Device and method for directly generating vortex laser in cavity based on spiral phase plate

Abstract

The present invention relates to a device and method for directly generating a vortex laser in a cavity based on a spiral phase plate, belonging to the field of lasers. The device comprises a sequentially arranged pump source, a pump light coupling mirror, and a laser resonant cavity. The pump light coupling mirror comprises a first convex lens and a second convex lens, and the laser resonant cavity comprises an input coupling mirror, a gain medium, a third convex lens, and an output coupling mirror, which are sequentially arranged. The output coupling mirror directly utilizes a spiral phase plate, whose optical thickness is proportional to the azimuthal rotation and whose surface exhibits a spiral staircase structure. By adjusting the laser, the device can output a high-purity LG mode vortex laser. The device has a simpler and more direct structure and offers higher output power and improved mode purity.

Description

Technical Field

[0001] The present invention relates to a device and method for directly generating vortex laser in a cavity based on a spiral phase plate, belonging to the field of laser technology. Background Art

[0002] Vortex light is a light beam with a central phase singularity and a hollow, ring-shaped light field distribution. Its phase or wavefront is spiral, and its cylindrical coordinate expression contains the spiral phase phase exp(ilφ), where l is the topological core number. Currently, there are three main methods for generating vortex light: wavefront conversion using external phase modulation elements, nonlinear frequency conversion, and direct intracavity oscillation. A spiral phase plate is a phase modulation element commonly used for external modulation or direct intracavity oscillation to generate vortex light. External modulation involves inserting a spiral phase plate after the resonant cavity of an already generated laser, that is, after the output coupling mirror, to generate vortex laser light. Direct intracavity oscillation involves inserting a spiral phase plate into the resonant cavity, typically between the laser crystal and the output coupling mirror, to perform intracavity modulation. Currently, those skilled in the art believe that spiral phase plates are generally highly transparent to laser light, and using them directly as output coupling mirrors results in excessive intracavity losses, making direct laser generation difficult. Existing devices that use spiral phase plates to generate vortex light are relatively complex, low-power, and low-purity. Summary of the Invention

[0003] In response to the shortcomings of the existing technology, a device and method for directly generating vortex laser in a cavity based on a spiral phase plate are provided. By directly using the spiral phase plate as an output coupling mirror, high-purity and high-power vortex laser can be directly generated without passing through other optical modulation elements to generate vortex laser. The device has a simple structure and good effect.

[0004] To achieve the above technical objectives, a laser that directly generates vortex laser in a cavity based on a spiral phase plate includes a pump source, a pump light coupling mirror and a laser resonant cavity arranged in sequence, wherein the pump light coupling mirror includes a first convex lens and a second convex lens arranged in sequence, and the laser resonant cavity includes an input coupling mirror, a gain medium, a third convex lens and an output coupling mirror arranged in sequence; wherein the output coupling mirror directly adopts a spiral phase plate, the optical thickness of the spiral phase plate is proportional to the rotation of the azimuth angle, and the surface presents a spiral step structure. By adjusting the laser, it can output high-purity LG mode vortex laser.

[0005] Furthermore, the gain medium is a single crystal optical fiber, which is a laser crystal.

[0006] Furthermore, a 940 nm semiconductor laser is used as a pump source. The laser generated by the pump source is connected to a pump light coupling mirror via a coupling optical fiber. The diameter of the coupling optical fiber is 105 μm and the numerical aperture is 0.22.

[0007] Furthermore, the focal length of the first convex lens is 25.4 mm, and the focal length of the second convex lens is 75 mm. The first convex lens collimates the pump light, and the second convex lens focuses the pump light sent by the pump source and sends it directly to the laser resonant cavity.

[0008] Furthermore, the input coupling mirror is a plane mirror, and the surface of the resonant cavity input mirror is coated with a first dielectric film with a transmittance of >90% for a wavelength of 940nm and a reflectivity of >99.9% for a wavelength of 1030nm; the gain medium is a yttrium aluminum garnet crystal Yb:YAG single crystal fiber, the single crystal fiber has a diameter of 1mm, a length of 40mm, a Yb doping concentration of 1%, and the front and back surfaces of the single crystal fiber are coated with a second dielectric film with a transmittance of >99% for wavelengths of 940nm and 1030nm; the third convex lens 33 has a focal length of 175mm.

[0009] Furthermore, the output coupling mirrors formed by the spiral phase plate adopt the LG01 mode and the LG08 mode respectively. According to the required vortex laser mode, the output coupling mirrors of the corresponding mode can be directly replaced. When arranged, they are placed on the same axis as other lenses and located behind the third convex lens.

[0010] A method for directly generating vortex laser in a cavity based on a spiral phase plate, the steps of which are as follows:

[0011] Adjust the first convex lens to collimate the pump light sent by the pump source, adjust the position of the second convex lens and the gain medium to focus the pump light inside the gain medium, increase the output power of the pump source, and adjust the cavity mirror to generate a vortex laser. Place a CCD camera behind the output coupling mirror to monitor the spot pattern of the vortex laser output by the output coupling mirror. Adjust the position of the output coupling mirror until a uniform and complete annular spot pattern is displayed on the CCD camera, indicating that the laser is now outputting a vortex beam in the Laguerre Gaussian (LG) mode.

[0012] Furthermore, a Mach-Zehnder interferometer is placed in the direction of the laser output to detect the interference pattern of the vortex beam. Based on the monitored interference pattern and the topological core number characteristics of the vortex laser, the size of the topological core number can be directly obtained.

[0013] Beneficial Effects: The present invention utilizes single-crystal fiber as the gain medium. Compared to conventional optical fibers and bulk crystals, single-crystal fiber combines the advantages of conventional optical fibers (high surface-to-volume ratio and optical waveguide conversion efficiency) with the excellent physical and chemical properties of bulk crystals (high thermal conductivity, high laser damage threshold, and minimal nonlinear effects). This makes single-crystal fiber promising higher-power output and higher-energy laser transmission. The present invention directly utilizes single-crystal fiber as the gain medium and a spiral phase plate as the output mirror to produce high-purity, high-power vortex laser light.

[0014] This device uses a spiral phase plate as the output mirror. Depending on the order of the spiral phase plate, it can directly generate high-purity, high-energy vortex lasers in different Laguerre-Gaussian modes. At a pump power of 150W, it can produce a high-power LG01 mode laser output of 63W. Furthermore, compared with methods that use external modulation and direct intracavity insertion of a spiral phase plate to generate vortex lasers, this device is simpler and more direct, and offers higher output power and improved mode purity. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Schematic diagram of the structure of a device for directly generating vortex laser in a cavity based on a spiral phase plate according to an embodiment of the present invention.

[0016] Figure 2 This is a microscopic structure diagram of the output coupling mirror, i.e., the spiral phase plate, according to an embodiment of the present invention, wherein the left side is the LG01 mode and the right side is the LG08 mode.

[0017] Figure 3 The laser spots and interference patterns obtained in the embodiments of the present invention are the LG01 mode spot and interference pattern and the LG08 mode spot and interference pattern.

[0018] Figure 4 Graphs showing the output power and absorbed pump power of spiral phase plates using the LG01 and LG08 modes, respectively, according to an embodiment of the present invention.

[0019] In the figure: 1-pump source, 2-pump light coupling mirror, 3-laser resonant cavity, 21-first convex lens, 22-second convex lens, 31-input coupling mirror, 32-gain medium, 33-third convex lens, 34-output coupling mirror. DETAILED DESCRIPTION

[0020] The embodiments of the present invention are further described below with reference to the accompanying drawings:

[0021] like Figure 1 As shown, a device for directly generating vortex laser in a cavity based on a spiral phase plate comprises the following:

[0022] 1) Build a laser structure, including a pump source 1, a pump light coupling mirror 2 and a laser resonant cavity 3, wherein the pump light coupling mirror 2 is composed of a first convex lens 21 and a second convex lens 22, and the laser resonant cavity 3 is composed of an input coupling mirror 31, a gain medium 32, a third convex lens 33 and an output coupling mirror 34.

[0023] The pump source 1 is used to provide pump laser;

[0024] The pump light coupling mirror 2 is used to focus the laser light generated by the pump source 1 onto the input coupling mirror 31;

[0025] The resonant cavity input mirror 31 is used to receive the focused pump beam from the pump light coupling mirror 2 and output it to the gain medium 32;

[0026] The gain medium 32 is a single crystal optical fiber, which is a laser crystal;

[0027] The third convex lens 33 is used to lengthen the resonant cavity and expand the laser beam;

[0028] The output coupling mirror 34 is used to generate high-purity LG mode vortex laser output.

[0029] The pump source 1 is a 940 nm semiconductor laser. The laser light generated by the pump source is output through a coupling optical fiber. The diameter of the coupling optical fiber is 105 μm and the numerical aperture is 0.22.

[0030] The pump light coupling mirror 2 is composed of a first convex lens 21 and a second convex lens 22. The focal length of the first convex lens 21 is 25.4 mm and the focal length of the second convex lens 22 is 75 mm. The first convex lens 21 collimates the pump light, and the second convex lens 22 focuses the pump light.

[0031] The input coupling mirror 31 is a plane mirror, and the surface of the resonant cavity input mirror is coated with a first dielectric film with a transmittance greater than 90% for a wavelength of 940 nm and a reflectivity greater than 99.9% for a wavelength of 1030 nm.

[0032] The gain medium 32 is a Yb:YAG single crystal fiber doped with yttrium aluminum garnet crystal. The single crystal fiber has a diameter of 1 mm, a length of 40 mm, a Yb doping concentration of 1%, and a second dielectric film with a transmittance of >99% at wavelengths of 940 nm and 1030 nm on the front and back surfaces of the single crystal fiber.

[0033] Wherein, the third convex lens 33 has a focal length of 175 mm.

[0034] The output mirror 34 is a spiral phase plate, the optical thickness of which is proportional to the rotation of the azimuth angle, and the surface thereof presents a spiral step structure.

[0035] The spiral phase plate adopts LG01 mode and LG08 mode respectively. Figure 2 shown.

[0036] Wherein, the length of the laser resonant cavity is 255 mm.

[0037] 2) Adjust the first convex lens 21 to collimate the pump light so that the pump light spot size changes little when the pump light reaches the position of the second convex lens 22. Adjust the positions of the second convex lens 22 and the gain medium 32 so that the pump light is focused inside the gain medium 32. Adjust the laser so that its output laser power is large. Place a CCD camera behind the output coupling mirror 34 to monitor the output laser spot pattern. Adjust the position of the output coupling mirror 34 so that its center is aligned with the center of the output laser beam until a ring spot pattern is displayed on the CCD camera. The laser then outputs a vortex beam in the Laguerre-Gaussian mode. The generated vortex beam spot pattern is as shown in FIG. Figure 3 .

[0038] 3) Place a Mach-Zehnder interferometer in the direction of laser output to detect the interference pattern of the laser beam. The obtained interference pattern is as follows: Figure 3 From the clear interference pattern, it can be seen that the device generates vortex lasers of different modes and the purity of the generated vortex lasers is very high.

[0039] 4) Figure 4 The figure shows the output power and absorbed pump power of vortex lasers of different modes generated by using different output coupling mirrors. As shown in the figure, at an absorbed pump power of 130W, an LG01 mode laser with a power of up to 63W is generated, and the laser slope efficiency is 65%; at the same absorbed pump power, an LG08 mode laser output of 22W is generated, with a corresponding slope efficiency of 28%, and no obvious saturation is observed with the increase of absorbed pump power.

[0040] In summary, this device for directly generating vortex lasers within a cavity uses a spiral phase plate as an output coupling mirror. Depending on the order of the spiral phase plate, it can directly generate high-purity, high-power vortex lasers in different Laguerre-Gaussian modes. At a pump power of 150W, it can achieve a high-power LG01 mode laser output of 63W. Unlike other methods for generating vortex lasers, the experimental setup of this invention is simpler, and the vortex lasers produced are of higher purity and power.

Claims

1. A laser that directly generates vortex laser in a cavity based on a spiral phase plate, which is characterized by comprising a pump source (1), a pump light coupling mirror (2) and a laser resonant cavity (3) arranged in sequence, wherein the pump light coupling mirror (2) comprises a first convex lens (21) and a second convex lens (22) arranged in sequence, and the laser resonant cavity (3) comprises an input coupling mirror (31), a gain medium (32), a third convex lens (33) and an output coupling mirror (34) arranged in sequence; wherein the output coupling mirror (34) directly adopts a spiral phase plate, the optical thickness of the spiral phase plate is proportional to the rotation of the azimuth angle, and the surface presents a spiral step structure, and the laser can be adjusted to output high-purity LG mode vortex laser.

2. The laser for directly generating vortex laser in a cavity based on a spiral phase plate according to claim 1 is characterized in that the gain medium (32) is a single crystal optical fiber, which is a laser crystal.

3. The laser for directly generating vortex laser in a cavity based on a spiral phase plate according to claim 1 is characterized in that: the pump source (1) adopts a 940nm semiconductor laser, and the laser generated by the pump source (1) is connected to the pump light coupling mirror (2) through a coupling optical fiber, and the diameter of the coupling optical fiber is 105μm and the numerical aperture is 0.

22.

4. The laser for directly generating vortex laser in a cavity based on a spiral phase plate according to claim 1 is characterized in that: the focal length of the first convex lens (21) is 25.4 mm, the focal length of the second convex lens (22) is 75 mm, the first convex lens (21) collimates the pump light, and the second convex lens (22) focuses the pump light sent by the pump source (1) and sends the pipeline directly to the laser resonant cavity (3).

5. The laser for directly generating vortex laser in a cavity based on a spiral phase plate according to claim 1 is characterized in that: the input coupling mirror (31) is a plane mirror, and the surface of the resonant cavity input mirror is coated with a first dielectric film with a transmittance of >90% for a wavelength of 940nm and a reflectivity of >99.9% for a wavelength of 1030nm; the gain medium (32) is an ytterbium-doped yttrium aluminum garnet crystal Yb:YAG single crystal fiber, the single crystal fiber has a diameter of 1mm, a length of 40mm, a Yb doping concentration of 1%, and the front and rear surfaces of the single crystal fiber are coated with a second dielectric film with a transmittance of >99% for wavelengths of 940nm and 1030nm; the third convex lens 33 has a focal length of 175mm.

6. According to the laser for directly generating vortex laser in the cavity based on the spiral phase plate in claim 1, the characteristics are that: the output coupling mirror (34) composed of the spiral phase plate adopts the LG01 mode and the LG08 mode respectively. According to the required vortex laser mode, the output coupling mirror (34) of the corresponding mode can be directly replaced. When arranged, it is placed on the same axis as other lenses and is located after the third convex lens (33).

7. A method for directly generating vortex laser in a cavity based on a spiral phase plate, characterized in that Here are the steps: The first convex lens (21) is adjusted to collimate the pump light sent from the pump source (1), the positions of the second convex lens (22) and the gain medium (32) are adjusted to focus the pump light inside the gain medium (32), thereby increasing the output power of the pump source (1), and the cavity mirror is adjusted to generate a vortex laser. A CCD camera is placed relatively behind the output coupling mirror (34) to monitor the spot pattern of the vortex laser output by the output coupling mirror (34), and the position of the output coupling mirror (34) is adjusted until a ring spot pattern with uniform intensity and completeness is displayed on the CCD camera, indicating that the laser outputs a vortex beam in the Laguerre-Gaussian (LG) mode.

8. The method for directly generating vortex laser in a cavity based on a spiral phase plate according to claim 7, characterized in that: A Mach-Zehnder interferometer is placed in the laser output direction to detect the interference pattern of the vortex beam. The size of the topological nucleus number is directly obtained based on the monitored interference pattern and the topological nucleus number characteristics of the vortex laser.

Images