mW; with the continuous wave OPO working at the same time, an additional 390 mW of idler mid-infrared laser is generated, which corresponds to an idler light conversion efficiency of about 9.3%, so the conversion efficiency of the OPO when the seed is injected is improved by 6.2% compared with the free-running.

[0044] Furthermore, when continuous wave OPO and nanosecond pulsed OPO operate simultaneously, the non-seeded longitudinal modes of all freely moving nanosecond pulsed OPOs are significantly suppressed, while the longitudinal modes matching the seed wavelength are enhanced. Therefore, a narrow linewidth pulse output can be obtained during seed injection. In the experiment, the linewidths of the nanosecond pulsed OPO signal light during free movement and seed injection were measured to be 4.43 nm and 90 MHz, respectively. Clearly, the linewidth is significantly compressed by several orders of magnitude, thus achieving a very good narrow linewidth output effect. The experimental results are as follows: Figure 4 As shown. It should be noted that, due to a measured difference of 0.25 nm between the center wavelength of the nanosecond laser and the center wavelength of the continuous wave, the generated signal light exhibits a measured separation of 0.51 nm (limited by the instrument's resolution). Therefore, the seed wavelength is actually injected into the flank of the pulsed OPO gain curve, rather than at the maximum gain, yet a good spectral width compression effect is still achieved. Therefore, by optimizing the pump wavelength to match the signal light wavelengths of both the continuous wave and the pulsed light, the optimal compression effect can be further obtained.

[0045] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An apparatus for generating a wide-tunable narrow-linewidth mid-infrared laser, characterized by: The OPO ring cavity comprises a first plano-concave total reflection mirror, a second plano-concave total reflection mirror, a first plane total reflection mirror, a second plane total reflection mirror and a nonlinear crystal; the nanosecond pulse OPO fundamental frequency pump source emits nanosecond pump light, which is adjusted in power and polarization direction by the first adjuster, and then reflected to the beam splitter by the total reflection mirror; the continuous wave OPO fundamental frequency pump source emits continuous pump light, which is adjusted in power and polarization direction by the second adjuster and then irradiated to the beam splitter; after the two beams of pump light are combined by the beam splitter, they are focused by the plano-convex lens and then irradiated to the first plano-concave total reflection mirror, and then enter the nonlinear crystal to generate signal light and idler mid-infrared laser through nonlinear frequency conversion; the idler mid-infrared laser and the remaining pump light are transmitted to the dichroic mirror by the second plano-concave total reflection mirror and separated by the dichroic mirror; the signal light is reflected to the nonlinear crystal in turn by the second plano-concave total reflection mirror, the first plane total reflection mirror, the second plane total reflection mirror and the first plano-concave total reflection mirror, forming an oscillation closed loop; the end face of the nonlinear crystal is coated with a transmission film of three wavebands of pump, signal and idler; The curvature radii of the first plano-concave total reflection mirror and the second plano-concave total reflection mirror are both 150 mm; the nanosecond pulse OPO fundamental frequency pump source is a Q-switched semiconductor laser, with an output power of 30 W, a pulse width of 2-26 ns, a repetition frequency of 20-100 kHz and a center wavelength of 1064 nm; the continuous wave OPO fundamental frequency pump source is a continuous ytterbium-doped fiber laser, with an output power of 30 W, a line width less than 90 kHz and a center wavelength of 1064.1 nm; the nonlinear crystal adopts 5% MgO:PPLN with a length of 38 mm and a thickness of 1 mm, a grating polarization period of 29.5-31.5 μm and a period step of 0.5 μm.

2. A device for generating a mid-infrared laser with a wide tuning range and a narrow linewidth as claimed in claim 1, characterized in that: The nonlinear crystal is placed in a temperature control furnace and is integrally placed on a horizontal sliding table.

3. A device for generating a mid-infrared laser with a wide tuning range and a narrow linewidth as claimed in claim 1, characterized in that: The first adjuster and the second adjuster are the same in structure and both comprise a first half-wave plate, a polarization beam splitter and a second half-wave plate arranged in sequence.

4. A device for generating a mid-infrared laser with a wide tuning range and a narrow linewidth as claimed in claim 1, characterized in that: The first plano-concave total reflection mirror, the second plano-concave total reflection mirror, the first plane total reflection mirror and the second plane total reflection mirror are all coated, and the transmittance T of pump 1064 nm is greater than 90%, the transmittance T in the spectral range of 2-4 μm is greater than 80%, and the reflectance R in the spectral range of 1.3-1.9 μm is greater than 99%.

5. A method for outputting a mid-infrared laser with a wide tuning and a narrow linewidth by using the apparatus according to any one of claims 1-4, characterized in that, The method comprises the following steps: S1, the nanosecond pump light emitted by the nanosecond pulse OPO fundamental frequency pump source is irradiated to the total reflection mirror after being adjusted in power and polarization direction by the first adjuster, and then reflected to the beam splitter by the total reflection mirror; the continuous pump light emitted by the continuous wave OPO fundamental frequency pump source is irradiated to the beam splitter after being adjusted in power and polarization direction by the second adjuster; S2, after the two beams of pump light are combined by the beam splitter, they are focused by the plano-convex lens and then irradiated to the first plano-concave total reflection mirror, and then enter the nonlinear crystal to generate signal light and idler mid-infrared laser through nonlinear frequency conversion; S3, the idler mid-infrared laser and the residual pump light are transmitted to the dichroic mirror through the second plano-concave total reflection mirror and separated by the dichroic mirror; the signal light is reflected to the nonlinear crystal by the second plano-concave total reflection mirror, the first plane total reflection mirror, the second plane total reflection mirror and the first plano-concave total reflection mirror in turn, forming an oscillation closed loop.

6. The method of claim 5, wherein the outputting a mid-infrared laser with a wide tuning and a narrow linewidth comprises: outputting a mid-infrared laser with a wide tuning and a narrow linewidth by using a quantum cascade laser with a distributed feedback structure. By adjusting the position of the nonlinear crystal to select different grating polarization periods, and / or by adjusting the temperature of the nonlinear crystal, signal light and idler mid-infrared laser of a certain wavelength are obtained.

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