A high power quantum cascade laser beam combining device and method

Abstract

The application provides a high-power quantum cascade laser beam combining device and method, which comprises at least a first spatial beam combining unit and a second spatial beam combining unit arranged perpendicularly to each other, wherein the first spatial beam combining unit and the second spatial beam combining unit are identical in structure, and each of the first spatial beam combining unit and the second spatial beam combining unit comprises a base, eight single-tube quantum cascade lasers, eight reflecting turning prisms, a first-stage beam-reducing single convex lens, a second-stage beam-reducing double convex lens and a double concave lens. The application can solve the problems of the limited output power of the existing single-tube quantum cascade laser, the too large spatial beam combining spot "dead zone" and the insufficient polarization beam combining purity, and through the good combination of spatial beam combining and polarization beam combining, the spatial filling factor and the polarization beam combining purity are improved, and the high-power, high-beam-quality mid-infrared laser output is realized.

Description

Technical Field

[0001] This invention relates to the field of semiconductor laser technology, and in particular to a high-power quantum cascade laser beam combining device and method. Background Technology

[0002] Quantum cascade lasers (QCLs) are monopolar semiconductor lasers based on interband electron transitions, with emission wavelengths primarily covering the mid-infrared to terahertz band. Due to their promising applications in infrared countermeasures, trace gas detection, and medical diagnostics, they have received widespread attention in recent years.

[0003] However, the output power of a single-tube quantum cascade laser (QCL) is typically limited (a few watts to tens of watts), making it difficult to meet the demands of high-power applications. To improve laser output power, beam combining techniques are commonly used to spatially combine, polarize combine, or wavelength combine the output beams of multiple QCLs. Existing beam combining schemes mostly employ spatial arrangement with lens collimation, but these suffer from the following problems: beam quality degradation, with simple parallel coupling leading to a significant decrease in beam quality after combining; low beam combining efficiency, as conventional spatial beam combining does not fully utilize polarization characteristics and involves numerous optical components and complex structures; difficult thermal management, with heat dissipation becoming a bottleneck when multiple lasers are densely arranged; and high coupling loss, with the mismatch between the beam shape and fiber core diameter after combining causing significant coupling loss. Furthermore, conventional schemes do not consider elliptical spot direction optimization, resulting in low space utilization. Therefore, developing a high-power quantum cascade laser beam combining structure that is compact, has high beam combining efficiency, good beam quality, and facilitates fiber coupling output is a pressing technical problem to be solved in this field. Summary of the Invention

[0004] The primary objective of this invention is to provide a high-power quantum cascade laser beam combining device that can solve the problems of limited output power, excessively large "dead zone" of spatial beam combining spot, and insufficient polarization beam combining purity of existing single-tube quantum cascade lasers.

[0005] The second objective of this invention is to provide a method for combining high-power quantum cascade laser beams.

[0006] This invention provides a high-power quantum cascade laser beam combining device, comprising at least a first spatial beam combining unit and a second spatial beam combining unit arranged perpendicularly to each other, wherein the first spatial beam combining unit and the second spatial beam combining unit have the same structure; Wherein, each of the first spatial beam combining unit and the second spatial beam combining unit comprises a base, eight single-tube quantum cascade lasers, eight reflecting turning prisms, a first-stage beam-reducing single convex lens, a second-stage beam-reducing double convex lens, and a biconcave lens; the eight single-tube quantum cascade lasers are uniformly fixed on the base in a circular array, an aspherical collimating mirror is installed at the light outlet of each single-tube quantum cascade laser, and the eight single-tube quantum cascade lasers respectively emit eight beams of laser with elliptical spots; each of the reflecting turning prisms is correspondingly disposed on the light-emitting optical path of each single-tube quantum cascade laser, and the reflecting turning prism is configured to change the propagation direction of the laser beam three times, so that the major axis direction of each elliptical spot faces the center of the circular array; the first-stage beam-reducing single convex lens is configured to perform primary convergence on the eight laser beams turned by the respective reflecting turning prisms to reduce the spot size and the beam spacing; the second-stage beam-reducing double convex lens is configured to further converge the eight laser beams that have passed through the first-stage beam-reducing single convex lens, so that the spot centers of the eight laser beams converge and coincide at one point at the back focal point of the second-stage beam-reducing double convex lens; the biconcave lens is configured to diverge the beam that has undergone two stages of beam reduction and convergence and convert it into a parallel beam for emission.

[0007] Specifically, the reflecting turning prism is provided with a first reflecting surface, a second reflecting surface and a third reflecting surface, and the laser beam sequentially passes through the first reflecting surface, the second reflecting surface and the third reflecting surface to undergo three times of reflection and turning before exiting.

[0008] Specifically, the exit positions of the eight laser beams of the first spatial beam combining unit after being turned by the corresponding reflecting turning prisms are uniformly distributed in a circular shape, and all the exit beams are parallel to the optical axis of the first spatial beam combining unit; The exit positions of the eight laser beams of the second spatial beam combining unit after being turned by the corresponding reflecting turning prisms are uniformly distributed in a circular shape, and all the exit beams are parallel to the optical axis of the second spatial beam combining unit.

[0009] Specifically, the first reflecting surface, the second reflecting surface and the third reflecting surface are all coated with a mid-infrared band high-reflection film, with a reflectivity greater than 95%; each light-passing surface of the reflecting turning prism is coated with an anti-reflection film, with a transmittance greater than 95%.

[0010] Specifically, the focal length of the first-stage beam-reducing single convex lens is f1, the focal length of the second-stage beam-reducing double convex lens is f2, and f2<f1; the focal length of the biconcave lens is f3, f3 is a negative value, and the focal position of the biconcave lens is set such that the beam that has undergone two stages of convergence becomes parallel light after passing through the biconcave lens.

[0011] Specifically, it also includes a first half-wave plate and a second half-wave plate, wherein the first half-wave plate is disposed in the outgoing light path of the first spatial beam combiner unit, and the second half-wave plate is disposed in the outgoing light path of the second spatial beam combiner unit; Both the first half-wave plate and the second half-wave plate are zero-order half-wave plates corresponding to the laser wavelength. Both the first half-wave plate and the second half-wave plate are coated with a mid-infrared anti-reflection film on their light-transmitting surfaces, with a transmittance >95%. The optical axis of the first half-wave plate is set to convert the incident light into pure P-light, and the optical axis of the second half-wave plate is set to convert the incident light into pure S-light. The purity of both P-light and S-light is >99%.

[0012] Specifically, it also includes a mid-infrared grating polarizer, wherein the infrared grating polarizer has a transmittance of >98% for P-light and a reflectance of >98% for S-light.

[0013] Specifically, it also includes a focusing lens group and an optical fiber. The incident end face of the focusing lens group and the incident end face of the optical fiber are coated with a mid-infrared anti-reflection film. The two laser beams with mutually perpendicular polarization directions emitted from the first spatial beam combining unit and the second spatial beam combining unit are polarized and combined by the mid-infrared grating polarizer, and then coupled into the optical fiber through the focusing lens group.

[0014] Specifically, the single-tube quantum cascade laser has an emission wavelength of 3~5μm, a continuous output power of ≥1W, and a polarization state of TM polarization with a polarization degree >95%.

[0015] The present invention also provides a method for beam combining high-power quantum cascade lasers, which employs the above-mentioned high-power quantum cascade laser beam combining device and specifically includes the following steps: The first spatial beam combiner and the second spatial beam combiner each emit eight elliptical laser beams through eight single-tube quantum cascade lasers. After being collimated by an aspherical collimating mirror, the propagation direction of the eight laser beams is transformed into the optical axis parallel to the optical axis of their respective spatial beam combining units by the corresponding reflective turning prisms, and the major axis of the eight elliptical laser spots is directed toward the center of the circular array formed by the eight single-tube quantum cascade lasers. After being redirected, the beams pass sequentially through a first-stage beam-shrinking single convex lens and a second-stage beam-shrinking double convex lens. The first-stage beam-shrinking single convex lens initially shrinks the eight laser beams, reducing the size of each beam spot and the center-to-center distance between adjacent beams. The second-stage beam-shrinking double convex lens further shrinks the eight laser beams, causing the centers of the eight laser beam spots after passing through the second-stage beam-shrinking double convex lens to converge and coincide at the rear focal point of the second-stage beam-shrinking double convex lens. The laser beam, after being converged by two stages, is incident on a biconcave lens and refracted by the biconcave lens before exiting as a parallel beam. The parallel beam emitted from the first spatial beam combiner unit is converted into pure P-beam by the first half-wave plate, and the parallel beam emitted from the second spatial beam combiner unit is converted into pure S-beam by the second half-wave plate. Two parallel beams of light with orthogonal polarization states are combined into one beam after passing through a mid-infrared grating polarizer; The combined beam of light is coupled into the optical fiber output through a focusing lens group.

[0016] The high-power quantum cascade laser beam combining device provided by this invention comprises a first spatial beam combining unit and a second spatial beam combining unit that are perpendicular to each other and have the same structure. Each spatial beam combining unit includes eight single-tube quantum cascade lasers arranged in a circular array. Each single-tube quantum cascade laser emits an elliptical laser beam, which is redirected by a reflection prism to change its propagation direction and make the major axis of the elliptical laser beam point towards the center of the circular array formed by the eight single-tube quantum cascade lasers, thereby significantly improving the space fill factor and reducing the beam parametric product after beam combining. Then, the beam is converged and reduced in two stages by a first-stage beam-shrinking single convex lens and a second-stage beam-shrinking double convex lens, achieving a stepwise compression of the beam spot size and beam spacing. After passing through the second-stage beam-shrinking double convex lens, the centers of the eight laser beams can converge and coincide at a single point at the back focal point of the second-stage beam-shrinking double convex lens, achieving spatial coincidence of each sub-beam at the focal point. Finally, the beam is diverged and collimated by a biconcave lens to obtain a single parallel combined beam, providing an ideal beam shape for subsequent polarization beam combining and fiber coupling.

[0017] Furthermore, by using two independent half-wave plates to convert the parallel beams emitted from the first and second spatial beam combining units into pure P-beams and pure S-beams respectively, stray light components are eliminated. The two parallel beams with orthogonal polarization states then pass through a mid-infrared grating polarizer, bringing the polarization beam combining efficiency close to the theoretical limit. Finally, they are coupled into the optical fiber through a focusing lens group, achieving high-power, high-beam-quality, and high beam combining efficiency mid-infrared laser output.

[0018] Therefore, the high-power quantum cascade laser beam combining device provided by the present invention combines spatial beam combining with polarization beam combining, improves the space fill factor and polarization beam combining purity, and realizes high-power, high-beam-quality, and high beam combining efficiency mid-infrared laser output, which can be widely used in directional infrared countermeasures, environmental monitoring and free-space optical communication and other fields. Attached Figure Description

[0019] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0020] Figure 1 This is an isometric side view of the high-power quantum cascade laser beam combining device of the present invention; Figure 2 This is a top view of the high-power quantum cascade laser beam combining device of the present invention; Figure 3 This is a three-dimensional structural diagram of the high-power quantum cascade laser beam combining device of the present invention; Figure 4 This is an axonometric view of the first direction of the reflecting steering prism in the high-power quantum cascade laser beam combining device of the present invention; Figure 5 This is an axonometric view of the second direction of the reflecting steering prism in the high-power quantum cascade laser beam combining device of the present invention; Figure 6 This is a diagram showing the beam arrangement of the eight laser beams emitted from the eight single-tube quantum cascade lasers in this invention after being redirected by corresponding reflecting prisms. Figure 7 This is a schematic diagram of the beams of the eight laser beams in this invention after passing through a first-stage beam-shrinking single convex lens, a second-stage beam-shrinking double convex lens, and a double concave lens.

[0021] Explanation of reference numerals in the attached figures: 1. Base; 2. Single-tube quantum cascade laser; 3. Aspherical collimating lens; 4. Reflecting steering prism; 5. First-stage beam-shrinking single convex lens; 6. Second-stage beam-shrinking biconvex lens; 7. Biconcave lens; 8a. First half-wave plate; 8b. Second half-wave plate; 9. Mid-infrared grating polarizer; 10. Focusing lens group; 11. Optical fiber. Detailed Implementation

[0022] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0024] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the stated features. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified. Furthermore, the terms "installed," "connected," and "linked" should be interpreted broadly; for example, they may refer to a fixed connection, a detachable connection, or an integral connection; they may refer to a mechanical connection or an electrical connection; they may refer to a direct connection or an indirect connection through an intermediate medium; and they may refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0025] like Figures 1 to 3 As shown, the high-power quantum cascade laser beam combining device of this invention includes a first spatial beam combining unit, a second spatial beam combining unit, a first half-wave plate 8a, a second half-wave plate 8b, a mid-infrared grating polarizer 9, a focusing lens group 10, and an optical fiber 11. The first and second spatial beam combining units have the same structure and are arranged perpendicularly. The first half-wave plate 8a is disposed in the output optical path of the first spatial beam combining unit, and the second half-wave plate 8b is disposed in the output optical path of the second spatial beam combining unit. Two laser beams with mutually perpendicular polarization directions are polarized and combined by the mid-infrared grating polarizer 9, and then coupled into the optical fiber 11 by the focusing lens group 10.

[0026] The following description uses the first spatial beam combining unit as an example. This first spatial beam combining unit includes a base 1, eight single-tube quantum cascade lasers 2, eight reflecting and steering prisms 4, a first-stage beam-shrinking single convex lens 5, a second-stage beam-shrinking biconvex lens 6, and a biconcave lens 7. The eight single-tube quantum cascade lasers 2 are uniformly fixed on the base 1 in a circular array, and each single-tube quantum cascade laser 2 has an aspherical collimating lens 3 mounted on its output port by adhesive bonding. The eight reflecting and steering prisms 4 are arranged radially, and each reflecting and steering prism 4 is correspondingly positioned in the output optical path of each single-tube quantum cascade laser 2. The single-tube quantum cascade laser 2 has an emission wavelength of 3~5μm, a continuous output power of ≥1W, and a polarization state of TM polarization with a polarization degree >95%.

[0027] like Figures 4 to 5As shown, each reflecting prism 4 is provided with a first reflecting surface 4-1, a second reflecting surface 4-2, and a third reflecting surface 4-3. The elliptical laser beam emitted from the single-tube quantum cascade laser 2 is collimated by the aspherical collimating lens 3 and then incident on the corresponding reflecting prism 4. After the laser beam is reflected three times by the first reflecting surface 4-1, the second reflecting surface 4-2, and the third reflecting surface 4-3, the propagation direction of the laser beam is changed so that the emitted beam is parallel to the optical axis of the first spatial beam combining unit, and the major axis of each elliptical laser beam is oriented towards the center of the circular array formed by the eight single-tube quantum cascade lasers 2.

[0028] Among them, the first reflective surface 4-1, the second reflective surface 4-2 and the third reflective surface 4-3 are all coated with a mid-infrared high-reflectivity film with a reflectivity greater than 95%, and the chamfer of each reflective surface is 45°; the other light-transmitting surfaces on the reflective steering prism 4 are all coated with an anti-reflection film with a transmittance greater than 95%.

[0029] The eight laser beams emitted from the eight single-tube quantum cascade lasers 2 are redirected by their corresponding reflecting and redirecting prisms 4, resulting in a uniformly distributed circular output position. All output beams are parallel to the optical axis of the first spatial beam combining unit, forming an approximately continuous annular energy distribution. The beam pattern after redirection is as follows: Figure 6 As shown.

[0030] Specifically, the first-stage beam-shrinking single convex lens 5 is set with the steering output surface of the eight reflecting steering prisms 4 to perform initial beam shrinking on the eight laser beams, so as to reduce the size of the single beam spot and the center distance between adjacent beams.

[0031] The second-stage beam-shrinking biconvex lens 6 is located in the output optical path of the first-stage beam-shrinking single convex lens 5, and the focal length of the second-stage beam-shrinking biconvex lens 6 is smaller than that of the first-stage beam-shrinking single convex lens 5. After passing through the second-stage beam-shrinking biconvex lens 6, the centers of the eight laser beams converge and coincide at the rear focal point of the second-stage beam-shrinking biconvex lens 6, achieving spatial overlap of each sub-beam at the focal point.

[0032] The front focal point of the biconcave lens 7 coincides spatially with the rear focal point of the second-order beam-contracting biconvex lens 6. After passing through the second-order beam-contracting biconvex lens 6, the diverging laser beam enters the biconcave lens 7 and exits as a parallel beam after refraction. At this point, the individual beams converge and are then collimated by the biconcave lens 7, forming a single parallel combined beam. The combined beam after passing through the biconcave lens 7 is as follows... Figure 7 As shown.

[0033] Specifically, both the first half-wave plate 8a and the second half-wave plate 8b are zero-order half-wave plates corresponding to the laser wavelength, with mid-infrared anti-reflection coatings on their light-transmitting surfaces, achieving a transmittance greater than 95%. The first half-wave plate 8a is positioned in the outgoing parallel optical path of the first spatial beam combiner unit, its optical axis adjusted to convert the incident linearly polarized light into P-light. The second half-wave plate 8b is positioned in the outgoing parallel optical path of the second spatial beam combiner unit, its optical axis adjusted to convert the incident light into S-light.

[0034] Specifically, the mid-infrared grating polarizer 9 has a transmittance of more than 98% for P-light and a reflectance of more than 98% for S-light. The P-light emitted from the first spatial beam combiner is transmitted, and the S-light emitted from the second spatial beam combiner is reflected. The two beams are then combined into one beam by the mid-infrared grating polarizer 9.

[0035] Specifically, the focusing lens group 10 is an aspherical focusing lens with an aperture larger than the size of the combined beam spot, and its incident end face is coated with a mid-infrared anti-reflection film. The optical fiber 11 is made of fluoride fiber, sulfide fiber, or telluride fiber, and the incident end face of the optical fiber 11 is coated with a mid-infrared anti-reflection film.

[0036] This invention also provides a method for combining high-power quantum cascade lasers, using the high-power quantum cascade laser combining device described above, specifically including the following steps: The first spatial beam combiner and the second spatial beam combiner each emit eight elliptical laser beams through eight single-tube quantum cascade lasers.

[0037] After being collimated by an aspherical collimating mirror, the propagation direction of the eight laser beams is transformed into the optical axis parallel to the optical axis of their respective spatial beam combining units by corresponding reflective turning prisms, and the major axis of the eight elliptical laser spots is directed toward the center of the circular array formed by the eight single-tube quantum cascade lasers.

[0038] After being redirected, the beams pass sequentially through a first-stage beam-shrinking single convex lens and a second-stage beam-shrinking double convex lens. The first-stage beam-shrinking single convex lens initially shrinks the eight laser beams, reducing the size of each beam spot and the center-to-center distance between adjacent beams. The second-stage beam-shrinking double convex lens further shrinks the eight laser beams, causing the centers of the eight laser beam spots after passing through the second-stage beam-shrinking double convex lens to converge and coincide at the rear focal point of the second-stage beam-shrinking double convex lens.

[0039] The laser beam, after being converged by two stages, is incident on a biconcave lens and refracted by the biconcave lens before exiting as a parallel beam.

[0040] The parallel beam emitted from the first spatial beam combiner unit is converted into pure P-beam by the first half-wave plate, and the parallel beam emitted from the second spatial beam combiner unit is converted into pure S-beam by the second half-wave plate.

[0041] Two parallel beams of light with orthogonal polarization states are combined into one beam after passing through a mid-infrared grating polarizer.

[0042] The combined beam of light is coupled into the optical fiber output through a focusing lens group.

[0043] In summary, the high-power quantum cascade laser beam combining device and method of the present invention has the following significant advantages compared with the existing beam combining scheme that uses linear laser arrays and single-stage beam shrinking: In existing technologies, multiple single-tube quantum cascade lasers are arranged in a straight line or in a stepped manner. The major axis of each elliptical spot is not optimized, and there are large gaps between the spots. After single-stage beam shrinking, the gap between the spots is only compressed to a limited extent, and there are still obvious gap regions between the spots, i.e., there are large "dead zones". After beam combining, the overall spot is irregularly multi-lobed or elongated, with a low fill factor, poor beam quality, and difficulty in effectively coupling into the optical fiber.

[0044] In this embodiment, eight single-tube quantum cascade lasers are arranged in a circular array. After three reflections and redirections, the major axis of each elliptical laser spot is aligned with the center of the circular array formed by the eight single-tube quantum cascade lasers, creating a continuous energy distribution on the circumference. More importantly, after passing through a second-stage beam-shrinking biconvex lens, the centers of the eight laser beams converge at a single focal point, achieving complete spatial overlap between the sub-beams. There are no gaps between the beams, and the "dead zone" is completely eliminated, resulting in a nearly circular beam after beam combining, rather than the multi-lobed or elongated beams commonly found in existing solutions. Therefore, the combined effect of these technologies significantly improves the beam quality of the combined beam compared to existing solutions, effectively solving the beam quality degradation problem caused by gaps and "dead zones" in existing beam combining schemes. This provides a reliable technical guarantee for the efficient fiber-coupled output of high-power mid-infrared lasers.

[0045] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A high-power quantum cascade laser beam combining device, characterized in that, at least comprising a first spatial beam combining unit and a second spatial beam combining unit arranged perpendicularly to each other, where the first spatial beam combining unit and the second spatial beam combining unit have the same structure; wherein, each of the first spatial beam combining unit and the second spatial beam combining unit comprises a base, eight single-tube quantum cascade lasers, eight reflecting turning prisms, a first-stage beam-shrinking plano-convex lens, a second-stage beam-shrinking biconvex lens, and a biconcave lens; the eight single-tube quantum cascade lasers are uniformly fixed on the base in a circular array, an aspherical collimating mirror is installed at the light outlet of each single-tube quantum cascade laser, and the eight single-tube quantum cascade lasers respectively emit eight beams of laser with elliptical spots; each of the reflecting turning prisms is correspondingly disposed on the light output optical path of each single-tube quantum cascade laser, and the reflecting turning prism is configured to change the propagation direction of the laser beam three times, and make the long axis direction of each elliptical spot face the center of the circular array; the first-stage beam-shrinking plano-convex lens is configured to perform initial convergence on the eight laser beams turned by the respective reflecting turning prisms to reduce the spot size and the beam spacing; the second-stage beam-shrinking biconvex lens is configured to further converge the eight laser beams that have passed through the first-stage beam-shrinking plano-convex lens, so that the spot centers of the eight laser beams converge and coincide at one point at the rear focal point of the second-stage beam-shrinking biconvex lens; the biconcave lens is configured to diverge the beam that has undergone two-stage beam-shrinking convergence and convert it into a parallel beam for emission.

2. The high-power quantum cascade laser beam combiner according to claim 1, characterized in that, The reflecting turning prism is provided with a first reflecting surface, a second reflecting surface and a third reflecting surface, and the laser beam sequentially passes through the first reflecting surface, the second reflecting surface and the third reflecting surface to undergo three reflections and turning before exiting.

3. The high-power quantum cascade laser beam combiner according to claim 2, characterized in that, The exit positions of the eight laser beams of the first spatial beam combining unit after being turned by the corresponding reflecting turning prisms are uniformly distributed in a circular shape, and all exit beams are parallel to the optical axis of the first spatial beam combining unit; The exit positions of the eight laser beams of the second spatial beam combining unit after being turned by the corresponding reflecting turning prisms are uniformly distributed in a circular shape, and all exit beams are parallel to the optical axis of the second spatial beam combining unit.

4. The high-power quantum cascade laser beam combiner according to claim 2, characterized in that, Each of the first reflecting surface, the second reflecting surface and the third reflecting surface is coated with a mid-infrared band high-reflection film with a reflectance greater than 95%; each light-passing surface of the reflecting turning prism is coated with an anti-reflection film with a transmittance greater than 95%.

5. The high-power quantum cascade laser beam combiner according to claim 1, characterized in that, The focal length of the first-stage beam-shrinking plano-convex lens is f1, the focal length of the second-stage beam-shrinking biconvex lens is f2, and f2<f1; the focal length of the biconcave lens is f3, f3 is a negative value, and the focal position of the biconcave lens is set such that the beam that has undergone two-stage convergence becomes parallel light after passing through the biconcave lens.

6. The high-power quantum cascade laser beam combiner according to claim 1, characterized in that, Further comprising a first half-wave plate and a second half-wave plate, wherein the first half-wave plate is disposed on the exit optical path of the first spatial beam combining unit, and the second half-wave plate is disposed on the exit optical path of the second spatial beam combining unit; Both the first half-wave plate and the second half-wave plate are zero-order half-wave plates corresponding to the laser wavelength. Both the first half-wave plate and the second half-wave plate are coated with a mid-infrared anti-reflection film on their light-transmitting surfaces, with a transmittance >95%. The optical axis of the first half-wave plate is set to convert the incident light into pure P-light, and the optical axis of the second half-wave plate is set to convert the incident light into pure S-light. The purity of both P-light and S-light is >99%.

7. The high-power quantum cascade laser beam combiner according to claim 6, characterized in that, It also includes a mid-infrared grating polarizer, wherein the infrared grating polarizer has a transmittance of >98% for P-light and a reflectance of >98% for S-light.

8. The high-power quantum cascade laser beam combiner according to claim 7, characterized in that, It also includes a focusing lens group and an optical fiber. The incident end face of the focusing lens group and the incident end face of the optical fiber are coated with a mid-infrared anti-reflection film. The two laser beams with mutually perpendicular polarization directions emitted from the first spatial beam combining unit and the second spatial beam combining unit are polarized and combined by the mid-infrared grating polarizer, and then coupled into the optical fiber through the focusing lens group.

9. The high-power quantum cascade laser beam combiner according to claim 1, characterized in that, The single-tube quantum cascade laser has an emission wavelength of 3~5μm, a continuous output power of ≥1W, and a polarization state of TM polarization with a polarization degree of >95%.

10. A method for beam combining high-power quantum cascade lasers, characterized in that, The high-power quantum cascade laser beam combiner as described in any one of claims 1 to 9 comprises the following steps: The first spatial beam combiner and the second spatial beam combiner each emit eight elliptical laser beams through eight single-tube quantum cascade lasers. After being collimated by an aspherical collimating mirror, the propagation direction of the eight laser beams is transformed into the optical axis parallel to the optical axis of their respective spatial beam combining units by the corresponding reflective turning prisms, and the major axis of the eight elliptical laser spots is directed toward the center of the circular array formed by the eight single-tube quantum cascade lasers. After being redirected, the beams pass sequentially through a first-stage beam-shrinking single convex lens and a second-stage beam-shrinking double convex lens. The first-stage beam-shrinking single convex lens initially shrinks the eight laser beams, reducing the size of each beam spot and the center-to-center distance between adjacent beams. The second-stage beam-shrinking double convex lens further shrinks the eight laser beams, causing the centers of the eight laser beam spots after passing through the second-stage beam-shrinking double convex lens to converge and coincide at the rear focal point of the second-stage beam-shrinking double convex lens. The laser beam, after being converged by two stages, is incident on a biconcave lens and refracted by the biconcave lens before exiting as a parallel beam. The parallel beam emitted from the first spatial beam combiner unit is converted into pure P-beam by the first half-wave plate, and the parallel beam emitted from the second spatial beam combiner unit is converted into pure S-beam by the second half-wave plate. Two parallel beams of light with orthogonal polarization states are combined into one beam after passing through a mid-infrared grating polarizer; The combined beam of light is coupled into the optical fiber output through a focusing lens group.

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