CN114784606A - Laguerre Gaussian beam generating device and method - Google Patents

Abstract

The invention relates to a Laguerre Gaussian beam generating device and method, and belongs to the field of lasers. The laser polarization beam splitter comprises a pumping laser, a collimating lens, a focusing lens, a concave dichroic mirror, a concave reflecting mirror highly reflecting laser, a plane laser reflecting mirror, a polarizing plate, an 1/4 wave plate, a laser crystal and a polarization beam splitter; the laser crystal is a uniaxial crystal, the laser crystal is used as a gain medium to generate laser, the spin angular momentum of partial circularly polarized light is converted into orbital angular momentum, the 1/4 wave plate is used for converting the polarization state of the light between circularly polarized light and linearly polarized light, and the polarization beam splitter mirror is used for outputting vortex rotation with the topological kernel number of 2; the partial laser passes through another 1/4 wave plate and a polarization beam splitter, and the output forms vortex laser. Another portion of the laser continues to oscillate within the laser cavity providing energy for conversion to eddy rotation. The vortex laser has no interference of other modes, has high power and high efficiency, is not limited by wavelength, and can generate high-purity vortex laser.

Description

Laguerre Gaussian beam generating device and method

technical field

The invention relates to a Laguerre Gaussian beam generating device and method, belonging to the field of lasers.

Background technique

The generation and application of Laguerre Gaussian beam is one of the research hotspots worldwide in recent years. The wavefront of the beam is helical and there is a phase singularity in the center. Therefore, the central light intensity of the Laguerre Gaussian beam is 0. Gaussian beams carry orbital angular momentum, so they are also called OAM beams (orbital angular momentum, OAM). The Laguerre Gaussian beam plays a very important role in many fields. It can realize the non-contact capture of particles in the biological field, directly measure the angular velocity of the rotating body in the measurement field, and realize a new information encoding method in the field of optical communication. .

At present, the methods of directly generating Laguerre Gaussian beams in the cavity include the extra-cavity method and the intra-cavity direct generation method. The so-called extra-cavity conversion method is relatively simple, but it is easily affected by optical devices, so the conversion efficiency, power and purity of the Laguerre Gaussian beam are also low;

Intracavity mode generation is to use a laser crystal to directly generate a Laguerre Gaussian beam in the cavity. The methods mainly include the direct insertion of the phase element into the resonant cavity method and the non-planar rotating optical path technology. The former is limited by the inserted optical device, while the latter is only for Single wavelength and low damage threshold. There are also some new methods for the direct oscillation generation method in the cavity. The first one is the ring pump method, which modulates the spot of the pump light into a ring, and realizes the direct oscillation output of the vortex laser through the mode matching of the pump light and the oscillating laser. 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 is too troublesome and has poor mode control. The problem of not being able to recycle is serious. The second is ring doping, which changes the traditional core doping into a ring doping layer, such as a ring-doped fiber and a laser containing the fiber proposed by Huazhong University of Science and Technology, although the laser oscillation is practical. The above is carried out in a ring waveguide, but the placement of each cladding and the control of the refractive index are still cumbersome. The third method is to recover the pump light leaked from the laser cavity, such as the ring pump laser proposed by the Institute of Optoelectronics of the Chinese Academy of Sciences. Although it is equipped with a pump light recovery device, it has higher requirements on the size and placement of the pump focusing mirror. Still not efficient enough and susceptible to interference from other modes.

SUMMARY OF THE INVENTION

In view of the shortcomings of the prior art, a device and method for generating a Laguerre-Gaussian beam that uses a uniaxial laser crystal as a gain medium to convert spin angular momentum to orbital angular momentum based on an intra-cavity direct oscillation method are provided. The structure is simple, the use is convenient, and the laser is continuously converted between linearly polarized light and circularly polarized light.

In order to achieve the above technical purpose, 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 reflecting mirror a arranged on a horizontal axis. , in which a laser crystal a is arranged 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 horizontally inclined at a 3°-10° angle between the concave dichroic mirror a and the concave mirror a; the concave dichroic mirror A resonant cavity is arranged on the light path of a, and the resonant cavity includes a 1/4 wave plate b, a polarizer and a plane mirror b arranged in sequence, and a 1/4 wave plate a, a polarizing mirror a and a The beam splitter mirror a and the plane mirror a; the laser crystal a is excited by the pump laser generated by the pump laser a to generate a laser with a wavelength of 790nm-808nm through the resonator oscillation, so that the circularly polarized light and the linearly polarized light are not separated. Stop the conversion, and then use the polarizing beam splitter mirror a for screening, so that it can periodically generate vortex light. Under the screening of the vertical polarizer, the laser light entering the laser crystal a is a left-handed circularly polarized laser.

The focusing lens a is a plano-convex mirror with a focal length of 7.5cm and a transmittance greater than 95%, both sides are coated with a high-transmittance film corresponding to the central wavelength of the pump light, and the collimating lens a is coated with a corresponding pump light on both sides. High-transmittance film with central wavelength, plano-convex mirror with focal length of 15cm and transmittance greater than 95%; concave dichroic mirror a is coated with a film with high transparency for pump light on the front facing the pump source, and on the back reverse membrane.

The laser crystal a can not only generate laser light but also is a uniaxial crystal, including tetragonal, trigonal and hexagonal crystals are optical uniaxial crystals, and the uniaxial laser crystal is used as the gain medium, so that the spin angle Momentum is converted into orbital angular momentum; the doping ions of laser crystal a are one of rare earth ions such as Nd ³⁺ , Yb ³⁺ , Er ³⁺ , Tm ³⁺ , Ho ³⁺ , and the left and right ends are plated with corresponding The anti-reflection coating of the pump light center wavelength and the corresponding laser center wavelength; the laser crystal a is Nd:YVO4, and the left and right ends are coated with the corresponding pump light center wavelength and the corresponding laser center wavelength, and the transmittance is greater than 95% antireflection coating.

The pump laser a is a semiconductor laser or fiber laser with a wavelength of 800 nm, the center wavelength of the pump laser a is λ ₀ =800 nm, the fiber laser pigtail core diameter is 100 μm, and the semiconductor laser has a numerical aperture NA=0.22.

A working method of a Laguerre Gaussian beam generating device. The 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 to the concave mirror a. The generated laser light consists of two parts, one is left-handed circularly polarized light, the other Part of the vortex light with right-handed topological nucleus number 2 is reflected by the left concave mirror a to the 1/4 wave plate a, and the left-handed circularly polarized light of the laser entering the 1/4 wave plate a is converted into a vertical direction The polarized linearly polarized light, and the right-handed vortex light is converted into a horizontally polarized vortex beam; the horizontally polarized vortex light and the vertically polarized linearly polarized light are completely divided into two beams of light after passing through the polarizing beam splitter mirror, The vortex light is separated by the polarizing beam splitter mirror a and output, while the vertically polarized light beam goes back and forth in the same way through the plane mirror a, and is converted into a relatively right-handed circularly polarized light after passing through the 1/4 wave plate a. After being reflected by the concave mirror a, it is injected into the laser crystal a again to generate the same right-handed circularly polarized light and left-handed vortex light in the opposite direction, followed by the pump laser a through the collimating lens a and the new pump generated by the focusing lens a. The laser beam is converted into vertically polarized linearly polarized light and horizontally polarized vortex light respectively through the 1/4 wave plate b of the resonator. After that, the two parts of light continue to pass through the polarizer to eliminate the horizontally polarized vortex light, leaving The linearly polarized light polarized in the vertical direction is reflected by the plane mirror b to the concave dichroic mirror a, and after being reflected by the concave dichroic mirror a4, it is still the linearly polarized light polarized in the vertical direction, and the previous steps are continued.

A Laguerre Gaussian beam generating device, comprising a pump laser b, a collimating lens b, a focusing lens, a concave dichroic mirror b, a laser crystal b and a concave reflecting mirror b arranged on a horizontal axis, the concave dichroic mirror b and a concave surface The horizontal inclination angle between the mirror b and the laser crystal b is 3°-10°. The reflected light path of the concave dichroic mirror b is successively arranged on the same axis with a horizontal angle of 5° linear polarizer and plane reflection. There are 1/4 wave plate c and concave mirror c on the reflected light path of mirror d and concave mirror b. The 1/4 wave plate c and concave mirror c are inclined at 5° to the incident direction of the pump light, and the concave reflection A polarized light crystal and a concave mirror d are successively arranged on the reflection pipeline of mirror c, and a 1/4 wave plate arranged on the same axis and at an included angle of 5° with the horizontal direction is successively arranged on the reflected light path of the concave mirror d. d, Polarizing beam splitter mirror b, and flat mirror c.

A beam generating method of a Laguerre Gaussian beam generating device, the steps of which are:

After the pump laser b generates the pump light, it can be used to couple out the pump light through the fiber coupling unit, and then the collimation lens b and the focusing lens b are used to collimate and focus the pump light respectively;

After the collimation and focusing are completed, the pump light is successively sent to the laser crystal b through the concave dichroic mirror b, and up-converted fluorescence is generated under the excitation of the pump light, and the up-converted fluorescence is reflected to the polarizer through the concave dichroic mirror b. Under the selection of the chip, the laser center wavelength of the laser crystal b is 1532nm, which is reflected to the concave dichroic mirror b through the plane mirror d, and then enters the laser crystal b after being reflected by the concave dichroic mirror b. At this time, the laser of the laser crystal b only contains vertical Directionally polarized laser;

The vertically polarized laser light of the laser crystal b is reflected by the concave mirror b and enters the 1/4 wave plate c to generate left-handed circularly polarized light. Left-handed circularly polarized light, while the other part is right-handed vortex light with a topological kernel number of 2;

The two parts of the laser light generated by the crystals with two different polarizations are reflected by the left concave mirror d, and then enter the 1/4 wave plate d. The vortex light is converted into a horizontally polarized vortex light;

The horizontally polarized vortex light and the vertically polarized linearly polarized light are completely divided into vortex beams and vertically polarized beams after passing through the polarization beam splitter mirror b. The vortex beams are separated by the polarization beam splitter mirror b and output, while the vertical The polarized light beam is reflected by the sending plane mirror and continues to go back and forth. After passing through the 1/4 wave plate d, it is converted into a circularly polarized light that is reversely viewed in the right direction. After being reflected by the concave mirror d, it enters the uniaxial crystal again to generate a reverse Look at the same right-handed circularly polarized light and left-handed vortex light;

Looking in the opposite direction, the same right-handed circularly polarized light and left-handed vortex light are reflected by the concave mirror c, and then converted into vertically polarized linearly polarized light and horizontally polarized vortex light after passing through the 1/4 wave plate c, respectively. After the polarized linearly polarized light and the vortex light polarized in the horizontal direction continue to generate laser light through the laser crystal b, the vortex light polarized in the horizontal direction is eliminated by the linear polarizer, leaving the linearly polarized light polarized in the vertical direction, and the concave dichroic mirror b After the reflection, it is still the linearly polarized light polarized in the vertical direction, and the previous steps are continued.

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

The focusing lens is a plano-convex lens with a 1532nm high transmission film on both sides and a focal length of 2.5cm, and the collimating lens b is a plano-convex lens with a 1532nm high transmission film on both sides and a focal length of 10cm.

Beneficial effect: By setting the polarizer and the 1/4 wave plate, the pump laser is continuously converted between circularly polarized light and linearly polarized light, and then the vertical polarizer is used for screening, so that it can periodically generate vortex light the resonant cavity. The intra-cavity direct oscillation method is realized to generate a higher-purity Laguerre Gaussian beam, which solves the problems of difficult optical device fabrication process, high fabrication cost, and difficulty in beam generation when the Laguerre Gaussian beam is generated. The structure is simple, the realization cost is low, there is no interference of other modes, the power is high, the efficiency is high, and it is not limited by the wavelength, and can generate a high-purity vortex laser.

Description of drawings

1 is a schematic structural diagram of Embodiment 1 of the Laguerre Gaussian beam generating device of the present invention;

Fig. 2 is the schematic diagram of the vortex light intensity distribution density of right-handed in the present invention;

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

4 is a schematic structural diagram of Embodiment 2 of the Laguerre Gaussian beam generating device of the present invention;

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, 7-1/4 wave plate a, 8-polarization beam splitter mirror a, 9-plane mirror a, 10-1/4 wave plate b, 11-polarizer, 12-plane mirror b, 13-pump laser b, 14-collimation Lens b, 15-focusing lens b, 16-concave dichroic mirror b, 17-laser crystal b, 18-concave mirror b, 19-1/4 wave plate c, 20-concave mirror c, 21-polarized light crystal , 22-concave mirror d, 23-1/4 wave plate d, 24-polarization beam splitter mirror b, 25-plane mirror c, 26-linear polarizer, 27-plane mirror d.

Detailed ways

Embodiments of the present invention will be further described below in conjunction with the accompanying drawings:

Example 1: Using a crystal to generate a Laguerre Gaussian beam;

As shown in Figure 1, a new Laguerre Gaussian beam generating device is characterized in that the device includes the following steps:

It includes 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 polarizing beam splitter mirror a8 arranged in sequence; the resonator includes a line for generating linearly polarized light Polarizing plate 11, 1/4 wave plate c7 and 1/4 wave plate 10, flat mirror c12, and concave mirror a6 for reflecting laser light and changing the direction of the optical path.

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

The fiber coupling unit is used to couple out the pump light generated by the pump source, and the pump laser is a semiconductor laser or a fiber laser with a wavelength of 800 nm.

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

The collimating lens is used for collimating the pump light, and the focusing lens is used for focusing the pump light. A concave mirror is a concave mirror. The focusing lens is a plano-convex lens with a focal length of 7.5cm, both sides are coated with 800nm high transmittance film with transmittance greater than 95%, and the collimating lens is coated on both sides with 800nm and transmittance greater than 95% Plano-convex mirror with high transmission film and focal length of 15cm; the reflective lens is coated with a film highly reflective to pump light. The laser crystal is Nd:YVO4 with a doping concentration of 1.22 at.%, and both the left and right end surfaces are plated with an anti-reflection film with a transmittance of more than 95% for 800nm and 1064nm;

The new Laguerre Gaussian beam generating device is further explained through the embodiment: first, the pump laser a1, the collimating lens a2, the focusing lens a3, the concave dichroic mirror a4, the laser crystal a5, and the concave mirror a6 are arranged on the horizontal axis; 1/4 wave plate 7, polarizing beam splitter mirror a8, plane mirror 9 are arranged on the same axis, and the included angle with the horizontal direction is 5°; 1/4 wave plate 10, vertical polarizer 11, plane mirror 12 They are arranged on the same axis, and the included angle with the horizontal direction is also 5°. The pump laser a1 can be selected as a semiconductor laser to generate pump light with a wavelength of 800nm, preferably, the pump laser a1 is a semiconductor laser with a center wavelength of λ ₀ =800nm and a fiber core diameter of 100um and NA = 0.22;

When the pump light is generated, it can be used to couple out the pump light through the fiber coupling unit, and then the collimating lens a2 and the focusing lens a3 are used to collimate and focus the pump light respectively, and in order to make the collimation and The focusing effect is better. The focusing lens a3 is a plano-convex lens with a focal length of 7.5cm and is coated with 800nm on both sides and has a transmittance greater than 95%. The collimating lens a2 is coated on both sides with 800nm and transmittance greater than 95% high transmission film, plano-convex lens with focal length of 15cm;

After the collimation and focusing are completed, the pump light passes through the concave dichroic mirror a4, and the laser crystal a5 oscillates through the resonator under the excitation of the pump light to generate laser light with a wavelength of 790nm-808nm. The laser entering the laser crystal a5 is a left-handed circularly polarized laser. Further, the laser generated after entering the crystal contains two parts, one is the same left-handed circularly polarized light, as shown in Figure 3, and the other is a right-handed topology The vortex light with a nucleus number of 2, after being reflected by the left concave mirror a6, enters the 1/4 wave plate 7, and further, the left-handed circularly polarized light is converted into vertically polarized linearly polarized light, while the right-handed vortex The rotatory light is transformed into a horizontally polarized vortex light, and the right-handed vortex light is shown in Figure 2;

The horizontally polarized vortex light and the vertically polarized linearly polarized light pass through the polarizing beam splitter mirror 7 and are completely divided into two beams of light, the vortex light is output, and the vertically polarized light beam is reflected by the plane mirror 8 and continues to go back and forth. The 1/4 wave plate 7 is converted into a relatively right-handed circularly polarized light. After being reflected by the concave mirror a6, it is injected into the laser crystal a5 again to generate the same right-handed circularly polarized light and left-handed vortex light in the opposite direction;

Further, 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 after passing through the 1/4 wave plate 10. The polarized vortex light is eliminated, leaving linearly polarized light polarized in the vertical direction, which is still linearly polarized in the vertical direction after being reflected by the concave dichroic mirror a4, and the previous steps are continued.

The fiber coupling unit is used to couple out the pump light generated by the pump source, and the pump laser is a semiconductor laser or a fiber laser whose center wavelength is the corresponding absorption peak of the crystal. The crystal must be capable of not only generating laser light but also being a uniaxial crystal. The tetragonal, trigonal and hexagonal crystals are all optical uniaxial crystals. The uniaxial laser crystal is used as the gain medium to convert the spin angular momentum into orbital angular momentum. The formula used in the principle is as follows:

in:

其中λ为波长，w₀为光束半径，n₀与n_e为晶体o光与e光的折射率。

Where λ is the wavelength, w ₀ is the beam radius, n ₀ and _ne are the refractive indices of crystal o light and e light.

where E is the electric field constant, Ein is the input electric field, and Eout is the output electric field;

Example 2: Using two crystals to generate a Laguerre Gaussian beam

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

As shown in Figure 4, to generate a cavity for the second Laguerre Gaussian beam, the device includes the following steps:

It includes pump laser a13, collimating lens 14, focusing lens 15, concave dichroic mirror 16, laser crystal b17, concave mirror b18, polarizing beam splitter mirror b24, linear polarizer 26, 1/4 wave plate c19, 1/4 wave plate d23, plane mirror c25, plane mirror d27, polarized light crystal 21, concave mirror c20 and concave mirror d22.

The concave mirror b18 is placed at an angle of 5° 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 transparent to the pump light, and the reverse side is coated with a high reflectivity to the laser. film.

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

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

The collimating lens is used for collimating the pump light, and the focusing lens is used for focusing the pump light. A concave mirror is a concave mirror. The focusing lens is a plano-convex lens with a focal length of 2.5cm and a high-transmittance film of 1532nm and a transmittance greater than 95% on both sides. A plano-convex mirror with a high transmission film and a focal length of 10cm; the reflective lens is coated with a film that is highly reflective to pump light. The laser crystal is Er:YAG with a doping concentration of 0.5at.%, and the end faces are all coated with an antireflection film with a transmittance greater than 95% for 1532nm and 1064nm;

The new Laguerre Gaussian beam generating device is further explained through an embodiment: first, the pump laser a13, the collimating lens 14, the focusing lens 15, the concave dichroic mirror 16, the laser crystal 17, and the concave mirror b18 are arranged on the horizontal axis; The 1/4 wave plate c19 and the concave mirror c20 are inclined at 5° to the incident direction of the pump light, and the polarizing beam splitter mirror b24, the plane mirror 25 and the 1/4 wave plate d23 are arranged on the same axis, and are arranged on the same axis as the horizontal direction. The included angle is 5°; 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 the included angle with the horizontal direction is also 5° . The pump laser a13 can be selected as a semiconductor laser to generate pump light with a wavelength of 1532nm, preferably, the pump laser a13 is a semiconductor laser with a center wavelength of λ ₀ =1532nm and a fiber core diameter of 200um and NA=0.1;

After the pump light is generated, it can be used to couple out the pump light through the fiber coupling unit, and then the collimation lens 14 and the focusing lens 15 are used to collimate and focus the pump light respectively. The focusing effect is better. The focusing lens 15 is a plano-convex lens with a 1532nm high transmission film on both sides and a focal length of 2.5cm. The collimating lens 14 is a plano-convex mirror with a 1532nm high transmission film on both sides and a focal length of 10cm. ;

After the collimation and focusing are completed, the pump light passes through the concave dichroic mirror 16, the laser crystal 17 generates up-converted fluorescence under the excitation of the pump light, and the laser with the center wavelength of 1532 nm is generated by the resonator oscillation. Under the selection of plate 26, the laser light entering the laser crystal 17 only contains laser light polarized in the vertical direction, and further, the 1/4 wave plate c19 generates left-handed circularly polarized light, and further, the left-handed circularly polarized light is incident on the uniaxial The laser generated after the crystal 21 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 nucleus number of 2. After being reflected by the left concave mirror d22, it enters 1/4 of the light. Wave plate d23, the left-handed circularly polarized light is converted into vertically polarized linearly polarized light, and the right-handed vortex light is converted into horizontally polarized vortex light;

The horizontally polarized vortex light and the vertically polarized linearly polarized light are completely divided into two beams of light after passing through the polarizing beam splitter mirror b24, the vortex light is output, and the vertically polarized light beam is reflected by the plane mirror 25 and continues to go back and forth. The 1/4 wave plate d23 is converted into circularly polarized light that looks right-handed in the opposite direction. After being reflected by the concave mirror d22, it enters the uniaxial crystal 21 again to generate circularly-polarized light that looks opposite to the right-handed and left-handed vortex light. ;

After the two parts of the light are reflected by the concave mirror c20, they are transformed into the vertically polarized linearly polarized light and the horizontally polarized vortex light respectively through the 1/4 wave plate c19. 26, the vortex light polarized in the horizontal direction is eliminated, leaving the linearly polarized light polarized in the vertical direction, which is still the linearly polarized light polarized in the vertical direction after being reflected by the concave dichroic mirror 16, and the previous steps are continued.

Claims (9)

1. A Laguerre Gaussian beam generating device is characterized in that: the laser device comprises a pump laser a (1), a collimating lens a (2), a focusing lens a (3), a concave dichroic mirror a (4) and a concave reflecting mirror a (6) which are arranged on a horizontal axis, wherein a laser crystal a (5) is arranged between the concave dichroic mirror a (4) and the concave reflecting mirror a (6), and the concave surfaces of the concave dichroic mirror a (4) and the concave reflecting mirror a (6) and the laser crystal a (5) form an inclination angle of 3-10 degrees horizontally; a resonant cavity is arranged on the light path of the concave dichroic mirror a (4), the resonant cavity comprises 1/4 wave plate b (10), a polarizing plate (11) and a plane mirror b (12) which are sequentially arranged, and a 1/4 wave plate a (7), a polarization beam splitter mirror a (8) and a plane mirror a (9) are sequentially arranged on the pipeline path of the concave mirror a (6); the laser crystal a (5) is excited by pump laser generated by a pump laser a (1) to generate laser with the wavelength of 790nm-808nm through resonant cavity oscillation, so that circularly polarized light and linearly polarized light are converted continuously, then a polarization beam splitter a (8) is used for screening to enable the circularly polarized light and the linearly polarized light to become vortex-generated optical rotation periodically, and the laser entering the laser crystal a (5) is levorotatory circularly polarized laser under the screening of a vertical polarizing plate (11).

2. The apparatus for generating a laguerre gaussian beam according to claim 1, wherein: the focusing lens a (3) is a plano-convex lens with two surfaces plated with high-transmittance films corresponding to the central wavelength of the pump light and a focal length of 7.5cm and a transmittance of more than 95%, and the collimating lens a (2) is a plano-convex lens with two surfaces plated with high-transmittance films corresponding to the central wavelength of the pump light and a focal length of 15cm and a transmittance of more than 95%; the front surface of the concave dichroic mirror a (4) facing the pumping source is plated with a film which is highly transparent to pumping light, and the back surface is plated with a film which is highly reflective to laser.

3. The laguerre gaussian beam generation apparatus according to claim 1, wherein: the laser crystal a (5) can generate laser and is a uniaxial crystal, crystals including a tetragonal system, a trigonal system and a hexagonal system are all optical uniaxial crystals, and the uniaxial laser crystal is used as a gain medium, so that the spin angular momentum is converted to the orbital angular momentum; the doping ion of the laser crystal a (5) is Nd³⁺、Yb³⁺、Er³⁺、Tm³⁺、Ho³⁺One of the rare earth ions is plated with antireflection films corresponding to the central wavelength of the pump light and the central wavelength of the laser light on the left end face and the right end face; the laser crystal a (5) is Nd, YVO4, and the left and right end faces are both plated with antireflection films with transmittance of more than 95% corresponding to the central wavelength of the pump light and the central wavelength of the laser light.

4. The laguerre gaussian beam generation apparatus according to claim 1, wherein: the pump laser a (1) is a semiconductor laser or a fiber laser which generates a laser with the wavelength of 800nm, and the central wavelength of the pump laser a (1) is lambda₀800nm, the tail fiber core diameter of the fiber laser is 100um, and the numerical aperture NA of the semiconductor laser is 0.22.

5. A method of operating the laguerre gaussian beam generating apparatus of claim 1, comprising the steps of: the pump laser emitted by a pump laser a (1) is collimated by a collimating lens a (2), then the pump light is focused by a focusing lens a (3), the focused pump light enters a laser crystal a (5) through a concave dichroic mirror a (4), the pump laser entering the laser crystal a (5) enables the laser crystal a (5) to generate laser light to emit to a concave reflector a (6), the generated laser light comprises two parts, one part is left-handed circularly polarized light, the other part is right-handed vortex optical rotation with the topological kernel number of 2, after the generated laser light is reflected to 1/4 wave plate a (7) by a left concave reflector a (6), the left-handed circularly polarized light of the laser entering 1/4 wave plate a (7) is converted into linearly polarized light in the vertical direction, and the right-handed vortex optical rotation is converted into vortex light polarized in the horizontal direction; vortex light polarized in the horizontal direction and linearly polarized light polarized in the vertical direction are completely divided into two beams of light after passing through a polarization beam splitter mirror (7), the vortex light is separated by a polarization beam splitter mirror a (8) and then output, the vertically polarized light beam continues to reciprocate in the original path through a plane reflector a (9), the vertically polarized light beam is converted into circularly polarized light which is relatively right-handed through a 1/4 wave plate a (7), the circularly polarized light is reflected by a concave reflector a (6) and then enters a laser crystal a (5) again to generate vortex optical rotation which is the same as the circularly polarized light on the right hand and the vortex optical rotation on the left hand and is reversely seen, a pumping laser beam which is newly generated by a following pump laser a (1) through a collimating lens a (2) and a focusing lens a (3) is converted into linearly polarized light polarized in the vertical direction and vortex optical rotation polarized in the horizontal direction through a 1/4 wave plate b (10) of a resonant cavity respectively, and then the vortex optical rotation on the two parts of light continues to eliminate the vortex light polarized in the horizontal direction after passing through a polarizing plate (11), the linearly polarized light polarized in the vertical direction is left to be reflected to the concave dichroic mirror a (4) by the plane reflecting mirror b (12), and is still the linearly polarized light polarized in the vertical direction after being reflected by the concave dichroic mirror a4, and the previous steps are repeated.

6. A Laguerre Gaussian beam generating device is characterized in that: comprises a pump laser b (13), a collimating lens b (14), a focusing lens (15), a concave dichroic mirror b (16), a laser crystal b (17) and a concave reflecting mirror b (18) which are arranged on a horizontal axis, wherein the concave dichroic mirror b (16), the concave reflecting mirror b (18) and the laser crystal b (17) are horizontally inclined at an angle of 3-10 degrees, a linear polarizer (26) and a plane reflecting mirror d (27) which are arranged on the same axis and have an included angle of 5 degrees in the horizontal direction are sequentially arranged on a reflecting light path of the concave dichroic mirror b (16), 1/4 wave plate c (19) and a concave reflecting mirror c (20) are sequentially arranged on the reflecting light path of the concave reflecting mirror b (18), the 1/4 wave plate c (19) and the concave reflecting mirror c (20) are inclined at an angle of 5 degrees with the incident direction of pump light, a polarizing crystal (21) and a concave reflecting mirror d (22) are sequentially arranged on the reflecting light path of the concave reflecting mirror c (20), 1/4 wave plate d (23), polarization beam splitter mirror b (24) and plane reflector c (25) which are arranged on the same axis and have an included angle of 5 degrees with the horizontal direction are sequentially arranged on the reflection light path of the concave reflector d (22).

7. A light beam generating method using the laguerre gaussian light beam generating apparatus of claim 6, comprising the steps of:

after the pump laser b (13) generates pump light, the pump light can be coupled out through the optical fiber coupling unit, and then the pump light is respectively collimated and focused through the collimating lens b (14) and the focusing lens b (15) in sequence;

after collimation and focusing are finished, pumping light is sent to a laser crystal b (17) through a concave surface dichroic mirror b (16) in sequence and generates up-conversion fluorescence under the excitation of the pumping light, the up-conversion fluorescence is reflected to a polarizing plate (26) through the concave surface dichroic mirror b (16), under the selection of the polarizing plate (26), the central wavelength of the laser passing through the laser crystal b (17) is 1532nm, the laser is reflected to the concave surface dichroic mirror b (16) through a plane reflecting mirror d (27), the laser enters the laser crystal b (17) after being reflected by the concave surface dichroic mirror b (16), and at the moment, the laser of the laser crystal b (17) only contains the laser polarized in the vertical direction;

the laser polarized in the vertical direction of the laser crystal b (17) is reflected by a concave reflector b (18) and enters 1/4 wave plate c (19) to generate left-handed circularly polarized light, and the laser generated after the circular circularly polarized light enters a polarized light crystal (21) comprises two parts, wherein one part is the same left-handed circularly polarized light, and the other part is right-handed vortex rotation with the topological nucleus number of 2;

two parts of laser generated by crystals (21) of two different polarized lights are reflected by a left concave reflecting mirror d (22) and then enter 1/4 wave plate d (23), wherein, left-handed circularly polarized light is converted into linearly polarized light polarized in the vertical direction, and right-handed vortex optical rotation is converted into vortex light polarized in the horizontal direction;

vortex light polarized in the horizontal direction and linearly polarized light polarized in the vertical direction are completely divided into vortex light beams and vertically polarized light beams after passing through a polarization beam splitter mirror b (24), the vortex light beams are separated by the polarization beam splitter mirror b (24) and then output, the vertically polarized light beams continue to reciprocate after being reflected by a sending plane reflector (25), are converted into circularly polarized light which is viewed rightwards in the reverse direction through an 1/4 wave plate d (23), and are reflected by a concave surface reflector d (22) and then enter a uniaxial crystal (21) again to generate circularly polarized light which is viewed rightwards in the reverse direction and vortex optical rotation which is viewed leftwards in the reverse direction;

after the same right-handed circularly polarized light and the same left-handed vortex light are reflected by the concave reflecting mirror c (20) in the opposite view, the same right-handed circularly polarized light and the same left-handed vortex light are respectively converted into linearly polarized light in the vertical direction and vortex light in the horizontal direction through the 1/4 wave plate c (19), after the linearly polarized light in the vertical direction and the vortex light in the horizontal direction continuously generate laser through the laser crystal b (17), the linearly polarized light in the horizontal direction is eliminated through the polarizing plate (26), the linearly polarized light in the vertical direction is remained, the linearly polarized light in the vertical direction is still obtained after the linearly polarized light in the vertical direction is reflected by the concave dichroic mirror b (16), and the previous steps are continuously repeated.

8. The method for generating a light beam by using a laguerre gaussian light beam generating apparatus according to claim 7, wherein: the pump laser b (13) is a semiconductor laser for generating pump light with wavelength of 1532nm and center wavelength of λ₀The core diameter of the optical fiber is 1532nm and the NA is 0.1 um.

9. The beam generating method of the laguerre gaussian beam generating apparatus as claimed in claim 7, wherein: the focusing lens (15) is a plano-convex lens with two sides coated with 1532nm high-transmittance films and a focal length of 2.5cm, and the collimating lens b (14) is a plano-convex lens with two sides coated with 1532nm high-transmittance films and a focal length of 10 cm.

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