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

Abstract

The application provides an off-axis pump chiral controllable single-frequency vortex laser output device, a pump coupling lens is caused to deviate from an optical axis through a displacement module, pump light deviates from the optical axis and produces a small-angle deviation, a chiral controllable single-frequency vortex laser output is realized by using the characteristic that vortex light chirality is sensitive to an incident angle of a pump laser, and the requirement of some specific scenes, such as 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 application 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] This invention belongs to the field of laser technology, and particularly relates to a single-frequency chiral controllable vortex laser. Background Technology

[0002] A vortex beam is a type of optical field with a helical phase and a ring-shaped intensity distribution. It has a phase singularity at its center, and all photons within the beam carry orbital angular momentum. This type of beam is widely used in many fields, including optical communication, quantum information, biological microscopy, and rotating Doppler detection.

[0003] The most common output mode of lasers that directly generate vortex beams is multi-longitudinal mode, while reports on single-frequency vortex lasers are relatively few. Patent CN115579719A discloses a single-frequency vortex laser that uses an axonoconical mirror to convert a Gaussian beam into a ring beam, and then uses this ring beam to pump a single non-planar ring cavity, achieving single-frequency vortex laser output. Patent CN113872031A discloses a single-frequency vortex laser that achieves single-frequency vortex laser output through a point-defect mirror and the insertion of an etalon within the resonant cavity. However, in certain specific applications, it is necessary to obtain single-frequency vortex light with specific chirality, which further increases the technical difficulty.

[0004] Therefore, how to directly obtain chiral tunable single-frequency vortex light through a laser is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] To address the problem of generating chiral controllable single-frequency vortex beams in existing technologies, this invention provides an off-axis pumped chiral controllable single-frequency vortex laser output device. By introducing position and angle offsets of the pump light relative to the optical axis through a moving lens, it can output a single-frequency, narrow-linewidth, and low-noise vortex laser.

[0006] An off-axis pumped chiral controllable single-frequency vortex laser output device includes 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 monolithic 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 the plane formed by the pump light incident direction and the laser emission direction of the monolithic non-planar annular cavity 4.

[0008] Two magnets 5 are placed in front of and behind the pump light incident surface of the single non-planar annular cavity 4, respectively, so that the magnetic field direction at the single non-planar annular 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 its temperature change does not exceed ±1℃.

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

[0011]

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

[0013] Furthermore, the method for obtaining 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 through the pump coupling lens 2 coincides with the optical axis inside the single non-planar ring cavity 4, so that the laser mode output by the single non-planar ring cavity 4 is Gaussian mode.

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

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

[0017] Furthermore, the displacement module 3 can move the pump coupling lens 2 upward or downward by 0.4 mm. 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. 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. The shift angle is not greater than 5 mrad, and the pump coupling lens makes the beam waist radius of the focused pump light 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, and the pump light it generates is a Gaussian beam, and the output spectrum matches the absorption peak of Er:YAG.

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

[0021] Beneficial effects:

[0022] 1. This invention provides an off-axis pumped chiral controllable single-frequency vortex laser output device. A displacement module causes the pump coupling lens to deviate from the optical axis, resulting in a small-angle offset of the pump light. Utilizing the sensitivity of vortex light chirality to the incident angle of the pump laser, chiral controllable single-frequency vortex laser output is achieved, meeting the needs of certain specific scenarios, such as composite coherent detection and laser communication. The method for achieving chiral controllable single-frequency vortex laser proposed in this invention is simple, compact, and highly integrated, and the output laser has advantages such as low noise, narrow linewidth, and good stability.

[0023] 2. This invention provides an off-axis pumped chiral controllable single-frequency vortex laser output device. The laser resonator used is a single non-planar ring cavity, and the resonator and the gain medium are an integral unit. Although it is impossible to achieve vortex light output by changing the laser resonator, this invention innovatively achieves vortex light output by only moving the lens once to introduce position and angle offset of the pump light. The method is simple and effective, and the achieved single-frequency vortex laser has advantages such as narrow linewidth, low noise, and high power. Attached Figure Description

[0024] Figure 1 A schematic diagram of an off-axis pumped chiral 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 annular cavity; 5-Magnet; 6-Temperature control module. Detailed Implementation

[0026] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings.

[0027] A vortex beam is a type of beam carrying orbital angular momentum. It possesses a helical phase wavefront and a phase singularity at its center, resulting in a hollow, ring-shaped intensity distribution resembling a donut. The Laguerre-Gaussian beam, as a typical example of a vortex beam, can be described as...

[0028]

[0029] In the above formula Given its helical phase, the magnitude of its orbital angular momentum is... l is the orbital angular momentum topological charge.

[0030] The chirality of vortex light refers to the sign of its topological charge. Positive and negative chirality correspond to different wavefront phase rotation patterns during vortex light propagation, and also indicate different directions of the Poynting vector, indicating different helical 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, including a pump laser 1, a pump coupling lens 2, a displacement module 3, a single non-planar annular cavity 4 made of Er:YAG material, 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 or a semiconductor laser. The generated pump light is a Gaussian beam, and its 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 monolithic non-planar annular cavity 4. The displacement module 3 is used to move the pump coupling lens 2 up or down, and the direction of movement is perpendicular to the incident surface of the pump light of the monolithic non-planar annular cavity 4. The displacement module is one of an electric lifting platform, a piezoelectric motor, or a manual lifting platform.

[0033] Two magnets 5 are placed in front of and behind the pump light incident surface of the single non-planar annular cavity 4, respectively, so that the magnetic field direction at the single non-planar annular cavity 4 is perpendicular to the pump light incident surface. Specifically, the two magnets 5 ensure that the magnetic field strength at the single non-planar annular cavity is 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. When the pump light rotates clockwise inside 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 inside 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 its temperature change does not exceed ±1℃.

[0035] Furthermore, the pump laser is a continuous fiber laser with an output wavelength of 1532.3 nm, the wavelength of which is locked to the absorption peak of the Er:YAG crystal, and it can output pump light with a power of 40W. The pump coupling lens 2 is a plano-convex lens with a focal length of 150 mm and an anti-reflection coating of 1400-1700 nm on its surface. The displacement module is an electric lifting platform with a maximum stroke of 10 mm and an accuracy of <10 nm. The single non-planar ring cavity is an Er:YAG crystal with dimensions of 14 mm × 12 mm × 4 mm and a doping concentration of 0.5 at.%. The incident surface is coated with a dielectric film that enhances the anti-reflection effect on pump light with a wavelength of 1532 nm and protects the s-polarization portion of the oscillating single-frequency vortex laser with a wavelength of 1645 nm. The single non-planar ring cavity is mounted in a heat sink fixture. The magnet 5 is placed in front of and behind the incident surface of the single non-planar annular cavity, so that the direction of the magnetic field at the single non-planar annular cavity is 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 pump coupling lens 2 are adjusted so that the pump light passing through the pump coupling lens 2 coincides with the optical axis of the monolithic non-planar ring cavity, making the output laser mode of the monolithic non-planar ring cavity Gaussian. Then, the pump coupling lens 2 is displaced via a displacement module, causing the pump light to deviate from the optical axis and simultaneously giving it a certain incident angle. Because the pump light deviates from the optical axis, the gain of the fundamental mode Gaussian beam in the resonant cavity decreases, while the gain of the vortex beam increases, generating vortex light. Due to the tilt angle of the pump light, the output vortex light has only a single chirality. Due to the Faraday rotation effect, the monolithic non-planar ring cavity achieves unidirectional operation, resulting in a narrow-linewidth, single-frequency laser output. Furthermore, when the pump coupling lens 2 is displaced in another direction via the displacement module, the output vortex light can acquire another chirality.

[0037] The mechanism by which this invention achieves vortex light output through a displacement lens is described as follows:

[0038] When using a displacement lens, the pump light is deflected from the optical axis of the monolithic non-planar annular cavity. The deflection amount M can be described as...

[0039]

[0040] Where dx is the displacement of the pump coupling lens 2, F is the focal length of the pump coupling lens 2, and L is the distance between the pump coupling lens 2 and the single non-planar annular cavity 4. The displacement dx of the pump coupling lens 2 causes the incident point distance shift in the monolithic non-planar annular cavity 4. This represents the angular shift of the incident point caused by the displacement dx of the pump-coupled lens 2 within the monolithic non-planar annular cavity 4. Therefore, the displacement dx of the pump-coupled lens 2 simultaneously alters two variables of the incident light: the position of the incident point and the angular shift of the incident point.

[0041] It should be noted that the displacement module can move the pump coupling lens upward or downward by 0.4 mm. Moving the pump coupling lens upward causes the pump light to shift upward at a small angle, and moving the pump coupling lens downward causes the pump light to shift downward at a small angle, with the tilt angle not exceeding 5 mrad. Furthermore, the pump coupling lens ensures that the beam waist radius of the focused pump light is less than 0.15 mm.

[0042] Because the incident point of the pump light is shifted, the pump light rotates along the optical axis of the monolithic non-planar ring cavity, exciting vortex light output. When the pump light is normally incident, it is a Gaussian beam with a higher degree of overlap with the Gaussian mode of the laser resonator. The Gaussian beam exhibits a lower threshold, thus generating a Gaussian beam, which is typical of traditional monolithic non-planar ring cavity lasers. When the incident point of the pump light shifts, the gain in the optical axis region decreases, and the threshold of the Gaussian beam increases significantly. Simultaneously, due to the increased overlap between the shifted pump light and the vortex beam, the threshold of the vortex beam is lowered, thus exciting a vortex light beam output.

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

[0044] This invention uses Er:YAG as the gain medium for a single-frequency vortex laser. Er:YAG is a quasi-three-level structure with a significant reabsorption effect. During the excitation of vortex light, there is significant mode loss in the non-overlapping region with the pump light, which is more conducive to the excitation of chiral tunable vortex light.

[0045] It should be noted that existing technologies achieve chiral vortex beam output by altering the components of the laser resonator to break its symmetry. The laser resonator used in this invention is a single, non-planar ring cavity, with the resonator and gain medium forming a single unit. Clearly, it is impossible to achieve vortex beam output by changing the components of the laser resonator. This invention innovatively achieves vortex beam output by simultaneously introducing position and angle shifts in the pump light through lens movement. In other words, this invention only requires moving the lens once to convert the laser beam from a single-frequency Gaussian beam to a single-frequency chiral controllable vortex beam. This invention is simple and effective, and the resulting single-frequency vortex laser has advantages such as narrow linewidth, low noise, and high power.

[0046] In summary, this invention discloses an off-axis pumped chiral controllable single-frequency vortex laser output device, comprising: 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 provides the pump laser; the pump coupling lens focuses the pump laser into the single non-planar annular cavity; the displacement module moves the pump coupling lens; the single non-planar annular cavity serves as both the laser gain medium and the resonant cavity; the magnet generates a magnetic field to enable unidirectional operation of the single non-planar annular cavity; and the temperature control module controls the temperature of the single non-planar annular cavity. This invention, by moving the pump coupling lens through the displacement module, allows the pump light to pump the single non-planar annular cavity off-axis at an angle, generating a chiral tunable single-frequency vortex laser. This method of generating chiral tunable single-frequency vortex light is highly integrated, compact, and simple.

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

Claims

1. A device for off-axis pump chiral controllable single-frequency vortex laser output, characterized in that, The application relates to a single-frequency chiral adjustable vortex light acquisition device and a method thereof. The pump laser (1) is used for generating pump light; the pump coupling lens (2) is placed on the displacement module (3) and is used for focusing the pump light into the single-piece non-planar ring cavity (4); the displacement module (3) is used for moving the pump coupling lens (2) upward or downward, and the moving direction is perpendicular to a plane formed by the pump light incidence direction and the laser emission direction of the single-piece non-planar ring cavity (4); Two magnets (5) are placed in front of and behind the pump light incidence surface of the single-piece non-planar ring cavity (4), and the two magnets (5) are located outside the single-piece non-planar ring cavity (4), so that the magnetic field direction of the single-piece non-planar ring cavity (4) is perpendicular to the pump light incidence surface. The temperature control module (6) is used for maintaining the temperature of the single-piece non-planar ring cavity (4) so that the temperature change is not more than + / -1 DEG C. The single-frequency chiral adjustable vortex light acquisition method 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) is coincident with the cavity optical axis of the single-piece non-planar ring cavity (4), so that the laser mode output by the single-piece non-planar ring cavity (4) is a Gaussian mode; The pump coupling lens (2) is moved upward or downward by the displacement module (3), so that the pump light is offset from the cavity optical axis of the single-piece non-planar ring cavity (4), and the incidence angle of the pump light is offset relative to the incidence angle when the pump light is coincident with the cavity optical axis of the single-piece non-planar ring cavity (4), thereby exciting single-chiral vortex light output.

2. A device for off-axis pump-induced chirp-controlled single-frequency vortex laser output as claimed in claim 1, wherein, The displacement module (3) moves the pumping coupling lens (2) up or down, and the offset of the pumping light relative to the optical axis of the monolithic non-planar ring cavity (4) occurs The calculation method is as follows: wherein is a displacement amount of the pump coupling lens (2), is a focal length of the pump coupling lens (2), is a distance between the pump coupling lens (2) and the single-block non-planar ring cavity (4), denotes a displacement amount of the pump coupling lens (2) is a distance of the incident point from the center of the single-block non-planar ring cavity (4), denotes a displacement amount of the pump coupling lens (2) is an angle of the incident point from the center of the single-block non-planar ring cavity (4).

3. A device for off-axis pump-induced chirp-managed single-frequency vortex laser output as claimed in claim 1, wherein, The single-piece non-planar ring cavity (4) is an Er:YAG crystal, and an antireflection film is coated on the incidence surface of the Er:YAG crystal, the antireflection film being used for transmitting pump light with a wavelength of 1532 nm and transmitting s-polarization state part of oscillation single-frequency vortex laser with a wavelength of 1645 nm.

4. A device for off-axis pump-induced chirp-managed single-frequency vortex laser output as claimed in claim 1, wherein, 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 to the single-piece non-planar ring cavity (4) is upwardly offset, and when the pump coupling lens (2) is moved downward, the angle of the pump light incident to the single-piece non-planar ring cavity (4) is downwardly offset, wherein the offset angle is not more than 5 mrad, and the waist radius of the light spot of the pump light focused by the pump coupling lens (2) is less than 0.15 mm.

5. A device for off-axis pump-induced chirp-managed single-frequency vortex laser output as claimed in claim 1, wherein, The displacement module (3) is an electric lifting platform, a piezoelectric motor or a manual lifting platform.

6. A device for off-axis pump- ing of chiral controllable single-frequency vortex laser output as claimed in claim 1, wherein, 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 the Er:YAG.

7. A device for off-axis pump- ing of chiral controllable single-frequency vortex laser output as claimed in claim 1, wherein, When the pump light rotates clockwise in the single-piece non-planar ring cavity (4), the magnetic field direction points from the pump light incidence surface to the outside of the single-piece non-planar ring cavity (4); when the pump light rotates counterclockwise in the single-piece non-planar ring cavity (4), the magnetic field direction points from the pump light incidence surface to the inside of the single-piece non-planar ring cavity (4).

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