Laguerre-Gaussian beam generating apparatus and method

Abstract

The present invention relates to a Laguerre-Gaussian beam generating device and method, belonging to the field of lasers. It includes a pump laser, a collimating lens, a focusing lens, a concave dichroic mirror, a concave mirror with high reflectivity for laser, a plane laser mirror, a polarizer, a quarter-wave plate, a laser crystal and a polarization beam splitter; wherein the laser crystal is a uniaxial crystal, the laser crystal is used as a gain medium to generate laser, and at the same time, the spin angular momentum of part of the circularly polarized light is converted into orbital angular momentum. The quarter-wave plate is used to convert the polarization state of light between circularly polarized light and linearly polarized light, and the polarization beam splitter is used to output vortex light with a topological charge number of 2; this part of the laser passes through another quarter-wave plate and a polarization beam splitter to output and form vortex laser. Another part of the laser continues to oscillate in the laser cavity to provide the energy for conversion into vortex light. It has no interference from other modes, and has high power and high efficiency, is not limited by the wavelength, and can generate high-purity vortex laser.

Description

Technical Field

[0001] The present invention relates to a Laguerre-Gaussian beam generating device and method, belonging to the field of lasers. Background Art

[0002] The generation and application of Laguerre-Gaussian beams have been one of the research hotspots worldwide in recent years. The wavefront of this beam is spiral-shaped and there is a phase singularity at the center. Therefore, the central light intensity of the Laguerre-Gaussian beam is 0. Since the Laguerre-Gaussian beam carries orbital angular momentum, it is also called an OAM beam (orbital angular momentum, OAM). Laguerre-Gaussian beams play a very important role in many fields. In the biological field, it can achieve non-contact capture of microparticles. In the measurement field, it can directly measure the angular velocity of a rotating body. And in the field of optical communication, it can achieve a new information coding method.

[0003] At the present stage, the methods for directly generating Laguerre-Gaussian beams in the cavity include the external cavity method and the in-cavity direct generation method. The so-called external cavity conversion method is relatively simple, but it is easily affected by optical devices. Therefore, the conversion efficiency and power of the Laguerre-Gaussian beam are relatively low, and the purity is poor.

[0004] The in-cavity mode generation means directly generating Laguerre-Gaussian beams in the cavity using a laser crystal. The main methods include directly inserting a phase element into the resonant cavity method and the non-planar rotating optical path technology. The former is limited by the inserted optical devices, while the latter is only applicable to a single wavelength and has a low damage threshold. There are also some new methods for the in-cavity direct oscillation generation method. The first is the ring pumping method, which modulates the pump light spot into a ring shape, and realizes the direct oscillation output of the vortex laser through the mode matching between the pump light and the oscillating laser. However, the modulation process of the pump light will inevitably lead to the complexity of the entire laser device, and making the pump light into a ring shape is too troublesome and the mode controllability is poor. For example, when performing mode matching through a ring-shaped pump light spot, the problem of serious leakage of the pump light that cannot be recovered from the laser cavity is serious. The second is the ring doping, which changes the traditional core doping into a ring doping layer. For example, a ring doping layer optical fiber and a laser including the optical fiber proposed by Huazhong University of Science and Technology. Although the laser oscillation actually occurs in a ring waveguide, the placement of each cladding layer and the control of the refractive index are still relatively cumbersome. The third is to recover the pump light leaked from the laser cavity. For example, the ring pumping laser proposed by the Institute of Optoelectronics, Chinese Academy of Sciences. Although it is equipped with a pump light recovery device, it has high requirements for the size and placement position of the pump focusing mirror, and the efficiency is still not high enough and it is easily interfered by other modes. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, a Laguerre-Gaussian beam generating device and method for converting spin angular momentum into orbital angular momentum based on the intracavity direct oscillation method using a uniaxial laser crystal as the gain medium are provided. The structure is simple and convenient to use, and continuously converts the laser between linearly polarized light and circularly polarized light.

[0006] To achieve the above technical objectives, a Laguerre-Gaussian beam generating device of the present invention includes a pump laser a, a collimating lens a, a focusing lens a, a concave dichroic mirror a, and a concave mirror a arranged on a horizontal axis. A laser crystal a is provided between the concave dichroic mirror a and the concave mirror a, and the concave surfaces of the concave dichroic mirror a and the concave mirror a are both inclined at an angle of 3° - 10° horizontally with respect to the laser crystal a; a resonant cavity is provided on the optical path of the concave dichroic mirror a, and the resonant cavity includes a quarter-wave plate b, a polarizer, and a plane mirror b arranged in sequence. A quarter-wave plate a, a polarization beam splitter mirror a, and a plane mirror a are arranged in sequence on the optical path of the concave mirror a; the laser crystal a is excited by the pump laser generated by the pump laser a and oscillates through the resonant cavity to generate a laser with a wavelength of 790nm - 808nm, enabling the continuous conversion between circularly polarized light and linearly polarized light. Then, the polarization beam splitter mirror a is used for screening to make it periodically generate vortex light. Under the screening of the vertical polarizer, the laser incident on the laser crystal a is left-handed circularly polarized laser.

[0007] The focusing lens a is a plano-convex lens with both sides coated with a high-transmission film corresponding to the central wavelength of the pump light, a focal length of 7.5 cm, and a transmittance greater than 95%. The collimating lens a is a plano-convex lens with both sides coated with a high-transmission film corresponding to the central wavelength of the pump light, a focal length of 15 cm, and a transmittance greater than 95%. The front surface of the concave dichroic mirror a facing the pump source is coated with a film with high transmittance for the pump light, and the back surface is coated with a film with high reflectivity for the laser.

[0008] The laser crystal a can not only generate laser but also is a uniaxial crystal. Crystals including tetragonal, trigonal, and hexagonal crystal systems are all optical uniaxial crystals. Using a uniaxial laser crystal as the gain medium enables the conversion of spin angular momentum into orbital angular momentum; the doped ions of the laser crystal a are one of rare earth ions such as Nd 3+ 、Yb 3+ 、Er 3+ 、Tm 3+ 、Ho 3+ etc., and both left and right end faces are coated with an antireflection film corresponding to the central wavelength of the pump light and the central wavelength of the corresponding laser; the laser crystal a is specifically Nd:YVO4, and both left and right end faces are coated with an antireflection film corresponding to the central wavelength of the pump light and the central wavelength of the corresponding laser with a transmittance greater than 95%.

[0009] The pump laser a is a semiconductor laser or a fiber laser that generates a wavelength of 800 nm, and the central wavelength of the pump laser a is λ 0 = 800 nm. The core diameter of the pigtail of the fiber laser is 100 um, and the numerical aperture NA of the semiconductor laser is 0.22.

[0010] A working method of a Laguerre-Gaussian beam generating device, the steps of which are as follows: The pump laser emitted by the pump laser a is collimated by the collimating lens a, and then the pump light is focused by the focusing lens a. The focused pump light enters the laser crystal a through the concave dichroic mirror a. The pump laser entering the laser crystal a causes the laser crystal a to generate laser light and emit it towards the concave mirror a. The generated laser light contains two parts, one part is left-handed circularly polarized light, and the other part is right-handed vortex light with a topological charge of 2. After being reflected by the left concave mirror a towards the quarter-wave plate a, the left-handed circularly polarized light in the laser light entering the quarter-wave plate a is converted into linearly polarized light polarized in the vertical direction, while the right-handed vortex light is converted into a vortex beam polarized in the horizontal direction; the vortex light polarized in the horizontal direction and the linearly polarized light polarized in the vertical direction are completely split into two beams of light after passing through the polarization beam splitter mirror. The vortex light is separated by the polarization beam splitter mirror a and output, while the vertically polarized beam continues to travel back and forth along the original path through the plane mirror a, is converted into relatively right-handed circularly polarized light after passing through the quarter-wave plate a, and after being reflected by the concave mirror a, is again incident on the laser crystal a to generate right-handed circularly polarized light and left-handed vortex light that also look right-handed when viewed in the reverse direction. Following the pump laser a, the newly generated pump laser beam passes through the collimating lens a and the focusing lens a and is respectively converted into linearly polarized light polarized in the vertical direction and vortex light polarized in the horizontal direction by the quarter-wave plate b of the resonator. Then, the two parts of light continue to pass through the polarizer to eliminate the vortex light polarized in the horizontal direction, leaving the linearly polarized light polarized in the vertical direction to be reflected by the plane mirror b towards the concave dichroic mirror a. After being reflected by the concave dichroic mirror a4, it is still linearly polarized light polarized in the vertical direction, and the previous steps are continued.

[0011] A Laguerre-Gaussian beam generating device includes a pump laser b, a collimating lens b, a focusing lens, a concave dichroic mirror b, a laser crystal b, and a concave mirror b arranged on the horizontal axis. The concave dichroic mirror b and the concave mirror b are inclined at an angle of 3° - 10° horizontally with respect to the laser crystal b. On the reflection light path of the concave dichroic mirror b, a linear polarizer with a horizontal included angle of 5° and a plane mirror d arranged on the same axis are successively provided. On the reflection light path of the concave mirror b, a quarter-wave plate c and a concave mirror c are successively provided. The quarter-wave plate c and the concave mirror c are inclined at an angle of 5° with respect to the pump light incident direction. On the reflection light path of the concave mirror c, a uniaxial crystal and a concave mirror d are successively provided. On the reflection light path of the concave mirror d, a quarter-wave plate d, a polarization beam splitter mirror b, and a plane mirror c arranged on the same axis and with an included angle of 5° with respect to the horizontal direction are successively provided.

[0012] A beam generation method for a Laguerre-Gaussian beam generation device, the steps of which are as follows:

[0013] After the pump laser b generates pump light, it can first pass through the fiber coupling unit to couple and output the pump light, and then successively pass through the collimating lens b and the focusing lens b to collimate and focus the pump light respectively;

[0014] When the collimation and focusing are completed, the pump light passes through the concave dichroic mirror b and is sent to the laser crystal b, and up-conversion fluorescence is generated under the excitation of the pump light. The up-conversion fluorescence is reflected by the concave dichroic mirror b to the polarizer. Under the selection of the polarizer, the laser center wavelength of the laser crystal b is 1532 nm, which is reflected by the plane mirror d to the concave dichroic mirror b, and then reflected by the concave dichroic mirror b and enters the laser crystal b. At this time, the laser of the laser crystal b only contains the laser polarized in the vertical direction;

[0015] The laser polarized in the vertical direction of the laser crystal b is reflected by the concave mirror b and enters the quarter-wave plate c to generate left-handed circularly polarized light. The laser generated after the left-handed circularly polarized light enters the uniaxial crystal contains two parts. One part is the same left-handed circularly polarized light, and the other part is the right-handed vortex light with a topological charge of 2;

[0016] The two parts of the laser generated by the crystals of the two different polarized lights are reflected by the left concave mirror d and then enter the quarter-wave plate d. Among them, the left-handed circularly polarized light is converted into linearly polarized light polarized in the vertical direction, and the right-handed vortex light is converted into vortex light polarized in the horizontal direction;

[0017] The vortex light polarized in the horizontal direction and the linearly polarized light polarized in the vertical direction are completely separated into a vortex beam and a vertically polarized beam after passing through the polarization beam splitter mirror b. The vortex beam is separated by the polarization beam splitter mirror b and output, while the vertically polarized beam is reflected by the transmitting plane mirror and continues to travel back and forth. After passing through the quarter-wave plate d, it is converted into right-handed circularly polarized light when viewed in the reverse direction. After being reflected by the concave mirror d, it enters the uniaxial crystal again to generate right-handed circularly polarized light and left-handed vortex light that are the same when viewed in the reverse direction;

[0018] The right-handed circularly polarized light and the left-handed vortex light that are the same when viewed in the reverse direction are reflected by the concave mirror c and then are respectively converted into linearly polarized light polarized in the vertical direction and vortex light polarized in the horizontal direction through the quarter-wave plate c. After the linearly polarized light polarized in the vertical direction and the vortex light polarized in the horizontal direction pass through the laser crystal b and continue to generate laser, the vortex light polarized in the horizontal direction is eliminated by the polarizer, leaving the linearly polarized light polarized in the vertical direction. After being reflected by the concave dichroic mirror b, it is still linearly polarized light polarized in the vertical direction, and the previous steps are continued.

[0019] The pump laser b is a semiconductor laser, which is used to generate pump light with a wavelength of 1532 nm, and the central wavelength is λ 0 = 1532 nm, the core diameter of the optical fiber is 200 um, and NA = 0.1.

[0020] The focusing lens is a plano-convex lens with both sides coated with a high-transmission film of 1532 nm and a focal length of 2.5 cm. The collimating lens b is a plano-convex lens with both sides coated with a high-transmission film of 1532 nm and a focal length of 10 cm.

[0021] Advantageous effects: By setting the polarizer and the quarter-wave plate, the pump laser continuously converts between circularly polarized light and linearly polarized light, and then uses a vertical polarizer for screening to make it a resonant cavity that can periodically generate vortex light. It realizes the generation of higher-purity Laguerre-Gaussian beams by the in-cavity direct oscillation method, solves the problems such as the difficult manufacturing process of optical devices, high manufacturing cost, and difficulty in generating beams when generating Laguerre-Gaussian beams. Its structure is simple, the implementation cost is low, there is no interference from other modes, the power is high, the efficiency is high, it is not limited by the wavelength, and it can generate high-purity vortex laser. Description of the Drawings

[0022] Figure 1 is a schematic structural diagram of Embodiment 1 of the Laguerre-Gaussian beam generating device of the present invention;

[0023] Figure 2 is a schematic diagram of the light intensity distribution density of the right-handed vortex light in the present invention;

[0024] Figure 3 is a schematic diagram of the light intensity distribution density of the left-handed circularly polarized light in the present invention;

[0025] Figure 4 is a schematic structural diagram of Embodiment 2 of the Laguerre-Gaussian beam generating device of the present invention;

[0026] In the figure: 1 - pump laser a, 2 - collimating lens a, 3 - focusing lens a, 4 - concave dichroic mirror a, 5 - laser crystal a, 6 - concave mirror a, 7 - quarter-wave plate a, 8 - polarization beam splitter mirror a, 9 - plane mirror a, 10 - quarter-wave plate b, 11 - polarizer, 12 - plane mirror b, 13 - pump laser b, 14 - collimating lens b, 15 - focusing lens b, 16 - concave dichroic mirror b, 17 - laser crystal b, 18 - concave mirror b, 19 - quarter-wave plate c, 20 - concave mirror c, 21 - uniaxial crystal, 22 - concave mirror d, 23 - quarter-wave plate d, 24 - polarization beam splitter mirror b, 25 - plane mirror c, 26 - linear polarizer, 27 - plane mirror d. Detailed Embodiments

[0027] The following further describes the embodiments of the present invention with reference to the drawings:

[0028] Example 1: Using a crystal to generate Laguerre-Gaussian beams;

[0029] As Figure 1 shown, a new device for generating Laguerre-Gaussian beams is characterized in that the device comprises the following steps:

[0030] Including a pump laser a1, a collimating lens a2, a focusing lens a3, a concave dichroic mirror a4, a laser crystal a5, a concave mirror a6 and a polarization beam splitter mirror a8 arranged in sequence; The resonant cavity includes a linear polarizer 11 for generating linearly polarized light, a quarter-wave plate c7 and a quarter-wave plate 10, a plane mirror c12, and a concave mirror a6 for reflecting the laser and changing the optical path direction.

[0031] The concave mirror a6 is placed at an angle of 5° with respect to the incident direction of the pump light. The side of the concave dichroic mirror a(4) facing the pump source is coated with a film highly transparent to the pump light, and the reverse side is coated with a film highly reflective to the laser.

[0032] The fiber coupling unit is used to couple and output the pump light generated by the pump source, and the pump laser is a semiconductor laser or a fiber laser generating a wavelength of 800 nm.

[0033] The pump laser has a central wavelength of λ 0 = 800 nm, the core diameter of the semiconductor laser pigtail is 100 um, and the numerical aperture NA of the semiconductor laser is 0.22.

[0034] The collimating lens is used to collimate the pump light, and the focusing lens is used to focus the pump light. The concave mirror is a concave mirror. The focusing lens is a plano-convex lens with both sides coated with a highly transparent film of 800 nm and a transmittance greater than 95% and a focal length of 7.5 cm. The collimating lens is a plano-convex lens with both sides coated with a highly transparent film of 800 nm and a transmittance greater than 95% and a focal length of 15 cm; The reflecting lens is coated with a film highly reflective to the pump light. The laser crystal is Nd:YVO4 with a doping concentration of 1.22 at.%, and both left and right end faces are coated with an antireflection film with a transmittance greater than 95% for 800 nm and 1064 nm;

[0035] The new Laguerre-Gaussian beam generating device is further described through embodiments: First, the pump laser a1, collimating lens a2, focusing lens a3, concave dichroic mirror a4, laser crystal a5, and concave mirror a6 are arranged on the horizontal axis; the quarter-wave plate 7, polarization beam splitter mirror a8, and plane mirror 9 are arranged on the same axis, with an angle of 5° with the horizontal direction; the quarter-wave plate 10, vertical polarizer 11, and plane mirror 12 are arranged on the same axis, also with an angle of 5° with the horizontal direction. The pump laser a1 can be a semiconductor laser, used to generate pump light with a wavelength of 800 nm. Preferably, the pump laser a1 is a semiconductor laser with a central wavelength of λ 0 = 800 nm, a fiber core diameter of 100 um, and a NA = 0.22;

[0036] After the pump light is generated, it can first pass through the fiber coupling unit to couple and output the pump light, and then pass through the collimating lens a2 and focusing lens a3 in sequence to collimate and focus the pump light respectively. And to make the collimation and focusing effects better, the focusing lens a3 is a plano-convex lens with both sides coated with a high-transmission film of 800 nm and a transmittance greater than 95%, and a focal length of 7.5 cm. The collimating lens a2 is a plano-convex lens with both sides coated with a high-transmission film of 800 nm and a transmittance greater than 95%, and a focal length of 15 cm;

[0037] After collimation and focusing are completed, the pump light passes through the concave dichroic mirror a4. The laser crystal a5 oscillates through the resonant cavity under the excitation of the pump light to generate laser with a wavelength of 790 nm - 808 nm. Under the screening of the vertical polarizer 11, the laser incident on the laser crystal a5 is left-handed circularly polarized laser. Further, the laser generated after entering the crystal contains two parts. One part is the same left-handed circularly polarized light, as Figure 3 shown, and the other part is a right-handed vortex light with a topological charge of 2. After being reflected by the left concave mirror a6, it enters the quarter-wave plate 7. Further, the left-handed circularly polarized light is converted into linearly polarized light polarized in the vertical direction, while the right-handed vortex light is converted into vortex light polarized in the horizontal direction. The right-handed vortex light is as Figure 2 shown;

[0038] The vortex light polarized in the horizontal direction and the linearly polarized light polarized in the vertical direction are completely split into two beams of light after passing through the polarization beam splitter mirror a8. The vortex light is output, and the vertically polarized beam is reflected by the plane mirror b12 and continues to travel back and forth. After passing through the quarter-wave plate 7, it is converted into relatively right-handed circularly polarized light. After being reflected by the concave mirror a6, it enters the laser crystal a5 again to generate right-handed circularly polarized light and left-handed vortex light that is the same when viewed in the reverse direction;

[0039] Furthermore, after the two parts of light are reflected by the concave dichroic mirror a4, they are respectively converted into linearly polarized light polarized in the vertical direction and vortex light polarized in the horizontal direction through the quarter-wave plate 10. After the two parts of light pass through the polarizer 11, the vortex light polarized in the horizontal direction is eliminated, leaving the linearly polarized light polarized in the vertical direction, which remains linearly polarized light polarized in the vertical direction after being reflected by the concave dichroic mirror a4, and the previous steps are continued to be repeated.

[0040] The fiber coupling unit is used to couple and output the pump light generated by the pump source, and the pump laser is a semiconductor laser or a fiber laser that generates pump light with a central wavelength corresponding to the absorption peak of the crystal. The crystal must satisfy not only the ability to generate laser but also be a uniaxial crystal. Crystals of the tetragonal system, trigonal system, and hexagonal system are all optical uniaxial crystals. Using a uniaxial laser crystal as the gain medium enables the conversion of spin angular momentum to orbital angular momentum.

[0041] Embodiment 2: Generating Laguerre-Gaussian beams using two crystals

[0042] The present invention will be further described below with reference to the accompanying drawings.

[0043] As Figure 4 shown, it is the second type of Laguerre-Gaussian beam generation cavity type, and this device includes the following steps:

[0044] It successively includes a pump laser a13, a collimating lens 14, a focusing lens 15, a concave dichroic mirror 16, a laser crystal b17, a concave mirror b18, a polarization beam splitter mirror b24, a linear polarizer 26, a quarter-wave plate c19, a quarter-wave plate d23, a plane mirror c25, a plane mirror d27, a uniaxial crystal 21, a concave mirror c20, and a concave mirror d22.

[0045] The concave mirror b18 is placed at an inclination of 5° with respect to the incident direction of the pump light. The side of the concave dichroic mirror a(4) facing the pump source is coated with a film that is highly transmissive to the pump light, and the reverse side is coated with a film that is highly reflective to the laser.

[0046] The fiber coupling unit is used to couple and output the pump light generated by the pump source, and the pump laser is a semiconductor laser or a fiber laser that generates light with a wavelength of 1532 nm.

[0047] The pump laser has a central wavelength of λ 0 = 1532 nm, the core diameter of the semiconductor laser pigtail is 200 um, and the numerical aperture of the semiconductor laser is NA = 0.1.

[0048] The collimating lens is used to collimate the pump light, and the focusing lens is used to focus the pump light. The concave mirror is a concave mirror. The focusing lens is a plano-convex lens with both sides coated with a high-transmission film of 1532 nm and a transmittance greater than 95%, and a focal length of 2.5 cm. The collimating lens is a plano-convex lens with both sides coated with a high-transmission film of 1532 nm and a transmittance greater than 95%, and a focal length of 10 cm. The reflecting lens is coated with a film with high reflectivity for the pump light. The laser crystal is Er:YAG with a doping concentration of 0.5 at.%, and both end faces are coated with an antireflection film with a transmittance greater than 95% for 1532 nm and 1064 nm.

[0049] The new Laguerre-Gaussian beam generating device is further described by way of examples: First, the pump laser a13, the collimating lens 14, the focusing lens 15, the concave dichroic mirror 16, the laser crystal b17, and the concave mirror b18 are arranged on the horizontal axis. The quarter-wave plate c19 and the concave mirror c20 are inclined at 5° to the incident direction of the pump light. The polarization beam splitter mirror b24, the plane mirror c25, and the quarter-wave plate d23 are arranged on the same axis and are at an angle of 5° to the horizontal direction. The concave mirror c20, the concave mirror d22, and the uniaxial crystal 21 are arranged on the same axis. The polarizer 26 and the plane mirror 27 are arranged on the same axis and are also at an angle of 5° to the horizontal direction. The pump laser a13 can be a semiconductor laser, used to generate pump light with a wavelength of 1532 nm. Preferably, the pump laser a13 is a semiconductor laser with a central wavelength of λ 0 = 1532 nm, a fiber core diameter of 200 um, and NA = 0.1.

[0050] After the pump light is generated, it can first pass through the fiber coupling unit to couple and output the pump light, and then pass through the collimating lens 14 and the focusing lens 15 in sequence to collimate and focus the pump light respectively. And to make the collimation and focusing effects better, the focusing lens 15 is a plano-convex lens with both sides coated with a high-transmission film of 1532 nm and a focal length of 2.5 cm, and the collimating lens 14 is a plano-convex lens with both sides coated with a high-transmission film of 1532 nm and a focal length of 10 cm.

[0051] After collimation and focusing are completed, the pump light passes through the concave dichroic mirror 16. The laser crystal b17 generates up-conversion fluorescence under the excitation of the pump light and generates a laser with a central wavelength of 1532 nm through the oscillation of the resonant cavity. Further, under the selection of the polarizer 26, the laser incident on the laser crystal b17 only contains the laser polarized in the vertical direction. Further, the incident 1 / 4 wave plate c19 generates left-handed circularly polarized light. Further, the laser generated after the left-handed circularly polarized light is incident on the uniaxial crystal 21 contains two parts. One part is the left-handed circularly polarized light of the same handedness, and the other part is the right-handed vortex light with a topological charge of 2. After being reflected by the left concave mirror d22, it is incident on the 1 / 4 wave plate d23. The left-handed circularly polarized light is converted into linearly polarized light polarized in the vertical direction, and the right-handed vortex light is converted into vortex light polarized in the horizontal direction;

[0052] The vortex light polarized in the horizontal direction and the linearly polarized light polarized in the vertical direction are completely split into two beams of light after passing through the polarization beam splitter mirror b24. The vortex light is output, and the vertically polarized beam is reflected by the plane mirror c25 and continues to travel back and forth. After passing through the 1 / 4 wave plate d23, it is converted into right-handed circularly polarized light when viewed in the reverse direction. After being reflected by the concave mirror d22, it is incident on the uniaxial crystal 21 again to generate right-handed circularly polarized light of the same handedness and left-handed vortex light when viewed in the reverse direction;

[0053] After the two parts of light are reflected by the concave mirror c20, they are respectively converted into linearly polarized light polarized in the vertical direction and vortex light polarized in the horizontal direction through the 1 / 4 wave plate c19. After the two parts of light continue to generate laser through the laser crystal b17, the vortex light polarized in the horizontal direction is eliminated by the polarizer 26, leaving the linearly polarized light polarized in the vertical direction. After being reflected by the concave dichroic mirror 16, it is still linearly polarized light polarized in the vertical direction, and the previous steps are continued.

Claims

1. A Laguerre-Gaussian beam generating device, characterized in that: it includes a pump laser a (1), a collimating lens a (2), a focusing lens a (3), a concave dichroic mirror a (4) and a concave mirror a (6) arranged in sequence on a horizontal axis. A laser crystal a (5) is provided between the concave dichroic mirror a (4) and the concave mirror a (6). The concave surfaces of the concave dichroic mirror a (4) and the concave mirror a (6) are both inclined at an angle of 3° - 10° horizontally with respect to the laser crystal a (5); A resonant cavity is provided on the optical path of the concave dichroic mirror a (4). The resonant cavity includes a quarter-wave plate b (10), a polarizer (11) and a plane mirror b (12) arranged in sequence. On the optical path of the concave mirror a (6), a quarter-wave plate a (7), a polarization beam splitter mirror a (8) and a plane mirror a (9) are arranged in sequence; The laser crystal a (5) is excited by the pump laser generated by the pump laser a (1) and oscillates through the resonant cavity to generate laser with a wavelength of 790nm - 808nm, enabling the continuous conversion between circularly polarized light and linearly polarized light. Then, the polarization beam splitter mirror a (8) is used for screening to make it periodically generate vortex light. Under the screening of the vertical polarizer (11), the laser incident on the laser crystal a (5) is left-handed circularly polarized laser; The laser crystal a (5) can not only generate laser but also is a uniaxial crystal. Using a uniaxial laser crystal as the gain medium enables the conversion of spin angular momentum to orbital angular momentum.

2. The Laguerre-Gaussian beam generating device according to claim 1, characterized in that: The focusing lens a (3) is a plano-convex lens with both sides coated with a high-transmission film corresponding to the central wavelength of the pump light, a focal length of 7.5 cm, and a transmittance greater than 95%. The collimating lens a (2) is a plano-convex lens with both sides coated with a high-transmission film corresponding to the central wavelength of the pump light, a focal length of 15 cm, and a transmittance greater than 95%; The front side of the concave dichroic mirror a (4) facing the pump source is coated with a film highly transmissive to the pump light, and the back side is coated with a film highly reflective to the laser.

3. The Laguerre-Gaussian beam generating device according to claim 1, characterized in that: The laser crystal a (5) includes crystals of tetragonal system, trigonal system and hexagonal system, all of which are optically uniaxial crystals; the doped ions of the laser crystal a (5) are Nd 3+ , Yb 3+ , Er 3+ , Tm 3+ , Ho 3+ One of the rare earth ions, and antireflection films corresponding to the center wavelength of the pump light and the center wavelength of the corresponding laser are coated on both left and right end faces.

4. The Laguerre-Gaussian beam generating device according to claim 1, characterized in that: The pump laser a (1) is a semiconductor laser or a fiber laser that generates a wavelength of 800 nm, and the center wavelength of the pump laser a (1) is λ 0 = 800 nm. The core diameter of the pigtail of the fiber laser is 100 um, and the numerical aperture NA of the semiconductor laser is 0.

22.

5. A working method of the Laguerre-Gaussian beam generating device according to claim 1, characterized in that The steps are as follows: The pump laser emitted by the pump laser a (1) is collimated by the collimating lens a (2), and then the pump light is focused by the focusing lens a (3). The focused pump light enters the laser crystal a (5) through the concave dichroic mirror a (4). The pump laser entering the laser crystal a (5) causes the laser crystal a (5) to generate laser light and emit it towards the concave mirror a (6). The generated laser light consists of two parts, one part is left-handed circularly polarized light, and the other part is right-handed vortex light with a topological charge of 2. After being reflected by the left concave mirror a (6) towards the quarter-wave plate a (7), the left-handed circularly polarized light in the laser light entering the quarter-wave plate a (7) is converted into linearly polarized light polarized in the vertical direction, while the right-handed vortex light is converted into a vortex beam polarized in the horizontal direction; The vortex light polarized in the horizontal direction and the linearly polarized light polarized in the vertical direction are completely split into two beams of light after passing through the polarization beam splitter mirror (8). The vortex light is separated by the polarization beam splitter mirror a (8) and output, while the vertically polarized beam continues to travel back and forth along the original path through the plane mirror a (9), is converted into relatively right-handed circularly polarized light after passing through the quarter-wave plate a (7), and after being reflected by the concave mirror a (6), enters the laser crystal a (5) again to generate right-handed circularly polarized light and left-handed vortex light that is also right-handed when viewed in the reverse direction. Following the pump laser a (1) through the collimating lens a (2) and the focusing lens a (3), the newly generated pump laser beam in the resonator is converted into linearly polarized light polarized in the vertical direction and vortex light polarized in the horizontal direction through the quarter-wave plate b (10) of the resonator respectively. Then, after the two parts of light continue to pass through the polarizer (11), the vortex light polarized in the horizontal direction is eliminated, leaving the linearly polarized light polarized in the vertical direction to be reflected by the plane mirror b (12) towards the concave dichroic mirror a (4). After being reflected by the concave dichroic mirror a4, it is still linearly polarized light polarized in the vertical direction, and the previous steps are continued.

6. A Laguerre-Gaussian beam generating device, characterized in that: It includes a pump laser b (13), a collimating lens b (14), a focusing lens b (15), a concave dichroic mirror b (16), a laser crystal b (17), and a concave mirror b (18) arranged in sequence on a horizontal axis. There is an inclination angle of 3° - 10° horizontally between the concave dichroic mirror b (16) and the concave mirror b (18) and the laser crystal b (17). On the reflection optical path of the concave dichroic mirror b (16), a linear polarizer (26) with an included angle of 5° in the horizontal direction and a plane mirror d (27) are arranged in sequence on the same axis. On the reflection optical path of the concave mirror b (18), a quarter-wave plate c (19) and a concave mirror c (20) are arranged in sequence. The quarter-wave plate c (19) and the concave mirror c (20) are inclined at 5° to the pump light incident direction. On the reflection optical path of the concave mirror c (20), a uniaxial crystal (21) and a concave mirror d (22) are arranged in sequence. On the reflection optical path of the concave mirror d (22), a quarter-wave plate d (23) located on the same axis and inclined at 5° to the horizontal direction, a polarization beam splitter mirror b (24), and a plane mirror c (25) are arranged in sequence.

7. A beam generation method using the Laguerre-Gaussian beam generation device according to claim 6, characterized in that the steps are as follows: After the pump laser b (13) generates pump light, it can first pass through a fiber coupling unit to couple and output the pump light, and then the collimating lens b (14) and the focusing lens b (15) are used to collimate and focus the pump light in sequence; When collimation and focusing are completed, the pump light passes through the concave dichroic mirror b (16) and is sent to the laser crystal b (17), and up-conversion fluorescence is generated under the excitation of the pump light. The up-conversion fluorescence is reflected by the concave dichroic mirror b (16) to the polarizer (26). Under the selection of the polarizer (26), the central wavelength of the laser passing through the laser crystal b (17) is 1532 nm, and it is reflected by the plane mirror d (27) to the concave dichroic mirror b (16), and then reflected by the concave dichroic mirror b (16) and enters the laser crystal b (17). At this time, the laser of the laser crystal b (17) only contains laser polarized in the vertical direction; The laser polarized in the vertical direction of the laser crystal b (17) is reflected by the concave mirror b (18) and enters the quarter-wave plate c (19) to generate left-handed circularly polarized light. The circularly polarized light enters the uniaxial crystal (21) and the generated laser contains two parts. One part is the same left-handed circularly polarized light, and the other part is right-handed vortex light with a topological charge of 2; The two parts of the laser generated by the uniaxial crystal (21) with different polarizations are reflected by the left concave mirror d (22) and then enter the quarter-wave plate d (23). Among them, the left-handed circularly polarized light is converted into linearly polarized light polarized in the vertical direction, and the right-handed vortex light is converted into vortex light polarized in the horizontal direction; The horizontally polarized vortex light and the vertically polarized linearly polarized light are completely split into a vortex beam and a vertically polarized beam after passing through the polarization beam splitter mirror b (24). The vortex beam is output after being separated by the polarization beam splitter mirror b (24), while the vertically polarized beam is reflected by the plane mirror b (25) and continues to travel back and forth. After passing through the quarter-wave plate d (23), it is converted into a right-handed circularly polarized light when viewed in the reverse direction. After being reflected by the concave mirror d (22), it enters the uniaxial crystal (21) again and generates a right-handed circularly polarized light and a left-handed vortex light that are also right-handed when viewed in the reverse direction; The right-handed circularly polarized light and the left-handed vortex light that are also right-handed when viewed in the reverse direction are reflected by the concave mirror c (20), and then pass through the quarter-wave plate c (19) and are respectively converted into a vertically polarized linearly polarized light and a horizontally polarized vortex light. After the vertically polarized linearly polarized light and the horizontally polarized vortex light pass through the laser crystal b (17) and continue to generate laser, the horizontally polarized vortex light is eliminated by the polarizer (26), leaving the vertically polarized linearly polarized light. After being reflected by the concave dichroic mirror b (16), it remains a vertically polarized linearly polarized light and continues to repeat the previous steps.

8. The beam generation method of the Laguerre-Gaussian beam generation device according to claim 7, characterized in that: The pump laser b (13) is a semiconductor laser for generating pump light with a wavelength of 1532 nm, and the central wavelength is λ 0 = 1532 nm, the core diameter of the optical fiber is 200 um, and NA = 0.

1.

9. The beam generation method of the Laguerre-Gaussian beam generation device according to claim 7, characterized in that: The focusing lens b (15) is a plano-convex lens with both sides coated with a high-transmission film of 1532 nm and a focal length of 2.5 cm, and the collimating lens b (14) is a plano-convex lens with both sides coated with a high-transmission film of 1532 nm and a focal length of 10 cm.

Images