A high-power mid-infrared laser generating device and generating method for multiple transverse modes

Abstract

A high-power mid-infrared laser generating device and generating method with multiple transverse modes, wherein a first plano-convex mirror collimates and focuses the laser generated by a pump source onto a second plano-convex mirror; the second plano-convex mirror collimates and focuses the light beam focused by the first plano-convex mirror onto a cone lens, and the annular light beam generated by the cone lens is focused onto a laser resonant cavity composed of an input coupling mirror and an output coupling mirror after passing through a third plano-convex mirror, and the laser passing through a laser gain medium generates a particle number inversion, and part of the laser is output through an output coupling mirror to obtain a high-power mid-infrared laser; the laser gain medium is fixed to a one-dimensional precision electric displacement stage A, and the one-dimensional precision electric displacement stage A can move along the laser propagation axis. The present invention can automatically switch and realize the output of multiple high-order transverse mode light beams such as high-power annular vortex light beams, flat-top Gaussian light beams, and fundamental mode Gaussian light beams, solving the problems of the current single laser output mode, low output laser power, and poor phase control capability.

Description

Technical Field

[0001] The invention relates to a mid-infrared laser generating device, in particular to a high-power mid-infrared laser generating device with multiple transverse modes and a generating method, belonging to the technical field of high-power mid-infrared lasers. Background Art

[0002] Fundamental transverse mode lasers are most widely used in laser processing due to their high brightness and good directionality. However, higher-order mode lasers have recently attracted widespread attention from academia and industry due to their greater information content and degrees of freedom. As a typical higher-order mode, vortex beams are distributed in a ring shape in space and have orbital angular momentum characteristics. They can be used to transfer angular momentum between microscopic particles or atoms. In recent years, they have shown very attractive application prospects in multi-trap optical tweezers, micro-nano processing, and high-efficiency, high-precision laser processing. The doctoral thesis "Research on the Intracavity Generation Technology and Application of Vortex Beams" of Shanghai Jiaotong University mentioned that scientists have expanded the manipulation of vortex light to three-dimensional space and realized three-dimensional manipulation of micro-nano particles; vortex beams can also be used in super-resolution microscopic imaging, optical vortex communication, quantum communication, etc. The master's thesis "Generation and Application of Ideal Flat-Top Beams" of the University of Electronic Science and Technology of China mentioned that flat-top beams have a wide range of applications in laser material processing and interaction research, fiber injection systems, optical data and image processing, lithography, laser material thermal processing, micromanipulation, optical biomedicine and military fields.

[0003] On August 4, 2010, a Chinese invention patent disclosed an "adaptive high-order transverse mode laser coherent synthesis device" with a publication number of CN101794962A. The high-order transverse mode laser output by a solid laser is incident on a deformable mirror after being expanded by a beam matching system. The beam reflected by the deformable mirror then passes through a beam splitter, an attenuation system, and a focusing lens in sequence, and converges on a CCD camera at the focal position. By driving the deformable mirror to produce corresponding deformation, the distortion in the overall wavefront phase of the high-order transverse mode laser is compensated, the phase jump of the side lobes on both sides of each node line of the high-order transverse mode laser is compensated, and the coherence characteristics and focusability of the high-order transverse mode laser are improved; on March 2, 2016, a Chinese invention patent disclosed an "adaptive high-order transverse mode laser coherent synthesis device" with a publication number of CN101794962A. 05375250A's "A method and device for generating high-order transverse modes by atom-cavity coupling" states that in a system coupled by an atomic vapor chamber and a standing wave cavity, when a pair of strong coherent coupling fields radiate through the atomic medium in the cavity, the medium in the cavity modulates the refractive index of the weak cavity mode field, thereby inducing the generation of high-order transverse modes.

[0004] Due to the complexity and inherent instability of high-order modes, the generation and regulation of pure high-order modes has become a problem. The existing methods such as perforated mirrors, hollow optical fibers, and conical refractive ring mirrors have solved the problem of generating a single high-order mode. However, due to the complex devices and systems used, it is difficult to effectively achieve the simultaneous generation and switching of multiple high-order transverse modes, especially in the field of 2um mid-infrared lasers. The quantum efficiency of lasers in this band is low, and the waste heat of high-power laser systems is very serious, which further increases the complexity of high-order mode regulation. After reviewing the research on high-order mode instability by researchers over the past 10 years, it is found that there is still room for further improvement in theory, and high-power laser technology based on high-order transverse modes needs to be improved.

[0005] Focusing on the field of laser processing, there are still a series of problems with laser light sources: first, the laser mode is single, and a single mode with Gaussian distribution is generally pursued, which limits the increase in power. Gaussian mode is not conducive to laser processing, and flat-top beam processing is better in industry; secondly, methods that can generate high-order modes, such as spatial light modulators (SLM), have low damage thresholds and cannot generate high power, especially in the mid-infrared band. SLM devices are immature and the mode control method is complex; finally, most of the ring light and flat-top light generated by existing methods are incoherent light. The extra-cavity shaping method used by IPG Photonics uses frosted glass or capillaries, and has poor phase control capabilities. Summary of the invention

[0006] The purpose of the present invention is to provide a high-power mid-infrared laser generating device and a generating method with multiple transverse modes, which can automatically switch and realize the output of multiple high-order transverse mode beams such as high-power annular vortex beams, flat-top Gaussian beams, and fundamental mode Gaussian beams, so as to solve the problems of the current single laser output mode, low output laser power, and poor phase control capability.

[0007] In order to achieve the above-mentioned object, the present invention provides a high-power mid-infrared laser generating device with multiple transverse modes, including a pump source for providing horizontal laser, and also including a first plano-convex mirror, a second plano-convex mirror, an aconic lens, a third plano-convex mirror, an input coupling mirror, a laser gain medium, and an output coupling mirror coaxially arranged along the laser direction;

[0008] The first plano-convex mirror is used to collimate and focus the laser generated by the pump source onto the second plano-convex mirror;

[0009] The second plano-convex mirror is used to collimate and focus the light beam focused by the first plano-convex mirror onto the aconic lens. The Bessel annular light beam generated by the aconic lens is focused into the laser resonant cavity composed of the input coupling mirror and the output coupling mirror after passing through the third plano-convex mirror. The laser passing through the gain medium generates a population inversion and oscillates back and forth between the input coupling mirror and the output coupling mirror. Part of the laser is output through the output coupling mirror to obtain a high-power mid-infrared laser.

[0010] The laser gain medium is fixed to a one-dimensional precision electric translation stage A, and the one-dimensional precision electric translation stage A can move along the laser propagation axis, wherein the movement speed and direction of the one-dimensional precision electric translation stage A can be controlled by computer software programming;

[0011] Preferably, the pump source of the present invention is a fiber laser with 1940nm single-mode fiber output or a semiconductor laser coupled to a single-mode fiber, the output wavelength matches the absorption wavelength of the laser gain medium, and the average output power is between 0-400W.

[0012] Preferably, the matrix of the laser gain medium of the present invention is doped with Ho 3+ Single crystal or ceramic of YAG or Y2O3 or Lu2O3 containing Ho 3+ The doping concentration of the ions is between 0.2 and 10%, and the length of the crystal along the light propagation direction is between 2 and 15 mm.

[0013] Preferably, the first plano-convex mirror and the second plano-convex mirror are fixed by a mirror frame to form a beam expansion device, wherein the distance between the first plano-convex mirror and the second plano-convex mirror can be adjusted by a threaded device, and the distance between them is the sum of the focal lengths of the first plano-convex mirror and the second plano-convex mirror.

[0014] Preferably, the third plano-convex mirror of the present invention is fixed to a one-dimensional precision electric translation stage B, which can move along the laser propagation axis. The movement speed and direction of the one-dimensional precision electric translation stage B can be controlled by computer software programming.

[0015] Preferably, the axon of the present invention is a conical prism with a transmittance greater than 96% between 1900-2100 nm, which can focus light to multiple points on the optical axis to form an annular light beam.

[0016] Preferably, the laser resonant cavity of the present invention is a flat cavity shape, the input coupling mirror and the output coupling mirror are both plane mirrors, the input coupling mirror is coated with a two-color film layer, the transmittance between 1900-1960nm is greater than 96%, and the reflectivity between 1980-2150nm is greater than 99.6%, and the output coupling mirror is coated with a single-mode layer, and the transmittance between 1960-2200nm is between 2-15%.

[0017] Preferably, the present invention further comprises a chiral selection element and a tuning device placed at any position between the laser gain medium and the output coupling mirror, the chiral selection element and the tuning device comprising a base, a bracket, a rotating motor, an element fixing device and a chiral selection element, the bottom end of the bracket is fixedly arranged on the base, the top end of the bracket is fixed to the bottom end of the rotating motor, the element fixing device is fixed to the rotating shaft along the rotating shaft direction of the rotating motor, and the chiral selection element is fixed by the element fixing device; the chiral selection element is a filter or a transparent medium sheet with birefringence characteristics, which is a SiO2, YAG or CaF2 sheet, the thickness of the chiral selection element is between 0.5-1 mm, and the adjustment range of the inclination angle θ thereof with respect to the laser propagation direction is between -90 and 90 degrees;

[0018] When the tilt angle θ is 0 degrees, the plane where the chiral selection element is located is perpendicular to the optical axis, and the optical axis passes through the center of the chiral selection element. When the tilt angle θ is 90 degrees or -90 degrees, the chiral selection element is perpendicular to the vertical direction. At this time, the plane where the chiral selection element is located is lower than the optical axis, that is, the optical axis does not pass through the chiral selection element.

[0019] A method for generating high-power mid-infrared lasers with multiple transverse modes comprises the following steps:

[0020] ① Generate pump laser from pump source, adjust the position of the first plano-convex mirror to collimate the pump laser, and adjust the position of the second plano-convex mirror to collimate the pump beam onto the aconic lens; after the Bessel annular beam generated by the aconic lens is focused by the third convex lens, the annular beam enters the laser resonant cavity composed of the input coupling mirror and the output coupling mirror and is focused onto the laser gain medium, adjust the angles of the input coupling mirror and the output coupling mirror to be perpendicular to the axis angle of the pump laser propagation, so that the pump laser oscillates back and forth multiple times in the laser resonant cavity to obtain laser output;

[0021] ② The position of the one-dimensional precision electric translation stage A is roughly adjusted to make the laser gain medium at the focusing position of the annular beam. The position of the one-dimensional precision electric translation stage A is controlled by a computer to make the laser gain medium at the central circular hole position after the annular beam is focused. At this time, the cross section of the laser gain medium is irradiated by the annular pump laser, thereby generating a high-power annular vortex beam with a wavelength of 2.1μm.

[0022] ③ Precisely adjust the position of the one-dimensional precision electric translation stage A so that the laser gain medium is at the boundary positions on both sides of the central circular hole after the annular beam is focused. At this time, the cross section of half the length of the laser gain medium is irradiated by the annular pump laser, and the cross section of the other half is irradiated by the fundamental mode Gaussian beam, thereby generating a high-power flat-top Gaussian beam with a wavelength of 2.1μm;

[0023] ④ Precisely adjust the position of the one-dimensional precision electric translation stage A so that the laser gain medium is completely at the two ends of the central circular hole after the annular beam is focused. At this time, the entire cross section of the laser gain medium in the length direction is irradiated by the fundamental mode Gaussian beam, thereby generating a high-power fundamental mode Gaussian beam with a wavelength of 2.1μm;

[0024] ⑤ Precision adjust the position of the one-dimensional precision electric translation stage A so that the laser gain medium is in the middle position between step ③ and step ④. The test result should be a mixture of a high-power annular vortex beam and a high-power flat-top Gaussian beam.

[0025] By controlling the rotation angle of the rotary motor to adjust the inclination angle θ between the chirality selection element and the axis of the laser propagation direction, the chirality of the annular vortex beam obtained in step ② can be switched between left-handed and right-handed;

[0026] Changing the ratio of the focal length f2 of the second plano-convex mirror to the focal length f1 of the first plano-convex mirror in the beam expansion device can change the size of the spot diameter 2R output by the aconic lens;

[0027] By controlling the axis cone angle α of the axicon, the refractive index n, the spot diameter 2R input to the axicon through the second plano-convex mirror, and the distance L from the axicon to the third convex lens, the ring width t and the outer diameter d of the resulting Bessel annular beam can be controlled. r , and satisfy the following relations respectively:

[0028]

[0029]

[0030] Compared with the prior art, the present invention can achieve the following beneficial effects by automatically controlling the position of the one-dimensional precision electric translation stage A and the laser gain medium after the annular light generated by the axon lens passes through the laser resonant cavity:

[0031] (1) The device of the present invention can directly generate a variety of typical transverse mode beams, such as high-power annular vortex beams, high-power flat-top Gaussian beams, high-power fundamental mode Gaussian beams, etc. The obtained annular light is pure vortex light, and the chirality is controllable, with better processing accuracy and improved processing efficiency. By switching various transverse modes, the types of laser processing spots are increased, which greatly expands the types of objects that can be processed by high-precision lasers;

[0032] (2) The method of the present invention can switch the output light spot mode by simply moving the relative positions of the laser gain medium and the conical lens. When the laser gain medium is moved to the middle position of the beam hole, a vortex beam can be output; when the laser gain medium is at the left and right edges of the beam hole, a flat-top beam can be output; when the laser gain medium is at the left and right sides of the beam hole, a Gaussian beam can be output. The method does not require the addition or subtraction of components, is low in cost, can quickly and efficiently realize the switching of high-power mid-infrared laser modes, and significantly improves the efficiency of laser processing.

[0033] (3) Compared with the spatial light modulator (SLM) used in the existing scheme, the beam transformation element used in the present invention has the characteristics of a high damage threshold, and the ring laser pumping scheme adopted significantly reduces the thermal effect of the laser, making it easy to obtain high-power high-order mode laser output of nearly 100 watts, further improving the processing efficiency.

[0034] (4) The annular light beam generated by the present invention is a pure coherent vortex laser. Compared with the incoherent annular light beam of the existing device, it has orbital angular momentum, and its size and direction are controllable. Laser with this characteristic can have a self-polishing effect on the processing surface, prevent splashing, avoid the formation of plasma, and further improve the accuracy and efficiency of laser processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is a diagram of a device for generating high-power mid-infrared beams of multiple transverse modes in Example 1 of the present invention;

[0036] Figure 2 yes Figure 1 A schematic diagram of the structure of the chiral selection element and the tuning device;

[0037] Figure 3 yes Figure 2 Side view during angle adjustment;

[0038] Figure 4 yes Figure 1 Schematic diagram of the structure of the chiral selection element;

[0039] Figure 5 is the vortex beam generated when the laser gain medium of Example 1 of the present invention is located at the central circular hole position;

[0040] Figure 6 It is a flat-top beam generated when the laser gain medium of Example 1 of the present invention is located at the boundary positions on both sides of the central circular hole, wherein (a) is a flat-top beam generated when the laser gain medium is located at the boundary position on one side of the central circular hole, and (b) is a flat-top beam generated when the laser gain medium is located at the boundary position on the other side of the central circular hole;

[0041] Figure 7are Gaussian beams generated when the laser gain medium of Example 1 of the present invention is located at both ends of the central circular hole, wherein (a) is a Gaussian beam generated when the laser gain medium is located at one end boundary of the central circular hole, and (b) is a Gaussian beam generated when the laser gain medium is located at the other end boundary of the central circular hole;

[0042] Figure 8 The present invention generates spot diagrams and power curve diagrams of three types of light beams, namely, a vortex beam, a flat-top beam, and a Gaussian beam, wherein: (a) is the spot diagram of the vortex beam, and (b) is the power curve diagram corresponding to the vortex beam;

[0043] (c) is the spot diagram of Gaussian beam and annular beam, (d) is the power curve diagram corresponding to Gaussian beam and annular beam;

[0044] (e) is the spot diagram of the flat-top beam, and (f) is the power curve corresponding to the flat-top beam;

[0045] (g) is the spot diagram of the Gaussian beam, and (h) is the power curve corresponding to the Gaussian beam;

[0046] Fig. 9 is a simulation diagram of the interference between the vortex light and the plane wave generated by the present invention, wherein (a) is the vortex laser in LG 01 Interference diagram of the vortex laser in LG mode. (b) -1 Interference pattern in the mode.

[0047] In the figure: 1. pump source, 2. first plano-convex mirror, 3. second plano-convex mirror, 4. conical lens, 5. third plano-convex mirror, 6. one-dimensional precision electric translation stage B, 7. input coupling mirror, 8. laser gain medium, 9. one-dimensional precision electric translation stage A, 10. chiral selection element and tuning device, 101. base, 102. bracket, 103. rotating motor, 104. element fixing device, 105. chiral selection element, 11. output coupling mirror, 12. beam expansion device. DETAILED DESCRIPTION

[0048] The present invention will be further described below in conjunction with the accompanying drawings.

[0049] like Figure 1 As shown, a high-power mid-infrared laser generating device with multiple transverse modes includes a pump source 1 for providing horizontal laser light, the pump source 1 is a fiber laser outputted by a 1940nm single-mode fiber or a semiconductor laser coupled to a single-mode fiber, the output wavelength of which matches the absorption wavelength of a laser gain medium 8, and the average output power thereof is between 0-400W; and also includes a first plano-convex mirror 2, a second plano-convex mirror 3, a conical lens 4, a third plano-convex mirror 5, an input coupling mirror 7, a laser gain medium 8, and an output coupling mirror 11 coaxially arranged along the laser direction;

[0050] The first plano-convex mirror 2 is used to collimate and focus the laser generated by the pump source 1 onto the second plano-convex mirror 3;

[0051] The second plano-convex mirror 3 is used to collimate and focus the light beam focused by the first plano-convex mirror 2 onto the conical lens 4. The Bessel ring light beam generated by the conical lens 4 passes through the third plano-convex mirror 5 and is focused into the laser resonant cavity composed of the input coupling mirror 7 and the output coupling mirror 11. The laser passing through the gain medium 8 produces a particle number inversion and oscillates back and forth between the input coupling mirror 7 and the output coupling mirror 11. Part of the laser is output through the output coupling mirror 11 to obtain a high-power mid-infrared laser. The conical lens 4 is a conical prism with a transmittance greater than 96% between 1900-2100nm. It can focus light to multiple points on the optical axis to form a ring light beam.

[0052] The laser gain medium 8 is fixed to the one-dimensional precision electric translation stage A9, which can move along the laser propagation axis. The movement speed and direction of the one-dimensional precision electric translation stage A9 can be controlled by computer software programming, which is a well-known technical means for those skilled in the art.

[0053] The matrix of laser gain medium 8 is doped with Ho 3+ Single crystal or ceramic of YAG or Y2O3 or Lu2O3 containing ions, where Ho 3+ The doping concentration of the ions is between 0.2% and 10%, and the length of the crystal along the light propagation direction is between 2 and 15 mm.

[0054] The first plano-convex mirror 2 and the second plano-convex mirror 3 are fixed by a mirror frame to form a beam expansion device 12, wherein the distance between the first plano-convex mirror 2 and the second plano-convex mirror 3 can be adjusted by a threaded device, and the distance between them is the sum of the focal lengths of the first plano-convex mirror 2 and the second plano-convex mirror 3.

[0055] The third plano-convex mirror 5 is fixed to a one-dimensional precision electric translation stage B6. The one-dimensional precision electric translation stage B6 can move along the laser propagation axis. The movement speed and direction of the one-dimensional precision electric translation stage B6 can be controlled by computer software programming.

[0056] The laser resonant cavity is a flat cavity shape, the input coupling mirror 7 and the output coupling mirror 11 are both plane mirrors, the input coupling mirror 7 is coated with a two-color film layer, the transmittance between 1900-1960nm is greater than 96%, and the reflectivity between 1980-2150nm is greater than 99.6%, and the output coupling mirror 11 is coated with a single-mode layer, and the transmittance between 1960-2200nm is between 2-15%.

[0057] like Figure 2-Figure 4As shown, the present invention also includes a chiral selection element and tuning device 10 placed at any position between the laser gain medium 8 and the output coupling mirror 11, and the chiral selection element and tuning device 10 include a base 101, a bracket 102, a rotating motor 103, an element fixing device 104 and a chiral selection element 105. The bottom end of the bracket 102 is fixedly arranged on the base 101, the top end of the bracket 102 is fixed to the bottom end of the rotating motor 103, the element fixing device 104 is fixed to the rotating shaft along the rotating shaft direction of the rotating motor 103, and the chiral selection element 105 is fixed by the element fixing device 104; the chiral selection element 105 is a filter or a transparent medium sheet with birefringence characteristics, which is a SiO2, YAG or CaF2 sheet, the thickness of the chiral selection element 105 is between 0.5-1mm, and the adjustment range of the inclination angle θ thereof with the laser propagation direction is between -90-90 degrees;

[0058] When the tilt angle θ is 0 degrees, the plane where the chiral selection element 105 is located is perpendicular to the optical axis, and the optical axis passes through the center of the chiral selection element 105. When the tilt angle θ is 90 degrees or -90 degrees, the chiral selection element 105 is perpendicular to the vertical direction. At this time, the plane where the chiral selection element 105 is located is lower than the optical axis, that is, the optical axis does not pass through the chiral selection element.

[0059] A method for generating high-power mid-infrared lasers with multiple transverse modes, comprising the following steps:

[0060] ① A pump source 1 generates a pump laser, and the position of the first plano-convex mirror 2 is adjusted to collimate the pump laser. The position of the second plano-convex mirror 3 is adjusted to collimate the pump beam onto the aconic lens 4. After the Bessel annular beam generated by the aconic lens 4 is focused by the third convex lens 5, the annular beam enters the laser resonant cavity formed by the input coupling mirror 7 and the output coupling mirror 11 and is focused onto the laser gain medium 8. The angles of the input coupling mirror 7 and the output coupling mirror 11 are adjusted to be perpendicular to the axis of the pump laser propagation, so that the pump laser oscillates back and forth multiple times in the laser resonant cavity to obtain laser output.

[0061] ② The position of the one-dimensional precision electric translation stage A9 is roughly adjusted to make the laser gain medium 8 at the position where the annular beam is focused. The position of the one-dimensional precision electric translation stage A9 is controlled by a computer to make the laser gain medium 8 at the central circular hole position after the annular beam is focused. At this time, the cross section of the laser gain medium 8 is irradiated by the annular pump laser, thereby generating a high-power annular vortex beam output with a wavelength of 2.1 μm;

[0062] ③ The position of the one-dimensional precision electric translation stage A9 is precisely adjusted to make the laser gain medium 8 be located at the boundary positions on both sides of the central circular hole after the annular beam is focused. At this time, the cross section of half the length of the laser gain medium 8 is irradiated by the annular pump laser, and the cross section of the other half is irradiated by the fundamental mode Gaussian beam, thereby generating a high-power flat-top Gaussian beam output with a wavelength of 2.1μm;

[0063] ④ Precisely adjust the position of the one-dimensional precision electric translation stage A9 so that the laser gain medium 8 is completely at the two ends of the central circular hole after the annular beam is focused. At this time, the entire cross section of the laser gain medium 8 in the length direction is irradiated by the fundamental mode Gaussian beam, thereby generating a high-power fundamental mode Gaussian beam output with a wavelength of 2.1μm;

[0064] ⑤ Precisely adjust the position of the one-dimensional precision electric translation stage A9 so that the laser gain medium 8 is in the other intermediate position between step ③ and step ④. The test result should be a mixture of a high-power annular vortex beam and a high-power flat-top Gaussian beam.

[0065] By controlling the rotation angle of the rotary motor 103 and precisely adjusting the inclination angle θ between the chirality selection element 105 and the axis of the laser propagation direction, the chirality of the vortex beam obtained in step ② can be switched between left-handed and right-handed;

[0066] Changing the ratio of the focal length f2 of the second plano-convex mirror 3 to the focal length f1 of the first plano-convex mirror 2 in the beam expansion device 12 can change the size of the spot diameter 2R output through the aconic lens 4;

[0067] By controlling the axis cone angle α of the aconic lens 4, the refractive index n, the spot diameter 2R input to the aconic lens 4 through the second plano-convex mirror 3, and the distance L from the aconic lens 4 to the third convex lens 5, the ring width t and the outer diameter d of the obtained Bessel annular beam can be controlled. r , and satisfy the following relations respectively:

[0068]

[0069]

[0070] Example 1

[0071] like Figure 1 As shown, a high-power mid-infrared laser generating device with multiple transverse modes specifically comprises:

[0072] Pump source 1 is a 1940nm continuous fiber laser (single-mode 200W), which outputs the fundamental transverse mode pump laser. The generated pump light excites the laser gain medium 8 to generate a 2μm band laser output, with a collimated spot of 3mm, M 2 =1.5;

[0073] The focal length of the first plano-convex mirror 2 is 20 mm, and the focal length of the second plano-convex mirror 3 is 100 mm. The pump light generated by the pump source 1 is collimated. The first plano-convex mirror 2 and the second plano-convex mirror 3 constitute a focusing-collimating system.

[0074] The aconic lens 4 refracts the fundamental mode output laser of the 1940nm single-mode fiber laser to output Bessel ring light, and the third plano-convex mirror 5 focuses the ring light and outputs it into the laser resonant cavity;

[0075] The laser gain medium 8 used is Ho:Y2O3, where Ho 3+ The ion doping concentration is 2%. The one-dimensional precision electric translation stage A9 is moved to the position of the first annular beam center hole through computer precision control. Figure 5 As shown, the first function of the present invention is realized, and a high-power annular vortex beam is output;

[0076] The output coupling mirror 11 is a flat mirror, and the coupling output rate is 10%;

[0077] The distance and angle of the cavity mirrors in the laser resonant cavity of the present invention meet the conditions for stable laser resonance. By using the fiber laser Pu laser gain medium described above, the distance L between the laser gain medium 8 and the third plano-convex mirror 5 is controlled by controlling the one-dimensional precision electric translation stage A9, and high-power mid-infrared lasers with multiple transverse modes can be directly generated.

[0078] In order to further illustrate the method of directly generating multiple transverse modes of high-power mid-infrared lasers in this embodiment, it is now described in detail with reference to the accompanying drawings and specific examples as follows:

[0079] like Figure 1 As shown, firstly, a high-power fiber laser with an operating wavelength of 1940 nm is used as a pump source 1, and the pump beam is collimated after passing through the first plano-convex mirror 2 and the second plano-convex mirror 3. The collimated laser generates annular light through the birefringence effect of the axle lens 4, and the annular light is focused by the third plano-convex mirror 5 onto the Ho:Y2O3 laser gain medium 8 and absorbed by the laser gain medium 8 to generate a population inversion;

[0080] Next, the distance between the one-dimensional precision electric translation stage A9 on which the laser gain medium 8 is placed and the third plano-convex mirror 5 is precisely controlled so that the position of the laser gain medium 8 is located at the center of the Bessel ring laser focusing beam waist, as shown in the following example: Figure 5 As shown, at this time, the pump light irradiated on the laser gain medium 8 is a ring laser. Through the matching of the laser mode with the emitted 2.1um wavelength in the laser resonant cavity and the cylindrical symmetric flat cavity type used as the entire cavity, a vortex beam with a ring-shaped distribution of light intensity is finally obtained, as shown in FIG. Figure 8 As shown in (a)-(b).

[0081] A CCD camera (WinCamD-IR-BB, pixel size 17 μm) was used to monitor the interference fringes of the Mach-Zehnder (MZ) interferometer to determine whether the vortex laser generated by the laser had chirality. When the tilt angle θ of the chiral selection element 105 was in the range of 2-4°, the generated vortex laser was LG 01 The interference results are shown in Fig. 9 (a), the stripes have upward bifurcations; when the tilt angle θ of the chiral selection element 105 is in the range of -2°-(-4°), LG -1 Mode of vortex laser, such as Fig. 9 (b) shows vertical stripes that fork downward.

[0082] In this embodiment, the position of the third convex lens 5 in the z-axis direction can be changed by precisely adjusting the position of the one-dimensional precision electric translation stage B, which can also achieve the above-mentioned effect, which will not be described in detail in the following embodiments.

[0083] Example 2

[0084] Unless otherwise stated, the device parameters in this embodiment are the same as those in Embodiment 1.

[0085] like Figure 1 As shown, a high-power mid-infrared laser generating device with multiple transverse modes specifically comprises:

[0086] The pump source 1 is a 1940nm continuous fiber laser (single-mode 300W), which outputs a pump laser in the fundamental transverse mode. The generated pump light excites the laser gain medium 8 to generate a laser output in the 2.1μm band.

[0087] The position of the one-dimensional precision electric translation stage A9 is precisely adjusted by a computer so that the center of the laser gain medium 8 is located at the left and right sides of the hole edge of the cross-sectional view of the pump light in the z-axis direction, as shown in FIG. Figure 6 As shown in (a) and (b), the second function of the present invention is realized, that is, a high-power flat-top Gaussian beam is output.

[0088] In order to further illustrate the method of directly generating multiple transverse modes of high-power mid-infrared lasers in this embodiment, it is now described in detail with reference to the accompanying drawings and specific examples as follows:

[0089] like Figure 1 As shown, first, the fiber laser generated by the working wavelength of 1940nm of the pump source 1 is collimated after passing through the first plano-convex mirror 2 and the second plano-convex mirror 3 with the same focal length. The collimated laser produces annular light through the birefringence effect of the conical lens 4. The annular light beam is focused onto the laser gain medium 8 by the third plano-convex mirror 5, and is absorbed by the gain medium to produce a population inversion. By adjusting the deviation angle of the output coupling mirror 11 and the laser in the laser resonant cavity, the angle of the cavity mirror is appropriately adjusted to generate laser oscillation.

[0090] Precisely adjust the position of the one-dimensional precision electric translation stage A9, as follows Figure 8 As shown in (e) and (f), the laser gain medium 8 is located at the boundary positions on both sides of the central circular hole after the annular light beam is focused. At this time, the cross section of half the length of the laser gain medium 8 is irradiated by the annular pump laser, so that the annular light passes through the laser gain medium to output a flat-top light. The cross section of the other half of the length of the position where the gain medium and the light beam are located is irradiated by the fundamental mode Gaussian beam, thereby generating a high-power flat-top Gaussian beam with a wavelength of 2.1μm.

[0091] In this embodiment, the tilt angle θ of the chiral selection element 105 can be at 0° or any other state, and the angle can also be adjusted to 90 degrees or -90 degrees. At this time, the laser does not pass through the chiral selection element 105, which has no substantial impact on the effect to be achieved in this embodiment.

[0092] Example 3

[0093] like Figure 1 As shown, a high-power mid-infrared laser generating device with multiple transverse modes, the specific elements of which are the same as those in Example 1.

[0094] By precisely adjusting the position of the one-dimensional precision electric translation stage A9, the laser gain medium 8 is completely located at the two ends of the central circular hole after the annular beam is focused. Figure 7 As shown in (a) and (b), at this time, the cross section of the entire gain medium in the length direction is irradiated by the fundamental mode Gaussian beam, thereby generating a high-power fundamental mode Gaussian beam with a wavelength of 2.1 μm, as shown in Figure 8 As shown in (g) and (h).

[0095] In this embodiment, the tilt angle θ of the chiral selection element 105 can be at 0° or any other state, and the angle can also be adjusted to 90 degrees or -90 degrees. At this time, the laser does not pass through the chiral selection element 105, which has no substantial impact on the effect to be achieved in this embodiment.

[0096] Example 4

[0097] like Figure 1 As shown, a high-power mid-infrared laser generating device with multiple transverse modes, the specific elements of which are the same as those in Example 1.

[0098] By precisely adjusting the position of the one-dimensional precision electric translation stage A9, the laser gain medium 8 is placed between the two side boundaries of the central circular hole after the annular beam is focused and the center of the hole. The laser obtained is a combination state of Gaussian beam and annular beam in any proportion, as shown in FIG. Figure 8 As shown in (c) and (d).

[0099] In this embodiment, the tilt angle θ of the chiral selection element 105 can be at 0° or any other state, and the angle can also be adjusted to 90 degrees or -90 degrees. At this time, the laser does not pass through the chiral selection element 105, which has no substantial impact on the effect to be achieved in this embodiment.

Claims

1. A high-power mid-infrared laser generating device with multiple transverse modes, comprising a pump source (1) for providing horizontal laser light, characterized in that: It also includes a first plano-convex mirror (2), a second plano-convex mirror (3), an aconical lens (4), a third plano-convex mirror (5), an input coupling mirror (7), a laser gain medium (8), and an output coupling mirror (11) which are coaxially arranged along the laser direction; The first plano-convex mirror (2) is used to collimate and focus the laser light generated by the pump source (1) onto the second plano-convex mirror (3); The second plano-convex mirror (3) is used to collimate and focus the light beam focused by the first plano-convex mirror (2) onto the aconic lens (4); the Bessel annular light beam generated by the aconic lens (4) passes through the third plano-convex mirror (5) and is focused into a laser resonant cavity formed by an input coupling mirror (7) and an output coupling mirror (11); the laser light passing through the laser gain medium (8) generates a population inversion and oscillates back and forth between the input coupling mirror (7) and the output coupling mirror (11); part of the laser light is output through the output coupling mirror (11) to obtain a high-power mid-infrared laser; The laser gain medium (8) is fixed to a one-dimensional precision electric translation stage A (9), and the one-dimensional precision electric translation stage A (9) is capable of moving along the laser propagation axis.

2. The high-power mid-infrared laser generating device with multiple transverse modes according to claim 1, characterized in that: The pump source (1) is a fiber laser with 1940nm single-mode fiber output or a semiconductor laser coupled to a single-mode fiber, the output wavelength matches the absorption wavelength of the laser gain medium (8), and the average output power is between 0-400W.

3. The high-power mid-infrared laser generating device with multiple transverse modes according to claim 1, characterized in that: The matrix of the laser gain medium (8) is doped with Ho 3+ Single crystal or ceramic of YAG or Y2O3 or Lu2O3 containing Ho 3+ The doping concentration of the ions is between 0.2 and 10%, and the length of the crystal along the light propagation direction is between 2 and 15 mm.

4. The high-power mid-infrared laser generating device with multiple transverse modes according to claim 1, characterized in that: A first plano-convex mirror (2) and a second plano-convex mirror (3) are fixed by a mirror frame to form a beam expansion device (12); the distance between the first plano-convex mirror (2) and the second plano-convex mirror (3) is adjusted by a threaded device, and the distance between them is the sum of the focal lengths of the first plano-convex mirror (2) and the second plano-convex mirror (3).

5. The high-power mid-infrared laser generating device with multiple transverse modes according to claim 1, characterized in that: The third plano-convex mirror (5) is fixed to a one-dimensional precision electric translation stage B (6), and the one-dimensional precision electric translation stage B (6) is capable of moving along the laser propagation axis.

6. The high-power mid-infrared laser generating device with multiple transverse modes according to claim 1, characterized in that: The aconic lens (4) is a conical prism with a transmittance greater than 96% between 1900 and 2100 nm.

7. The high-power mid-infrared laser generating device with multiple transverse modes according to claim 1, characterized in that: The laser resonant cavity is a flat cavity shape, the input coupling mirror (7) and the output coupling mirror (11) are both plane mirrors, the input coupling mirror (7) is plated with a two-color film layer, the transmittance between 1900-1960nm is greater than 96%, and the reflectivity between 1980-2150nm is greater than 99.6%, and the output coupling mirror (11) is plated with a single-mode layer, the transmittance between 1960-2200nm is between 2% and 15%.

8. The high-power mid-infrared laser generating device with multiple transverse modes according to claim 1, characterized in that: Also included is a chiral selection element and tuning device (10) placed at any position between the laser gain medium (8) and the output coupling mirror (11), the chiral selection element and tuning device (10) comprising a base (101), a bracket (102), a rotating motor (103), an element fixing device (104) and a chiral selection element (105), the bottom end of the bracket (102) being fixedly arranged on the base (101), the top end of the bracket (102) being fixedly arranged on the bottom end of the rotating motor (103) The element fixing device (104) is fixed to the rotating shaft of the rotating motor (103) along the rotating shaft direction, and the chiral selection element (105) is fixed by the element fixing device (104); the chiral selection element (105) is a filter or a transparent medium sheet with birefringence characteristics, which is a SiO2, YAG or CaF2 sheet. The thickness of the chiral selection element (105) is between 0.5-1mm, and the adjustment range of the inclination angle θ thereof with respect to the laser propagation direction is between -90 and 90 degrees.

9. A method for generating high-power mid-infrared lasers with multiple transverse modes, characterized in that: The following steps are involved: ① A pump source (1) generates a pump laser, the position of the first plano-convex mirror (2) is adjusted to collimate the pump laser, the position of the second plano-convex mirror (3) is adjusted to collimate the pump beam onto the aconical lens (4), the Bessel annular beam generated by the aconical lens (4) is focused by the third convex lens (5), the annular beam enters a laser resonant cavity formed by an input coupling mirror (7) and an output coupling mirror (11) and is focused onto a laser gain medium (8), the angles of the input coupling mirror (7) and the output coupling mirror (11) are adjusted to be perpendicular to the axial angle of the pump laser propagation, so that the pump laser oscillates back and forth multiple times in the laser resonant cavity to obtain laser output; ② Roughly adjusting the position of the one-dimensional precision electric translation stage A (9) so that the laser gain medium (8) is at the position where the annular beam is focused, and controlling the position of the one-dimensional precision electric translation stage A (9) by a computer so that the laser gain medium (8) is at the central circular hole position after the annular beam is focused. At this time, the cross section of the laser gain medium (8) is irradiated by the annular pump laser, generating a high-power annular vortex beam with a wavelength of 2.1 μm; ③ The position of the one-dimensional precision electric translation stage A (9) is precisely adjusted so that the laser gain medium (8) is located at the boundary positions on both sides of the central circular hole after the annular beam is focused. At this time, the cross section along half of the length of the laser gain medium (8) is irradiated by the annular pump laser, and the cross section along the other half of the length is irradiated by the fundamental mode Gaussian beam, thereby generating a high-power flat-top Gaussian beam with a wavelength of 2.1 μm; ④ Precisely adjust the position of the one-dimensional precision electric translation stage A (9) so that the laser gain medium (8) is completely located at the two ends of the central circular hole after the annular beam is focused. At this time, the entire cross section of the laser gain medium (8) in the length direction is irradiated by the fundamental mode Gaussian beam, generating a high-power fundamental mode Gaussian beam with a wavelength of 2.1 μm; ⑤ Precisely adjust the position of the one-dimensional precision electric translation stage A (9) so that the laser gain medium (8) is in another intermediate position between step ③ and step ④. The test result is a mixture of a high-power annular vortex beam and a high-power flat-top Gaussian beam.

10. The method for generating a high-power mid-infrared laser with multiple transverse modes according to claim 9, characterized in that: By precisely controlling the rotation angle of the rotary motor (103) and adjusting the inclination angle θ between the chirality selection element (105) and the axis of the laser propagation direction, the chirality of the high-power annular vortex beam obtained in step ② can be switched between left-handed and right-handed; The size of the diameter 2R of the light spot outputted through the aconic lens (4) is changed by changing the ratio of the focal length f2 of the second plano-convex mirror (3) and the focal length f1 of the first plano-convex mirror (2) in the light beam expansion device (12); By controlling the axis cone angle α of the aconic lens (4), the refractive index n, the diameter 2R of the light spot input to the aconic lens (4) via the second plano-convex mirror (3), and the distance L from the aconic lens (4) to the third convex lens (5), the ring width t and the outer diameter d of the obtained Bessel annular light beam can be controlled. r , and satisfy the following relations respectively:

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