High-order superposition state lg mode generating device and generating method

Abstract

The application discloses a high-order superposition state LG mode generating device and method, relates to the optical and laser technical field, and comprises a pump light source, a first plano-convex lens, a cone lens, a second plano-convex lens and a laser resonant cavity; the laser resonant cavity is composed of a gain medium, a third plano-convex lens and a plane mirror; the pump light source generates laser, the laser is collimated to the cone lens through the first plano-convex lens, the generated Bessel ring-shaped light beam is focused into the laser gain medium through the second plano-convex lens, the gain medium is excited to generate a ring-shaped vortex light beam, after passing through the third plano-convex lens, part of the laser oscillates in the laser resonant cavity, and the high-order superposition state LG mode is output through the plane mirror, namely the output coupling mirror of the laser resonant cavity. The application provides a simple, convenient, compact, low-precision control demand and high-conversion-efficiency solid vortex light laser (high-order superposition state LG mode generating device) to realize the generation of super-high-order number LG vortex light beams.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optics and laser technology, in particular to a high-order superposition state LG mode generating device and method. BACKGROUND

[0002] As a typical high-order mode, the vortex beam is annularly distributed in space and has orbital angular momentum characteristics, and can be used for the transmission of angular momentum between micro-particles or atoms. In recent years, it has shown considerable advantages in multi-trap optical tweezers, micro-nano processing and high-efficiency and high-precision laser processing. Higher-order optical vortices have great application prospects in high-angular-momentum quantum entanglement and high-sensitivity spatial measurement. The journal paper “Generating High-Charge Optical Vortices Directly from Laser Up to 288th Order” generates high-order LG modes by etching a circular pattern on the surface of a laser cavity mirror and introducing low-order mode loss in the resonant cavity. The journal paper “Ultra-High-Order Laguerre–Gaussian Field Generated Directly From a Laser Cavity with Spherical Aberration” introduces a method for directly generating ultra-high-order Laguerre-Gaussian modes using the spherical aberration of a lens in a laser cavity. This method is based on an end-pumped Nd:YVO4 laser, and two lenses with focal lengths of 150 mm and 51.8 mm are added to the resonant cavity. The spherical aberration of the 51.8 mm focal length lens is used to select the mode in the cavity, thereby realizing the output of high-order LG modes.

[0003] Due to the instability of high-order modes, how to controllably generate high-order modes is a difficult problem in the field of vortex light. The existing scheme of etching a pattern on the surface of the cavity mirror to suppress low-order modes has the problem of large loss and difficulty in obtaining high-power vortex beam output. The existing scheme of adding optical elements in the cavity for mode selection has the problems of long laser resonant cavity length, many added optical elements, and high requirement for element precision when obtaining higher-order LG modes. SUMMARY

[0004] The technical problem to be solved by the present application is to overcome the defects of low output power, low output mode purity, and complex device in the prior art when directly generating high-order LG vortex beams in a solid-state laser, and to provide a simple and convenient, compact, and high-conversion-efficiency solid-state vortex laser (high-order superposition state LG mode generating device) to realize the generation of ultra-high-order LG vortex beams.

[0005] In one aspect, a high-order superposition state LG mode generating device comprises the following:

[0006] The device comprises, in sequence, a pump light source, a first plano-convex lens, a conical lens, a second plano-convex lens, and a laser resonant cavity.

[0007] The pump light source generates horizontal pump laser and outputs to the first plano-convex lens.

[0008] The first plano-convex lens collimates and focuses the pump laser onto the conical lens.

[0009] The conical lens generates a Bessel ring-shaped beam and outputs to the second plano-convex lens.

[0010] The second plano-convex lens focuses the Bessel ring-shaped beam into a laser gain medium.

[0011] The laser resonant cavity is composed of the laser gain medium, a third plano-convex lens, and a plane mirror. The front end of the laser gain medium is coated as an input coupling mirror, and the plane mirror is coated as an output coupling mirror. The Bessel ring-shaped beam entering the laser resonant cavity excites the laser gain medium to generate a ring-shaped vortex beam. The ring-shaped vortex beam that meets the oscillation condition oscillates back and forth in the laser resonant cavity after passing through the third plano-convex lens, generating a high-order superposition state LG mode, which is output through the output coupling mirror.

[0012] Preferably, the pump light source is a single-mode fiber laser or a single-mode fiber-coupled semiconductor laser. The output wavelength of the pump light source matches the absorption wavelength of the laser gain medium, and the wavelength of the pump light source is between 400 and 2100 nm. The average output power of the pump light source is between 0 and 400 W.

[0013] Preferably, the distance between the first plano-convex lens and the light source output end of the pump light source is the focal length of the first plano-convex lens.

[0014] Preferably, the conical lens is a circular conical prism.

[0015] Preferably, the substrate of the laser gain medium comprises tungstate KGW, potassium lanthanum barium sodium fluoride KBLAN, yttrium vanadate YVO4, yttrium aluminum garnet YAG, yttrium lithium fluoride YLF, yttrium aluminum YAP, or glass GLASS. The yttrium vanadate YVO4, yttrium aluminum garnet YAG, yttrium lithium fluoride YLF, yttrium aluminum YAP, or glass GLASS is doped with rare earth ions at a concentration of between 0.2 and 10%. The length of the laser gain medium along the light propagation direction is between 2 and 15 mm.

[0016] Preferably, the focal length of the third plano-convex lens is between 10 and 40 mm.

[0017] Preferably, the laser resonant cavity is a plane-parallel cavity; the coated front end face of the laser gain medium is the end face of the laser gain medium facing the pump light source, the coating of the front end face of the laser gain medium is a dichromatic film layer; the coating of the plane mirror is a single film layer; the distance between the input coupling mirror and the output coupling mirror is greater than 10-20 mm of the focal length of the third plano-convex lens.

[0018] Preferably, the wavelength of the annular vortex beam generated by the excited laser gain medium is between 800 nm and 2100 nm.

[0019] Preferably, the high-order superposition state LG mode generating device further comprises a first multi-dimensional displacement stage and a second multi-dimensional displacement stage; the conical lens is fixed with the first multi-dimensional displacement stage, and the third plano-convex lens is fixed with the second multi-dimensional displacement stage; the first multi-dimensional displacement stage moves along the laser propagation axis, or moves horizontally or up and down along the plane perpendicular to the laser propagation axis; the second multi-dimensional displacement stage moves along the laser propagation axis, or moves horizontally or up and down along the plane perpendicular to the laser propagation axis.

[0020] In another aspect, a high-order superposition state LG mode generating method comprises the following specific steps:

[0021] S1, coaxially arranging a pump light source, a first plano-convex lens, a conical lens, a second plano-convex lens, a laser gain medium and a plane mirror according to the direction of the generated laser; the convex surfaces of the first plano-convex lens and the second plano-convex lens both face the pump light source; the conical surface of the conical lens faces away from the pump light source;

[0022] S2, generating pump laser by the pump light source, adjusting the position of the first plano-convex lens to collimate the pump laser to the conical lens, generating a Bessel annular beam by the pump laser passing through the conical lens, focusing the Bessel annular beam by the second convex lens to enter the laser gain medium, adjusting the angle of the laser gain medium and the plane mirror to make the end face of the laser gain medium and the mirror face of the plane mirror perpendicular to the axis of the pump laser propagation, and making the laser mode generated by the pump laser exciting the gain medium multiple times in the laser resonant cavity to obtain laser output;

[0023] S3, roughly adjusting the first multi-dimensional displacement stage to change the position of the conical lens, so that the Bessel annular beam is focused at the coated front end face of the laser gain medium, and then precisely adjusting the first multi-dimensional displacement stage to change the position of the conical lens, so that the center hole position of the focused Bessel annular beam is at the center of the coated front end face of the laser gain medium, enters the laser gain medium, and the Bessel annular beam excites the laser gain medium to generate an annular vortex beam;

[0024] S4, a third plano-convex lens is inserted into the laser resonant cavity close to the position of the plane mirror by using the second multi-dimensional displacement table, the convex surface of the third plano-convex lens faces the pump light source, the center of the third plano-convex lens is on the pump laser propagation axis, and the annular vortex light beam passes through the third plano-convex lens, and the annular vortex light meeting the oscillation condition oscillates in the laser resonant cavity multiple times;

[0025] S5, the second multi-dimensional displacement table is precisely adjusted, so that the third plano-convex lens slowly moves along the pump laser propagation axis to the direction where the laser gain medium is located, in the moving process, based on the spherical aberration effect of the third plano-convex lens, the output mode is converted from the fundamental mode Gaussian light beam to the multi-ring petal-shaped superimposed LG mode, and then to the single-ring high-order petal-shaped superimposed LG mode, and finally to the no-mode output; wherein the single-ring high-order petal-shaped superimposed LG mode is the required mode.

[0026] Compared with the prior art, the present application has the following beneficial effects:

[0027] (1) The present application provides a solid vortex light laser (high-order superimposed LG mode generating device) which is simple and convenient, compact in structure, has low demand for precise control, and has high conversion efficiency, to realize the generation of super-high-order LG vortex light beam.

[0028] (2) The present application uses a plano-convex lens in the laser resonant cavity, and utilizes the spherical aberration effect of the plano-convex lens to generate high-order superimposed LG mode in the laser resonant cavity. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 It is a structure diagram of a high-order superimposed LG mode generating device of an embodiment of the present application.

[0030] Figure 2 It is a flow chart of a high-order superimposed LG mode generating method of an embodiment of the present application. DETAILED DESCRIPTION

[0031] The present application will be further described below through specific embodiments.

[0032] As shown in the drawings, Figure 1 A high-order superimposed LG mode generating device, specifically as follows:

[0033] The high-order superimposed LG mode generating device comprises a pump light source 1 for providing horizontal direction laser, a first plano-convex lens 2, a conical lens 3, a second plano-convex lens 5, a laser gain medium 6, a third plano-convex lens 7 and a plane mirror 9 coaxially arranged along the direction of the laser generated by the pump light source 1, and a first multi-dimensional displacement table 4 and a second multi-dimensional displacement table 8.

[0034] The pump light source 1 is a single-mode fiber output fiber laser or a single-mode fiber-coupled semiconductor laser with a wavelength of 400-2100 nm, and the output wavelength matches the absorption wavelength of the laser gain medium 6. The average output power of the pump light source 1 is 0-400 W.

[0035] The first plano-convex lens 2 is used to collimate and focus the laser generated by the pump light source 1 onto the conical lens 3. The first plano-convex lens 2 is fixed by a mirror holder to achieve pump laser beam expansion. The first plano-convex lens 2 and the light source output end face of the pump light source 1 are adjusted by a threaded device, and the distance between them is the focal length of the first plano-convex lens 2.

[0036] The conical lens 3 is a conical prism with a transmittance of more than 99.5% for laser with a wavelength of 400-2100 nm. The conical lens 3 is fixed with the first multi-dimensional displacement table 4, and the second multi-dimensional displacement table 4 can move along the laser propagation axis, and can also move horizontally or vertically along the plane perpendicular to the laser propagation axis.

[0037] The second plano-convex lens 5 is fixed by a mirror holder to focus the pump laser that has passed through the conical lens.

[0038] The substrate of the laser gain medium 6 is one of common laser gain medium materials, including tungstate KGW, potassium lanthanum barium sodium fluoride KBLAN, yttrium vanadate YVO4, yttrium aluminum garnet YAG, yttrium lithium fluoride YLF, yttrium aluminum YAP or glass GLASS, wherein yttrium vanadate YVO4, yttrium aluminum garnet YAG, yttrium lithium fluoride YLF, yttrium aluminum YAP or glass GLASS is doped with rare earth ions with a concentration of 0.2-10%; the length of the laser gain medium crystal along the light propagation direction is 2-15 mm.

[0039] The focal length of the third plano-convex lens 7 is 10-40 mm; the third plano-convex lens 7 is fixed with the second multi-dimensional displacement table 8, and the second multi-dimensional displacement table 8 can move along the laser propagation axis, and can also move horizontally or vertically along the plane perpendicular to the laser propagation axis.

[0040] The composition and function of the laser resonator are as follows:

[0041] The laser resonant cavity is a parallel plane cavity, the coated front end surface of the gain medium 6 serving as an input coupling mirror of the laser resonant cavity, and the coated plane mirror 9 serving as an output coupling mirror of the laser resonant cavity; the front end surface of the gain medium 6 is coated with a dichromatic film layer, the transmittance of which is greater than 95% between 400 nm and 2100 nm, and the reflectance of which is greater than 99.6% between 800 nm and 2100 nm; the plane mirror 9 has a single film layer, the transmittance of which is between 2% and 15% between 800 nm and 2100 nm. The distance between the input coupling mirror and the output coupling mirror is greater than the focal length of the third plano-convex lens 7, 10-20 mm.

[0042] The Bessel ring-shaped light beam generated by the conical lens 3 is focused into the laser gain medium 6 after passing through the second plano-convex lens 5, the laser gain medium 6 generates particle number inversion, the Bessel ring-shaped light beam excites the laser gain medium 6 to generate a ring-shaped vortex light beam, and the laser mode satisfying the back-and-forth oscillation condition in the laser resonant cavity oscillates back and forth between the input coupling mirror and the output coupling mirror after passing through the third plano-convex lens 7, and the high-order superposition state LG mode is obtained by outputting through the output coupling mirror.

[0043] As shown in Figure 2 A high-order superposition state LG mode generation method, the specific steps are as follows:

[0044] S1, coaxially arrange the pump light source 1, the first plano-convex lens 2, the conical lens 3, the second plano-convex lens 5, the laser gain medium 6 and the plane mirror 9 according to the direction of the generated laser; the convex surfaces of the first plano-convex lens 2 and the second plano-convex lens 5 both face the pump light source 1; and the conical surface of the conical lens 3 faces away from the pump light source 1.

[0045] S2, generate pump laser by the pump light source 1, adjust the position of the first plano-convex lens 2 to collimate the pump laser to the conical lens 3, the Bessel ring-shaped light beam generated by the pump laser passing through the conical lens 3 is focused into the laser gain medium 6 after passing through the second plano-convex lens 5, and adjust the angle of the laser gain medium 6 and the plane mirror 9 to make the end surface of the laser gain medium 6 and the mirror surface of the plane mirror 9 perpendicular to the axis of the pump laser propagation, so that the pump laser oscillates back and forth in the laser resonant cavity to obtain laser output.

[0046] S3, first roughly adjust the first multi-dimensional displacement table to change the position of the conical lens 3, so that the Bessel ring-shaped light beam is focused at the coated front end surface of the laser gain medium 6, and then precisely adjust the first multi-dimensional displacement table to change the position of the conical lens 3, so that the center hole position of the Bessel ring-shaped light beam after focusing is at the center of the coated front end surface of the laser gain medium 6, and the Bessel ring-shaped light beam enters the laser gain medium 6, exciting the laser gain medium 6 to generate a ring-shaped vortex light beam.

[0047] S4, a second multi-dimensional displacement table is used to insert the third plano-convex lens 7 into the position close to the plane mirror 9 of the laser resonant cavity, the convex surface of the third plano-convex lens 7 faces the pump light source 1, and the center of the third plano-convex lens 7 is on the pump laser propagation axis, so that the annular vortex light beam passes through the third plano-convex lens 7, and the annular vortex light meeting the oscillation condition oscillates in the laser resonant cavity multiple times.

[0048] S5, the second multi-dimensional displacement table is precisely adjusted, so that the third plano-convex lens 7 slowly moves along the pump laser propagation axis to the direction where the laser gain medium 6 is located, in the moving process, based on the spherical aberration effect of the third plano-convex lens 7, the output mode is converted from the fundamental mode Gaussian light beam to the multi-ring petal-shaped superimposed LG mode, then to the single-ring high-order petal-shaped superimposed LG mode, and finally to the no-mode output; wherein the single-ring high-order petal-shaped superimposed LG mode is the required mode.

[0049] The above is only a specific embodiment of the present application, but the design concept of the present application is not limited to this, and any non-essential modification of the present application using this concept should be considered as an infringement of the protection scope of the present application.

Claims

1. A device for generating high-order superposition state (LG) modes, characterized in that, The pump light source, the first plano-convex lens, the conical lens, the second plano-convex lens and the laser resonant cavity are sequentially arranged. The pump light source generates horizontal pump laser and outputs to the first plano-convex lens. The first plano-convex lens collimates and focuses the pump laser on the conical lens. The conical lens generates a Bessel ring-shaped light beam and outputs to the second plano-convex lens. The second plano-convex lens focuses the Bessel ring-shaped light beam into the laser gain medium. The laser resonant cavity is composed of the laser gain medium, the third plano-convex lens and the plane mirror, the front end of the laser gain medium is coated as an input coupling mirror, and the plane mirror is coated as an output coupling mirror; wherein the Bessel ring-shaped light beam entering the laser resonant cavity excites the laser gain medium to generate a ring-shaped vortex light beam, the ring-shaped vortex light beam passes through the third plano-convex lens, and the ring-shaped vortex light beam satisfying the oscillation condition oscillates back and forth in the laser resonant cavity to generate a high-order superposition state LG mode, which is output through the output coupling mirror. Further comprising: a first multi-dimensional displacement table and a second multi-dimensional displacement table; the conical lens is fixedly connected with the first multi-dimensional displacement table, and the third plano-convex lens is fixedly connected with the second multi-dimensional displacement table; the first multi-dimensional displacement table moves along the laser propagation axis, or moves horizontally or up and down along the plane perpendicular to the laser propagation axis; the second multi-dimensional displacement table moves along the laser propagation axis, or moves horizontally or up and down along the plane perpendicular to the laser propagation axis.

2. The high-order superposition-state LG mode generating apparatus according to claim 1, wherein The pump light source is a single-mode fiber laser or a single-mode fiber-coupled semiconductor laser; the output wavelength of the pump light source matches the absorption wavelength of the laser gain medium, and the wavelength of the pump light source is between 400-2100 nm; the average output power of the pump light source is between 0-400 W.

3. The high-order superposition-state LG mode generating apparatus according to claim 1, wherein The distance between the first plano-convex lens and the light source output end face of the pump light source is the focal length of the first plano-convex lens.

4. The high-order superposition-state LG mode generating apparatus according to claim 1, wherein The conical lens is a circular conical prism.

5. The high-order superposition-state LG mode generating apparatus according to claim 1, wherein The substrate of the laser gain medium includes tungstate KGW, potassium lanthanum barium sodium fluoride KBLAN, yttrium vanadate YVO4, yttrium aluminum garnet YAG, yttrium lithium fluoride YLF, yttrium aluminate YAP or glass GLASS; wherein the yttrium vanadate YVO4, yttrium aluminum garnet YAG, yttrium lithium fluoride YLF, yttrium aluminate YAP or glass GLASS is doped with rare earth ions with a concentration of 0.2-10%; the length of the laser gain medium along the light propagation direction is between 2-15 mm.

6. The high-order superposition-state LG mode generating apparatus according to claim 1, wherein The focal length of the third plano-convex lens is between 10-40 mm.

7. The high-order superposition-state LG mode generating apparatus according to claim 1, wherein The laser resonant cavity is a plane-parallel cavity; the coated front end of the laser gain medium is the end of the laser gain medium facing the pump light source, and the coating of the front end of the laser gain medium is a dichroic film layer; the coating of the plane mirror is a single film layer; the distance between the input coupling mirror and the output coupling mirror is greater than the focal length of the third plano-convex lens by 10-20 mm.

8. The high-order superposition-state LG mode generating apparatus according to claim 1, wherein The wavelength of the ring-shaped vortex light beam generated by the laser gain medium is between 800 nm-2100 nm.

9. A method of generating a high-order superposition state LG mode based on the high-order superposition state LG mode generating apparatus according to any one of claims 1 to 8, characterized by, The method comprises the following steps: S1, coaxially arrange the pump light source, the first plano-convex lens, the conical lens, the second plano-convex lens, the laser gain medium and the plane mirror according to the direction of the generated laser; the convex surfaces of the first plano-convex lens and the second plano-convex lens both face the pump light source; the conical surface of the conical lens faces away from the pump light source; S2, generate pump laser by the pump light source, adjust the position of the first plano-convex lens to collimate the pump laser to the conical lens, the pump laser passes through the conical lens to generate a Bessel ring-shaped beam, the Bessel ring-shaped beam is focused by the second plano-convex lens to enter the laser gain medium, adjust the angle of the laser gain medium and the plane mirror to make the end face of the laser gain medium and the mirror face of the plane mirror perpendicular to the axis of the pump laser propagation, so that the laser mode generated by the pump laser exciting the gain medium oscillates multiple times in the laser resonant cavity to obtain laser output; S3, first roughly adjust the first multi-dimensional displacement table to change the position of the conical lens, so that the Bessel ring-shaped beam is focused at the coated front end face of the laser gain medium, then precisely adjust the first multi-dimensional displacement table to change the position of the conical lens, so that the center hole position of the focused Bessel ring-shaped beam is at the center of the coated front end face of the laser gain medium, and the Bessel ring-shaped beam excites the laser gain medium to generate a ring-shaped vortex beam; S4, insert the third plano-convex lens into the position close to the plane mirror in the laser resonant cavity by using the second multi-dimensional displacement table, the convex surface of the third plano-convex lens faces the pump light source, and the center of the third plano-convex lens is on the axis of the pump laser propagation, so that the ring-shaped vortex beam passes through the third plano-convex lens, and the ring-shaped vortex light that meets the oscillation condition oscillates multiple times in the laser resonant cavity; S5, precisely adjust the second multi-dimensional displacement table to slowly move the third plano-convex lens along the axis of the pump laser propagation to the direction of the laser gain medium, during the movement, based on the spherical aberration effect of the third plano-convex lens, the output mode is converted from the fundamental Gaussian beam to the multi-ring petal-shaped superimposed LG mode, then to the single-ring high-order petal-shaped superimposed LG mode, and finally to the no-mode output; wherein, the single-ring high-order petal-shaped superimposed LG mode is the required mode.

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