High-efficiency, compact, and debug-free mid-infrared 4μm band solid-state laser

Abstract

The present invention relates to solid-state lasers, and specifically to a high-efficiency, compact, and debug-free mid-infrared 4μm band solid-state laser. This laser is designed to address the shortcomings of current mid-infrared 4μm band solid-state lasers, such as their high reliance on liquid nitrogen refrigeration, which limits their scope of use and poor portability. Furthermore, the use of coated lenses in the resonant cavity increases the difficulty of laser cavity debugging and increases laser oscillation loss, reducing laser operating efficiency and leading to poor laser stability. This high-efficiency, compact, and debug-free mid-infrared 4μm band solid-state laser proposes, for the first time, the use of an electric refrigerator to achieve a low temperature below 100K to cool the laser crystal to produce continuous laser output in the mid-infrared 4μm band. This addresses the current high reliance of mid-infrared 4μm band solid-state lasers on liquid nitrogen refrigeration conditions, reduces the laser's requirements for operating conditions, and significantly improves the laser's applicability and portability.

Description

Technical Field

[0001] The invention relates to a solid-state laser, in particular to a high-efficiency, compact, debugging-free mid-infrared 4μm band solid-state laser. Background Art

[0002] The 3-5 μm band is within the atmospheric transmission window, and its ideal atmospheric transmission characteristics make lasers in this band widely used in fields such as spectroscopy, environmental pollution monitoring, sensing, medical treatment, and optoelectronic countermeasures. Due to the enormous application value of lasers in this band, gas lasers, chemical lasers, fiber lasers, optical parametric oscillators, quantum cascade semiconductor lasers, and solid-state lasers have all demonstrated significant development potential in laser generation in this band. Compared to other lasers, solid-state laser devices using transition metal iron ions doped with II-VI group sulfide crystals (ZnSe or ZnS crystals) as gain media can achieve mid-infrared 4 μm band laser output. These devices have the advantages of high conversion efficiency, wide wavelength tuning range, good power stability, scalable amplification, and compact structure, making them one of the effective technical approaches currently available for achieving high-power tunable laser output in the mid-infrared band. However, the upper energy level lifetime of iron ions in sulfide crystals is only 0.37 μs at room temperature, but can reach 57 μs at low temperatures (77 K). Therefore, continuous laser output in the 4 μm band is difficult to achieve at room temperature. To achieve high-efficiency continuous laser output in the 4 μm band, the laser crystal must be cooled to below 100 K, typically using liquid nitrogen. In 2012, Evans et al. used a 2.94 μm solid-state Er:YAG laser to pump an iron-doped zinc selenide crystal, achieving 840 mW continuous-wave laser output in the 4 μm band at 77 K, with a light-to-light conversion efficiency of 28% ("840 mW continuous-wave Fe:ZnSe laser operating at 4140 nm" in Optics Letters, Vol. 37, 2012). In 2018, Pushkin et al. used a 2.8μm fiber laser to pump an Fe:ZnSe crystal, achieving a 4μm continuous-wave laser output with a power of 2.1W under liquid nitrogen refrigeration conditions, with an optical-to-optical conversion efficiency of up to 32% (“Compact, highly efficient, 2.1-W continuous-wave mid-infrared Fe:ZnSe coherent source, pumped by an Er:ZBLAN fiber laser” in Optics Letters, Vol. 43, 2018). These lasers all use 3μm-band solid-state or fiber lasers to pump Fe:ZnSe crystals to produce mid-infrared 4μm laser output. However, they suffer from two common problems: First, the laser crystal is cooled by liquid nitrogen, resulting in a complex overall structure and a high dependence on refrigeration conditions. Without liquid nitrogen, the laser cannot operate, resulting in poor portability. Second, the resonant cavity uses coated lenses, which not only increases the difficulty of laser resonator debugging and increases laser oscillation losses, reducing laser efficiency, but also poorly stabilizes the entire laser system. Summary of the Invention

[0003] The purpose of the present invention is to solve the shortcomings of the current mid-infrared 4μm band solid-state laser, such as its high reliance on liquid nitrogen refrigeration, which limits its scope of use and poor portability, and the use of coated lenses in the resonant cavity, which not only increases the difficulty of laser cavity debugging and laser oscillation loss, but also reduces the laser working efficiency and leads to poor laser stability. The present invention provides a high-efficiency, compact, and debug-free mid-infrared 4μm band solid-state laser.

[0004] The present invention provides the following technical solutions:

[0005] A high-efficiency, compact, debug-free mid-infrared 4μm band solid-state laser, which is special in that it includes a first pump source, a low-temperature electric refrigerator, and a first focusing lens and a laser crystal arranged in sequence along the optical path of the first pump source;

[0006] The temperature range of the cooling head of the low-temperature electric refrigerator is 40-100K. The cooling head is arranged in a vacuum chamber. The laser crystal is located in the vacuum chamber and is placed on the cooling head after being wrapped with a copper heat sink. Two light-transmitting windows are provided at the intersection of the vacuum chamber and the optical path of the first pump source. The laser crystal is provided with a first end face and a second end face at the intersection of the optical path of the first pump source. The first end face and the second end face are respectively coated with a fully reflective dielectric film B and an output dielectric film C. The fully reflective dielectric film B has a transmittance of ≥95% for the pump light of the first pump source and a reflectance of ≥98% for the laser light in the 4μm band. The output dielectric film C has a transmittance of ≥95% for the pump light of the first pump source and a reflectance of 10-90% for the laser light in the 4μm band.

[0007] The pump light of the first pump source is focused by the first focusing lens, and is incident on the first end face or the second end face of the laser crystal to generate 4μm band laser light, which is then emitted from the second end face;

[0008] The 4 μm band laser is a laser with a wavelength of 3.8 to 5 μm.

[0009] Furthermore, the first pump source is a laser with a wavelength in the range of 2.5 to 3.4 μm.

[0010] Furthermore, the laser crystal is an iron-doped sulfide crystal, wherein the iron ion doping concentration range is 0.5×10 18 cm -3 ~50×10 18 cm -3 ; The base material of the laser crystal is one of zinc selenide (ZnSe), zinc sulfide (ZnS), zinc telluride (ZnTe) and cadmium selenide (CdSe).

[0011] Furthermore, the material of the two light-transmitting windows is one of calcium fluoride (CaF2), magnesium fluoride (MgF2), and zinc selenide (ZnSe), and both light-transmitting windows are coated with a dielectric film A, and the transmittance of the dielectric film A for 2.5-5μm band laser is ≥95%.

[0012] Furthermore, the first focusing lens is a CaF2 lens with a focal length range of 25 to 200 mm.

[0013] Furthermore, a plane dichroic mirror is arranged between the first pump source and the first focusing lens. The angle between the plane dichroic mirror and the pump light of the first pump source is 45°. The transmittance of the plane dichroic mirror to the pump light of the first pump source is ≥95%, and the reflectivity of the plane dichroic mirror to the 4μm band laser is ≥99%; the pump light of the first pump source passes through the plane dichroic mirror and is incident from the second end face of the laser crystal to generate 4μm band laser. The 4μm band laser is emitted from the second end face, and then is focused by the first focusing lens and reflected by the plane dichroic mirror before being output.

[0014] Furthermore, it also includes a second pumping source and a second focusing lens, wherein the second pumping source and the first pumping source are arranged opposite to each other and their optical paths overlap, and the second focusing lens is arranged between the second pumping source and the laser crystal, and the pumping light of the second pumping source is incident on the first end face to generate 4μm band laser light, and the 4μm band laser light is emitted from the second end face;

[0015] The transmittance of the fully reflective dielectric film B and the output dielectric film C to the pump light of the second pump source is ≥95%;

[0016] The second focusing lens is a CaF2 lens with a focal length ranging from 25 to 200 mm.

[0017] At the same time, the present invention also provides a high-efficiency, compact, debugging-free mid-infrared 4μm band solid-state laser, which is special in that it includes a first pump source, a second pump source, a polarization beam splitter, a low-temperature electric refrigerator, a first focusing lens, and a laser crystal;

[0018] The temperature range of the cooling head of the low-temperature electric refrigerator is 40-100K. The cooling head is arranged in a vacuum chamber. The laser crystal is located in the vacuum chamber and is arranged on the cooling head after being wrapped with a copper heat sink.

[0019] The second pump source optical path is perpendicular to the first pump source optical path, the first pump source is P-polarized, and the second pump source is S-polarized; the polarization beam splitter is arranged at the intersection of the optical paths of the first pump source and the second pump source, and is used to combine the pump light of the first pump source and the second pump source to form a combined beam; the first focusing lens and the laser crystal are arranged in sequence along the combined beam path;

[0020] Two light-transmitting windows are provided at the intersection of the vacuum chamber and the combined light path; a first end face and a second end face are provided at the intersection of the laser crystal and the combined light path, respectively, and the first end face and the second end face are respectively coated with a fully reflective dielectric film B and an output dielectric film C; the fully reflective dielectric film B has a transmittance of ≥95% for the combined light and a reflectance of ≥98% for 4μm laser; the output dielectric film C has a transmittance of ≥95% for the combined light and a reflectance of 10-90% for 4μm laser.

[0021] The combined light is focused by the first focusing lens, and is incident on the first end face of the laser crystal to generate 4μm band laser light, which is then emitted from the second end face;

[0022] The 4 μm band laser is a laser with a wavelength of 3.8 to 5 μm.

[0023] Furthermore, the first pump source and the second pump source are lasers with wavelengths in the range of 2.5 to 3.4 μm; the laser crystal is an iron-doped sulfide crystal, wherein the iron ion doping concentration range is 0.5×10 18 cm -3 ~50×10 18 cm -3 ; The base material of the laser crystal is one of zinc selenide, zinc sulfide, zinc telluride and cadmium selenide.

[0024] Furthermore, the material of the two light-transmitting windows is one of calcium fluoride, magnesium fluoride, and zinc selenide, and both light-transmitting windows are coated with a dielectric film A, and the transmittance of the dielectric film A for 2.5-5μm band laser is ≥95%; the first focusing lens uses a CaF2 lens with a focal length range of 25-200mm.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] (1) The high-efficiency, compact, and debug-free mid-infrared 4μm band solid-state laser of the present invention proposes for the first time the use of an electric refrigerator to obtain a low temperature below 100K to cool the laser crystal, so as to produce a continuous laser output in the mid-infrared 4μm band. This solves the problem that the current mid-infrared 4μm band solid-state laser is highly dependent on liquid nitrogen refrigeration conditions, reduces the requirements of the laser on working conditions, and greatly improves the applicability and portability of the laser.

[0027] (2) The high-efficiency, compact, and adjustment-free mid-infrared 4μm band solid-state laser of the present invention directly plates the resonant cavity film system on the laser crystal, which not only eliminates the manual alignment and adjustment process of the mid-infrared solid-state laser resonant cavity, but also reduces the laser resonant cavity loss, realizes the miniaturization of the laser resonant cavity, and has higher laser efficiency, simple overall structure, convenient operation, good stability, and is easy to miniaturize. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic structural diagram of a first embodiment of the high-efficiency, compact, debug-free mid-infrared 4μm band solid-state laser according to the present invention;

[0029] Figure 2 This is a structural diagram of embodiment 2 of the present invention;

[0030] Figure 3 This is a schematic structural diagram of embodiment 3 of the present invention;

[0031] Figure 4 This is a schematic diagram of the structures of Embodiments 4 to 6 of the present invention.

[0032] The reference numerals are as follows: 11 - first pump source; 12 - second pump source; 21 - first focusing lens; 22 - second focusing lens; 3 - laser crystal; 31 - first end face; 32 - second end face; 4 - low-temperature electric refrigerator; 41 - cooling head; 5 - plane dichroic mirror; 6 - polarization beam splitter. DETAILED DESCRIPTION

[0033] The present invention will be further described below with reference to the accompanying drawings and exemplary embodiments.

[0034] Example 1

[0035] Reference Figure 1 A high-efficiency, compact, debugging-free mid-infrared 4μm band solid-state laser includes a first pump source 11, a low-temperature electric refrigerator 4, and a first focusing lens 21 and a laser crystal 3 arranged in sequence along the optical path of the first pump source 11.

[0036] The first pump source 11 is a fiber laser with a wavelength of 2.9 μm.

[0037] The first focusing lens 21 is a CaF2 lens with a focal length of 50 mm.

[0038] The laser crystal 3 is an iron-doped sulfide crystal; the iron ion doping concentration range is 50×10 18 cm -3 ; The base material of the laser crystal 3 is zinc selenide (ZnSe).

[0039] The low-temperature electric refrigerator 4 is a Stirling refrigerator. The temperature range of the cooling head 41 of the low-temperature electric refrigerator 4 is 40-100K. The cooling head 41 is set in a vacuum chamber. The laser crystal 3 is located in the vacuum chamber and is set on the cooling head 41 after being wrapped with a copper heat sink.

[0040] Two light-transmitting windows are provided at the intersection of the vacuum chamber and the optical path of the first pump source 11; the material of the two light-transmitting windows is calcium fluoride (CaF2), and both light-transmitting windows are coated with a dielectric film A, and the transmittance of the dielectric film A for the 2.5-5μm band laser is ≥95%.

[0041] The laser crystal 3 is provided with a first end face 31 and a second end face 32 at the intersection of the optical path of the first pump source 11. The first end face 31 and the second end face 32 are respectively coated with a fully reflective dielectric film B and an output dielectric film C; the fully reflective dielectric film B has a transmittance of ≥95% for the pump light of the first pump source 11 and a reflectance of ≥98% for 4μm band laser; the output dielectric film C has a transmittance of ≥95% for the pump light of the first pump source 11 and a reflectance of 70% for 4μm band laser; the 4μm band laser has a wavelength of 3.8 to 5μm.

[0042] This embodiment uses forward pumping. Pump light from the first pump source 11 is incident on the first end face 31 to generate 4μm laser light, which is then emitted from the second end face 32. Increasing the pump power of the first pump source 11 increases the output power of the 4μm laser light.

[0043] Example 2

[0044] Reference Figure 2 A high-efficiency, compact, debugging-free mid-infrared 4μm band solid-state laser includes a first pump source 11, a low-temperature electric refrigerator 4, and a first focusing lens 21 and a laser crystal 3 arranged in sequence along the optical path of the first pump source 11.

[0045] This embodiment adopts a backward pumping method. A plane dichroic mirror 5 is provided between the first pump source 11 and the first focusing lens 21. The included angle between the plane dichroic mirror 5 and the pump light of the first pump source 11 is 45°. The plane dichroic mirror 5 has a transmittance of ≥95% for the pump light of the first pump source 11 and a reflectivity of ≥99% for 4μm band laser. The pump light of the first pump source 11 is incident on the second end face 32 to generate 4μm band laser light. The 4μm band laser light is emitted from the second end face 32, focused by the first focusing lens 21, and reflected by the plane dichroic mirror 5 before being output. As the pump power increases, the power of the 4μm band laser light increases accordingly.

[0046] In this embodiment, the first pump source 11 is a fiber laser with a wavelength of 2.5 μm. The reflectivity of the output dielectric film C for 4 μm laser is 90%. The focal length of the first focusing lens 21 is 25 mm. The iron ion doping concentration of the laser crystal 3 is 45×10 18 cm -3 The base material of the laser crystal 3 is zinc sulfide (ZnS), and the material of the two light windows is magnesium fluoride (MgF2).

[0047] The rest of the configuration of this embodiment is the same as that of the first embodiment.

[0048] Example 3

[0049] A high-efficiency, compact, debugging-free mid-infrared 4μm band solid-state laser comprises a first pump source 11, a low-temperature electric refrigerator 4, and a first focusing lens 21 and a laser crystal 3 sequentially arranged along the optical path of the first pump source 11.

[0050] Reference Figure 3 This embodiment further includes a second pump source 12 and a second focusing lens 22 .

[0051] This embodiment adopts a bidirectional pumping method. A plane dichroic mirror 5 is arranged between the first pump source 11 and the first focusing lens 21. The angle between the plane dichroic mirror 5 and the pump light of the first pump source 11 is 45°. The plane dichroic mirror 5 has a transmittance of ≥95% for the pump light of the first pump source 11 and a reflectivity of ≥99% for 4μm band laser. After the pump light of the first pump source 11 is incident on the second end face 32, 4μm band laser light is generated, and the 4μm band laser light is emitted from the second end face 32.

[0052] The second pump source 12 is arranged opposite to the first pump source 11 and their optical paths overlap. A first focusing lens 21 is arranged between the second pump source 12 and the laser crystal 3. The pump light of the second pump source 12 is incident from the first end face 31 to generate 4μm band laser light. The 4μm band laser light is emitted from the second end face 32, and then focused by the first focusing lens 21 and reflected by the plane dichroic mirror 5 before being output.

[0053] In this embodiment, the first pump source 11 is a fiber laser with a wavelength of 3.4 μm. The reflectivity of the output dielectric film C for 4 μm laser is 10%. The first focusing lens 21 and the second focusing lens 22 are both CaF2 lenses with a focal length of 200 mm. The iron ion doping concentration of the laser crystal 3 is in the range of 0.5×10 18 cm -3 The base material of the laser crystal 3 is zinc telluride (ZnTe). The material of the two light-transmitting windows is zinc selenide (ZnSe). The transmittance of the fully reflective dielectric film B and the output dielectric film C to the pump light of the second pump source 12 is ≥95%.

[0054] In other embodiments, the focal length of the second focusing lens 22 is within a range of 25 to 200 mm.

[0055] The rest of the configuration of this embodiment is the same as that of the first embodiment.

[0056] Example 4

[0057] Reference Figure 4 A high-efficiency, compact, debugging-free mid-infrared 4μm band solid-state laser includes a first pump source 11, a second pump source 12, a polarization beam splitter 6, a low-temperature electric refrigerator 4, a first focusing lens 21, and a laser crystal 3.

[0058] The first pump source 11 and the second pump source 12 are fiber lasers with a wavelength of 2.9 μm.

[0059] The first focusing lens 21 is a CaF2 lens with a focal length of 50 mm.

[0060] The laser crystal 3 is an iron-doped sulfide crystal; the iron ion doping concentration range is 50×10 18 cm -3 ; The base material of the laser crystal 3 is zinc selenide (ZnSe).

[0061] The low-temperature electric refrigerator 4 is a Stirling refrigerator. The temperature range of the cooling head 41 of the low-temperature electric refrigerator 4 is 40-100K. The cooling head 41 is set in a vacuum chamber. The laser crystal 3 is located in the vacuum chamber and is set on the cooling head 41 after being wrapped with a copper heat sink.

[0062] The optical path of the second pump source 12 is perpendicular to the optical path of the first pump source 11, the first pump source 11 is P-polarized, and the second pump source 12 is S-polarized; the polarization beam splitter 6 is arranged at the intersection of the optical paths of the first pump source 11 and the second pump source 12, and is used to combine the pumping light of the first pump source 11 and the pumping light of the second pump source 12 to form a combined light; the first focusing lens 21 and the laser crystal 3 are arranged in sequence along the optical path of the combined light.

[0063] Two light-transmitting windows are provided at the intersection of the vacuum chamber and the optical path of the first pump source 11; the material of the two light-transmitting windows is calcium fluoride (CaF2), and both light-transmitting windows are coated with a dielectric film A, and the transmittance of the dielectric film A for the 2.5-5μm band laser is ≥95%.

[0064] The laser crystal 3 is provided with a first end face 31 and a second end face 32 at the intersection of the optical path of the first pump source 11. The first end face 31 and the second end face 32 are respectively coated with a fully reflective dielectric film B and an output dielectric film C; the fully reflective dielectric film B has a transmittance of ≥95% for the pump light of the first pump source 11 and a reflectance of ≥98% for 4μm band laser; the output dielectric film C has a transmittance of ≥95% for the pump light of the first pump source 11 and a reflectance of 70% for 4μm band laser; the 4μm band laser has a wavelength of 3.8 to 5μm.

[0065] This embodiment adopts a polarization combining forward pumping mode. The combined light is incident from the first end face 31 to generate 4 μm band laser light, which is then emitted from the second end face 32 .

[0066] Compared with the first embodiment, this embodiment increases the unidirectional pump power and improves the laser output level.

[0067] Example 5

[0068] Reference Figure 4 In this embodiment, the first pump source 11 and the second pump source 12 are fiber lasers with a wavelength of 2.5 μm. The reflectivity of the output dielectric film C for 4 μm lasers is 10%. The focal length of the first focusing lens 21 is 200 mm. The iron ion doping concentration of the laser crystal 3 is in the range of 0.5×10 18 cm -3 The base material of the laser crystal 3 is cadmium selenide (CdSe). The material of the two light-transmitting windows is magnesium fluoride (MgF2). Both light-transmitting windows are coated with a dielectric film A. The dielectric film A has a transmittance of ≥95% for lasers in the 2.5-5 μm wavelength range.

[0069] The rest of the configuration of this embodiment is the same as that of the fourth embodiment.

[0070] Example 6

[0071] Reference Figure 4 In this embodiment, the first pump source 11 and the second pump source 12 are fiber lasers with a wavelength of 3.4 μm. The reflectivity of the output dielectric film C for 4 μm laser is 10%. The focal length range of the first focusing lens 21 is 25 mm. The iron ion doping concentration of the laser crystal 3 is in the range of 20×10 18 cm -3 The base material of the laser crystal 3 is zinc telluride (ZnTe). The material of the two light-transmitting windows is zinc selenide (ZnSe). Both light-transmitting windows are coated with a dielectric film A. The dielectric film A has a transmittance of ≥95% for lasers in the 2.5-5 μm wavelength range.

[0072] The rest of the configuration of this embodiment is the same as that of the fourth embodiment.

[0073] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them. For ordinary professional and technical personnel in this field, the specific technical solutions recorded in the above embodiments can be modified, or some of the technical features therein can be replaced by equivalents. These modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions protected by the present invention.

Claims

1. A high-efficiency, compact, debug-free mid-infrared 4μm band solid-state laser, characterized by: It comprises a first pump source (11), a low-temperature electric refrigerator (4), and a first focusing lens (21) and a laser crystal (3) arranged in sequence along the optical path of the first pump source (11); The laser crystal (3) is an iron-doped sulfide crystal, wherein the iron ion doping concentration range is 0.5×10 18 cm -3 ~50×10 18 cm -3 The base material of the laser crystal (3) is one of zinc selenide, zinc sulfide, zinc telluride and cadmium selenide; The temperature range of the cooling head (41) of the low-temperature electric refrigerator (4) is 40-100K, the cooling head (41) is arranged in a vacuum chamber, and the laser crystal (3) is located in the vacuum chamber and is arranged on the cooling head (41) after being wrapped with a copper heat sink; two light-transmitting windows are provided at the intersection of the vacuum chamber and the optical path of the first pump source (11); the laser crystal (3) is provided with a first end face (31) and a second end face (32) at the intersection of the optical path of the first pump source (11), and the first end face (31) and the second end face (32) are respectively plated with a fully reflective dielectric film B and an output dielectric film C; the fully reflective dielectric film B has a transmittance of ≥95% for the pump light of the first pump source (11) and a reflectance of ≥98% for the 4μm band laser; the output dielectric film C has a transmittance of ≥95% for the pump light of the first pump source (11) and a reflectance of 10-90% for the 4μm band laser; The pump light of the first pump source (11) is focused by the first focusing lens (21) and incident on the first end face (31) or the second end face (32) of the laser crystal (3) to generate 4 μm-band laser light, which is then emitted from the second end face (32); The 4 μm band laser is a laser with a wavelength of 3.8 to 5 μm.

2. The high-efficiency, compact, debugging-free mid-infrared 4μm band solid-state laser according to claim 1, characterized in that: The first pump source (11) is a laser with a wavelength in the range of 2.5 to 3.4 μm.

3. The high-efficiency, compact, debug-free mid-infrared 4μm band solid-state laser according to claim 2, characterized in that: The material of the two light-transmitting windows is one of calcium fluoride, magnesium fluoride and zinc selenide. Both light-transmitting windows are plated with a dielectric film A, and the dielectric film A has a transmittance of ≥95% for 2.5-5 μm band laser.

4. The high-efficiency, compact, debugging-free mid-infrared 4μm band solid-state laser according to claim 3, characterized in that: The first focusing lens (21) is a CaF2 lens with a focal length ranging from 25 to 200 mm.

5. A high-efficiency, compact, debug-free mid-infrared 4μm band solid-state laser according to any one of claims 1 to 4, characterized in that: A plane dichroic mirror (5) is provided between the first pump source (11) and the first focusing lens (21); the angle between the plane dichroic mirror (5) and the pump light of the first pump source (11) is 45°; the plane dichroic mirror (5) has a transmittance of ≥95% for the pump light of the first pump source (11) and a reflectance of ≥99% for 4μm band laser light; the pump light of the first pump source (11) passes through the plane dichroic mirror (5) and is incident on the second end face (32) of the laser crystal (3), thereby generating 4μm band laser light; the 4μm band laser light is emitted from the second end face (32), is focused by the first focusing lens (21), and is reflected by the plane dichroic mirror (5) before being output.

6. The high-efficiency, compact, debugging-free mid-infrared 4μm band solid-state laser according to claim 5, characterized in that: The laser diode further comprises a second pumping source (12) and a second focusing lens (22). The second pumping source (12) and the first pumping source (11) are arranged opposite to each other and their optical paths overlap. The second focusing lens (22) is arranged between the second pumping source (12) and the laser crystal (3). Pumping light from the second pumping source (12) is incident on the first end face (31) to generate 4μm-band laser light, which is then emitted from the second end face (32). The transmittance of the fully reflective dielectric film B and the output dielectric film C to the pump light of the second pump source (12) is ≥95%; The second focusing lens (22) is a CaF2 lens with a focal length ranging from 25 to 200 mm.

7. A high-efficiency, compact, debug-free mid-infrared 4μm band solid-state laser, characterized by: It comprises a first pump source (11), a second pump source (12), a polarization beam splitter (6), a low-temperature electric refrigerator (4), a first focusing lens (21), and a laser crystal (3); The temperature range of the cooling head (41) of the low-temperature electric refrigerator (4) is 40-100K, the cooling head (41) is arranged in a vacuum chamber, and the laser crystal (3) is located in the vacuum chamber and is arranged on the cooling head (41) after being wrapped with a copper heat sink; The first pump source (11) and the second pump source (12) are lasers with wavelengths in the range of 2.5 to 3.4 μm; the laser crystal (3) is an iron-doped sulfide crystal, wherein the iron ion doping concentration ranges from 0.5×10 18 cm -3 ~50×10 18 cm -3 The base material of the laser crystal (3) is one of zinc selenide, zinc sulfide, zinc telluride and cadmium selenide; The optical path of the second pump source (12) is perpendicular to the optical path of the first pump source (11); the first pump source (11) is P-polarized, and the second pump source (12) is S-polarized; the polarization beam splitter (6) is arranged at the intersection of the optical paths of the first pump source (11) and the second pump source (12), and is used to combine the pump light of the first pump source (11) and the second pump source (12) to form a combined light beam; the first focusing lens (21) and the laser crystal (3) are arranged in sequence along the optical path of the combined light beam; Two light-transmitting windows are provided at the intersection of the vacuum chamber and the combined light path; a first end face (31) and a second end face (32) are provided at the intersection of the laser crystal (3) and the combined light path, respectively; the first end face (31) and the second end face (32) are respectively plated with a fully reflective dielectric film B and an output dielectric film C; the fully reflective dielectric film B has a transmittance of ≥95% for the combined light and a reflectance of ≥98% for 4μm-band lasers; the output dielectric film C has a transmittance of ≥95% for the combined light and a reflectance of 10-90% for 4μm-band lasers; The combined light is focused by a first focusing lens (21), incident on a first end face (31) of a laser crystal (3) to generate 4 μm-band laser light, which is then emitted from a second end face (32); The 4 μm band laser is a laser with a wavelength of 3.8 to 5 μm.

8. The high-efficiency, compact, debugging-free mid-infrared 4μm band solid-state laser according to claim 7, characterized in that: The material of the two light-transmitting windows is one of calcium fluoride, magnesium fluoride and zinc selenide. Both light-transmitting windows are coated with a dielectric film A. The dielectric film A has a transmittance of ≥95% for lasers in the 2.5-5 μm band. The first focusing lens (21) is a CaF2 lens with a focal length range of 25-200 mm.

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