Off-axis pumping chiral controllable single-frequency vortex laser output device

Abstract

According to the off-axis pumping chiral controllable single-frequency vortex laser output device provided by the invention, the pumping coupling lens is promoted to deviate from the optical axis through the displacement module, so that the pumping light deviates from the optical axis and generates small-angle deviation, and chiral controllable single-frequency vortex laser output is realized by utilizing the characteristic that the vortex light chirality is sensitive to the incident angle of the pumping laser. The requirements of some specific scenes, such as the fields of composite coherent detection, laser communication and the like, can be met; the method for realizing the chiral controllable single-frequency vortex laser provided by the invention is simple, the structure is compact, the integration degree is high, and the output laser has the advantages of low noise, narrow line width, good stability and the like.

Description

Technical Field

[0001] The invention belongs to the field of laser technology, and in particular relates to a single-frequency chiral controllable vortex laser. Background Art

[0002] A vortex beam is a light field with a spiral phase and annular intensity distribution, with a phase singularity at its center, and all photons in the beam carry orbital angular momentum. This type of beam is widely used in many fields such as optical communications, quantum information, biological microscopy, and rotational Doppler detection.

[0003] The common output mode of lasers that directly generate vortex beams is multi-longitudinal mode, and there are relatively few reports on single-frequency vortex light lasers. Patent CN115579719A discloses a single-frequency vortex light laser, which uses an axicon to convert a Gaussian beam into a ring beam, and uses the ring beam to pump a single-block non-planar ring cavity to achieve single-frequency vortex laser output. Patent CN113872031A discloses a single-frequency vortex light laser, which achieves single-frequency vortex laser output by inserting a point defect mirror and an etalon into the resonant cavity. However, in some specific occasions, it is necessary to obtain single-frequency vortex light of a specific chirality, which further increases the technical difficulty.

[0004] Therefore, how to directly obtain chirality-adjustable single-frequency vortex light through a laser is an urgent problem to be solved by technicians in this field. Summary of the invention

[0005] In order to solve the problem in the prior art that it is difficult to generate a chiral controllable single-frequency vortex beam, the present invention provides an off-axis pumped chiral controllable single-frequency vortex laser output device, which can output a single-frequency, narrow-linewidth, low-noise vortex laser by introducing a position offset and an angle offset of the pump light relative to the optical axis through a moving lens.

[0006] An off-axis pumped chiral controllable single-frequency vortex laser output device comprises a pump laser 1, a pump coupling lens 2, a displacement module 3, a single non-planar annular cavity 4, a magnet 5, and a temperature control module 6;

[0007] The pump laser 1 is used to generate pump light; the pump coupling lens 2 is placed on the displacement module 3 and is used to focus the pump light into the single non-planar ring cavity 4; the displacement module 3 is used to move the pump coupling lens 2 upward or downward, and the moving direction is perpendicular to the plane formed by the pump light incident direction and the laser emission direction of the single non-planar ring cavity 4;

[0008] Two magnets 5 are respectively placed in front of and behind the pump light incident surface of the single non-planar ring cavity 4, so that the magnetic field direction at the single non-planar ring cavity 4 is perpendicular to the pump light incident surface;

[0009] The temperature control module 6 is used to maintain the temperature of the single non-planar annular cavity 4 so that the temperature variation does not exceed ±1°C.

[0010] Furthermore, when the displacement module 3 moves the pump coupling lens 2 upward or downward, the calculation method of the displacement M of the pump light relative to the optical axis of the single non-planar annular cavity 4 is:

[0011]

[0012] Wherein, dx is the displacement of the pump coupling lens 2, F is the focal length of the pump coupling lens 2, L is the distance between the pump coupling lens 2 and the single non-planar annular cavity 4, represents the incident point distance offset caused by the displacement dx of the pump coupling lens 2 in the monolithic non-planar annular cavity 4, It represents the angle deviation of the incident point caused by the displacement dx of the pump coupling lens 2 in the monolithic non-planar annular cavity 4.

[0013] Furthermore, the method for obtaining the single-frequency chiral tunable vortex light is as follows:

[0014] Adjust the positions of the pump laser 1 and the pump coupling lens 2 until the pump light passing through the pump coupling lens 2 coincides with the intracavity optical axis of the single non-planar ring cavity 4, so that the laser mode output by the single non-planar ring cavity 4 is a Gaussian mode;

[0015] The pump coupling lens 2 is moved upward or downward by the displacement module 3, so that the pump light is offset from the intracavity optical axis of the single non-planar annular cavity 4, and the pump light is offset relative to the incident angle when it coincides with the intracavity optical axis of the single non-planar annular cavity 4, thereby exciting the output of a single chiral vortex light.

[0016] Furthermore, the single non-planar annular cavity 4 is an Er:YAG crystal, and a dielectric film is coated on the incident surface of the Er:YAG crystal to enhance the transmittance of pump light with a wavelength of 1532nm and to output the s-polarization state portion of the oscillating single-frequency vortex laser with a wavelength of 1645nm.

[0017] Further, the displacement module 3 can move the pump coupling lens 2 upward or downward by 0.4 mm, wherein when the pump coupling lens 2 is moved upward, the angle of the pump light incident on the single non-planar annular cavity 4 is shifted upward, and when the pump coupling lens 2 is moved downward, the angle of the pump light incident on the single non-planar annular cavity 4 is shifted downward, wherein the shift angle is not greater than 5 mrad, and the pump coupling lens 2 makes the spot waist radius of the pump light after focusing less than 0.15 mm.

[0018] Furthermore, the displacement module 3 is an electric lifting platform, a piezoelectric motor or a manual lifting platform.

[0019] Furthermore, the pump laser 1 is a fiber laser or a semiconductor laser, the generated pump light is a Gaussian beam, and the output spectrum matches the absorption peak of Er:YAG.

[0020] Furthermore, when the pump light rotates clockwise in the single non-planar annular cavity 4, the direction of the magnetic field is directed from the pump light incident surface to the outside of the single non-planar annular cavity 4; when the pump light rotates counterclockwise in the single non-planar annular cavity 4, the direction of the magnetic field is directed from the pump light incident surface to the inside of the single non-planar annular cavity 4.

[0021] Beneficial effects:

[0022] 1. The present invention provides an off-axis pumped chirality controllable single-frequency vortex laser output device, which causes the pump coupling lens to deviate from the optical axis through a displacement module, so that the pump light deviates from the optical axis and produces a small angle offset, and utilizes the characteristic that the chirality of the vortex light is sensitive to the incident angle of the pump laser to achieve chirality controllable single-frequency vortex laser output, which can meet the needs of some specific scenarios, such as composite coherent detection, laser communication and other fields; the method for realizing chirality controllable single-frequency vortex laser proposed in the present invention is simple, compact in structure, and highly integrated, and the output laser has the advantages of low noise, narrow line width, good stability, etc.

[0023] 2. The present invention provides an off-axis pumped chirality controllable single-frequency vortex laser output device. The laser resonant cavity used is a single-piece non-planar annular cavity. The resonant cavity and the gain medium are an integral whole. Although the vortex light output cannot be achieved by changing the laser resonant cavity, the present invention innovatively introduces the position offset and angle offset of the pump light by moving the lens only once to achieve vortex light output. The method is simple and effective, and the realized single-frequency vortex laser has the advantages of narrow line width, low noise, high power, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A schematic diagram of an off-axis pumped chirality controllable single-frequency vortex laser output device provided by the present invention;

[0025] 1- pump laser; 2- pump coupling lens; 3- displacement module; 4- single non-planar ring cavity; 5- magnet; 6- temperature control module. DETAILED DESCRIPTION

[0026] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application.

[0027] A vortex beam is a beam that carries orbital angular momentum. It has a spiral phase wavefront and a phase singularity at the center of the beam, forming a donut-shaped hollow ring distribution in the light intensity distribution. As a typical vortex beam, the Laguerre-Gaussian beam can be described as

[0028]

[0029] In the above formula is its spiral phase, and the orbital angular momentum it carries is l is the orbital angular momentum topological charge.

[0030] The chirality of vortex light refers to the positive or negative topological charge of the vortex light. Positive chirality and negative chirality correspond to different wavefront phase rotation modes during vortex light transmission, and also mark the different directions of the Poynting vector, indicating different spiral propagation directions of vortex light energy transmission.

[0031] like Figure 1 As shown, the present invention provides an off-axis pumped chiral controllable single-frequency vortex laser output device, comprising a pump laser 1, a pump coupling lens 2, a displacement module 3, a single non-planar annular cavity 4 made of Er:YAG, two magnets 5, and a temperature control module 6;

[0032] The pump laser 1 is used to generate pump light, and is one of a fiber laser and a semiconductor laser. The generated pump light is a Gaussian beam, and the output spectrum matches the absorption peak of Er:YAG; the pump coupling lens 2 is placed on the displacement module 3, and is used to focus the pump light into the single non-planar ring cavity 4; the displacement module 3 is used to move the pump coupling lens 2 upward or downward, and the moving direction is perpendicular to the pump light incident surface of the single non-planar ring cavity 4; wherein the displacement module is one of an electric lifting platform, a piezoelectric motor, and a manual lifting platform.

[0033] Two magnets 5 are respectively placed in front of and behind the pump light incident surface of the single non-planar annular cavity 4, so that the direction of the magnetic field at the single non-planar annular cavity 4 is perpendicular to the pump light incident surface; specifically, the two magnets 5 make the magnetic field intensity at the single non-planar annular cavity not less than 0.2T, and the magnetic field direction at the single non-planar annular cavity is perpendicular to the incident plane of the single non-planar annular cavity, and when the pump light rotates clockwise in the single non-planar annular cavity, the magnetic field direction points from the incident plane to the outside of the single non-planar annular cavity; when the pump light rotates counterclockwise in the single non-planar annular cavity, the magnetic field direction points from the incident plane to the inside of the single non-planar annular cavity.

[0034] The temperature control module 6 is used to maintain the temperature of the single non-planar annular cavity 4 so that the temperature variation does not exceed ±1°C.

[0035] Furthermore, the pump laser is a continuous fiber laser with an output wavelength of 1532.3nm, the wavelength is locked on the absorption peak of the Er:YAG crystal, and can output a pump light with a power of 40W. The pump coupling lens 2 is a plano-convex lens with a focal length of 150mm, and the surface is coated with a 1400-1700nm anti-reflection film. The displacement module is an electric lifting platform with a maximum stroke of 10mm and an accuracy of <10nm. The single non-planar annular cavity is an Er:YAG crystal with a size of 14mm×12mm×4mm and a doping concentration of 0.5at.%, wherein a dielectric film is coated on the incident surface to increase the transmittance of the pump light with a wavelength of 1532nm and to output the s-polarization state portion of the oscillating single-frequency vortex laser with a wavelength of 1645nm. The single non-planar annular cavity is installed in a heat sink fixture. The magnet 5 is placed before and after the incident surface of the single non-planar annular cavity, so that the magnetic field direction at the single non-planar annular cavity points from the incident surface outside the single non-planar annular cavity to the outside of the single non-planar annular cavity, and the magnetic field strength is 0.5T.

[0036] First, the pump laser 1 and the pump coupling lens 2 are adjusted so that the pump light passing through the pump coupling lens 2 coincides with the intracavity optical axis of the single non-planar ring cavity, so that the laser mode output by the single non-planar ring cavity is a Gaussian mode. At this time, the pump coupling lens 2 is displaced by the displacement module so that the pump light is offset from the optical axis and the pump light has a certain incident angle. Since the pump light deviates from the optical axis, the gain of the fundamental mode Gaussian beam in the resonant cavity is reduced, and the gain of the vortex beam is increased, so that vortex light is generated. Since the pump light has an inclined angle, the output vortex light has only a single chirality. Due to the Faraday rotation effect, the single non-planar ring cavity realizes the unidirectional operation of the non-planar ring cavity, so that the output laser is a narrow linewidth single-frequency laser. Furthermore, when the pump coupling lens 2 is displaced in another direction by the displacement module, the output vortex light can have another chirality.

[0037] The mechanism of the present invention to achieve vortex light output through displacement lens is described as follows:

[0038] When the lens is shifted, the pump light is offset from the optical axis of the single non-planar ring cavity. The offset M can be described as

[0039]

[0040] Wherein, dx is the displacement of the pump coupling lens 2, F is the focal length of the pump coupling lens 2, L is the distance between the pump coupling lens 2 and the single non-planar annular cavity 4, represents the incident point distance offset caused by the displacement dx of the pump coupling lens 2 in the monolithic non-planar annular cavity 4, It represents the angle offset of the incident point caused by the displacement dx of the pump coupling lens 2 in the monolithic non-planar annular cavity 4. Therefore, the displacement dx of the pump coupling lens 2 simultaneously changes two variables of the incident light, namely, the position of the incident point and the angle offset of the incident point.

[0041] It should be noted that the displacement module can displace the pump coupling lens upward or downward by 0.4 mm. Displacing the pump coupling lens upward causes the pump light to shift upward at a small angle, and displacing the pump coupling lens downward causes the pump light to shift downward at a small angle, and the inclination angle is not greater than 5 mrad; and the pump coupling lens causes the waist radius of the spot after focusing the pump light to be less than 0.15 mm.

[0042] Because the position of the incident point of the pump light is offset, the pump light undergoes image rotation along the optical axis of the single non-planar ring cavity, stimulating vortex light output. When the pump light is incident, the pump light is a Gaussian beam, which has a higher degree of overlap with the Gaussian mode of the laser resonant cavity, and the threshold of the Gaussian beam is lower. Therefore, the laser excited is a Gaussian beam, which is also a traditional single non-planar ring cavity laser. When the incident point of the pump light is offset, the gain of the optical axis area is reduced, and the threshold of the Gaussian beam is significantly increased. At the same time, due to the increased overlap between the offset pump light and the vortex beam, the threshold of the vortex light is reduced, thus stimulating the generation of vortex light beam output.

[0043] Because the incident angle of the pump light is offset, different incident angles will superimpose the rotation angle of the offset optical axis of the single non-planar ring cavity, breaking the symmetry of the single non-planar ring cavity and stimulating the output of a single chiral vortex light. Positive chirality and negative chirality correspond to different spiral propagation directions of vortex light energy transmission. Therefore, the pump light rotating along the optical axis can reduce the oscillation threshold of the chiral vortex light with a high degree of overlap, thereby stimulating this single chiral vortex light.

[0044] The present invention adopts Er:YAG as the gain medium of the single-frequency vortex light laser. Er:YAG is a quasi-three-level structure with a significant reabsorption effect. In the process of exciting vortex light, there is a significant mode loss in the non-overlapping area with the pump light, so it is more conducive to exciting and generating vortex light with adjustable chirality.

[0045] It should be noted that the prior art realizes chiral vortex light output by changing the components of the laser resonant cavity and breaking the symmetry of the laser resonant cavity; the laser resonant cavity used in the present invention is a single-piece non-planar ring cavity, and the resonant cavity and the gain medium are an integral whole. Obviously, it is impossible to realize vortex light output by changing the components of the laser resonant cavity. The present invention innovatively introduces the position offset and angle offset of the pump light by moving the lens at the same time to realize vortex light output. In other words, the present invention only needs to move the lens once to realize the conversion of the laser from a single-frequency Gaussian beam to a single-frequency chiral controllable vortex beam. The present invention has the advantages of simple and effective method, and the realized single-frequency vortex laser has the advantages of narrow line width, low noise, and high power.

[0046] In summary, the present invention discloses an off-axis pumped chirality controllable single-frequency vortex laser output device, including: a pump laser, a pump coupling lens, a displacement module, a single non-planar annular cavity, a magnet, and a temperature control module; the pump laser is used to provide pump laser; the pump coupling lens is used to focus the pump laser into the single non-planar annular cavity; the displacement module is used to move the pump coupling lens; the single non-planar annular cavity is a laser gain medium and a resonant cavity; the magnet is used to generate a magnetic field to achieve unidirectional operation of the single non-planar annular cavity; the temperature control module is used to control the temperature of the single non-planar annular cavity. The present invention moves the pump coupling lens through the displacement module, so that the pump light has an off-axis pumped single non-planar annular cavity with an inclined angle, and generates a single-frequency vortex laser with adjustable chirality. This method generates a single-frequency vortex light with adjustable chirality, which has high integration, compact structure, and simplicity.

[0047] Of course, the present invention may have many other embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art may certainly make various corresponding changes and modifications based on the present invention, but these corresponding changes and modifications should all fall within the scope of protection of the claims attached to the present invention.

Claims

1. An off-axis pumped chiral controllable single-frequency vortex laser output device, characterized in that: It comprises a pump laser (1), a pump coupling lens (2), a displacement module (3), a single non-planar ring cavity (4), a magnet (5), and a temperature control module (6); The pump laser (1) is used to generate pump light; the pump coupling lens (2) is placed on a displacement module (3) and is used to focus the pump light into a single non-planar annular cavity (4); the displacement module (3) is used to move the pump coupling lens (2) upward or downward, and the moving direction is perpendicular to a plane formed by a pump light incident direction and a laser emission direction of the single non-planar annular cavity (4); Two magnets (5) are respectively placed in front of and behind the pump light incident surface of the single non-planar annular cavity (4), so that the magnetic field direction at the single non-planar annular cavity (4) is perpendicular to the pump light incident surface; The temperature control module (6) is used to maintain the temperature of the single non-planar annular cavity (4) so ​​that the temperature variation does not exceed ±1°C.

2. An off-axis pumped chiral controllable single-frequency vortex laser output device as claimed in claim 1, characterized in that: When the displacement module (3) moves the pump coupling lens (2) upward or downward, the calculation method of the displacement M of the pump light relative to the optical axis of the single non-planar annular cavity (4) is as follows: Wherein, dx is the displacement of the pump coupling lens (2), F is the focal length of the pump coupling lens (2), L is the distance between the pump coupling lens (2) and the single-piece non-planar annular cavity (4), represents the incident point distance offset caused by the displacement dx of the pump coupling lens (2) in the monolithic non-planar annular cavity (4), The displacement dx of the pump coupling lens (2) represents the angle deviation of the incident point in the monolithic non-planar annular cavity (4).

3. The off-axis pumped chiral controllable single-frequency vortex laser output device according to claim 1, characterized in that: The method for obtaining single-frequency chiral tunable vortex light is as follows: The positions of the pump laser (1) and the pump coupling lens (2) are adjusted until the pump light passing through the pump coupling lens (2) coincides with the intracavity optical axis of the single non-planar ring cavity (4), so that the laser mode output by the single non-planar ring cavity (4) is a Gaussian mode; The pump coupling lens (2) is moved upward or downward by a displacement module (3), so that the pump light is offset from the intracavity optical axis of the single non-planar annular cavity (4), and the pump light is offset relative to the incident angle when it coincides with the intracavity optical axis of the single non-planar annular cavity (4), thereby exciting the output of a single chiral vortex light.

4. The off-axis pumped chiral controllable single-frequency vortex laser output device according to claim 1, characterized in that: The single non-planar annular cavity (4) is an Er:YAG crystal, and a dielectric film is plated on the incident surface of the Er:YAG crystal to enhance the transmittance of pump light with a wavelength of 1532nm and to output the s-polarization state part of the oscillating single-frequency vortex laser with a wavelength of 1645nm.

5. The off-axis pumped chiral controllable single-frequency vortex laser output device according to claim 1, characterized in that: The displacement module (3) is capable of moving the pump coupling lens (2) upward or downward by 0.4 mm, wherein when the pump coupling lens (2) is moved upward, the angle at which the pump light is incident on the single non-planar annular cavity (4) is shifted upward, and when the pump coupling lens (2) is moved downward, the angle at which the pump light is incident on the single non-planar annular cavity (4) is shifted downward, wherein the shift angle is not greater than 5 mrad, and the pump coupling lens (2) enables the beam waist radius of the pump light after focusing to be less than 0.15 mm.

6. The off-axis pumped chiral controllable single-frequency vortex laser output device according to claim 1, characterized in that: The displacement module (3) is an electric lifting platform, a piezoelectric motor or a manual lifting platform.

7. The off-axis pumped chiral controllable single-frequency vortex laser output device according to claim 1, characterized in that: The pump laser (1) is a fiber laser or a semiconductor laser, the pump light generated is a Gaussian beam, and the output spectrum matches the absorption peak of Er:YAG.

8. The off-axis pumped chiral controllable single-frequency vortex laser output device according to claim 1, characterized in that: When the pump light rotates clockwise in the single non-planar annular cavity (4), the direction of the magnetic field is directed from the pump light incident surface to the outside of the single non-planar annular cavity (4); when the pump light rotates counterclockwise in the single non-planar annular cavity (4), the direction of the magnetic field is directed from the pump light incident surface to the inside of the single non-planar annular cavity (4).

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