A multi-mode vortex laser with adjustable order

Abstract

The application discloses a multi-mode vortex laser with adjustable order, comprising: a cavity lens coated with a laser wavelength anti-reflection film system, a first laser output mirror and a second laser output mirror, both of which are plane mirrors, and both of which are coated with a film system partially transmitting laser wavelength on one side and an anti-reflection film system for laser wavelength on the other side; a high-order Laguerre-Gaussian beam is focused by the cavity lens, and the focused beam waist positions of each-order Laguerre-Gaussian mode vortex light are separated under the action of spherical aberration of the cavity lens, and the higher the mode order and the larger the spot size, the closer the focused beam waist of the mode to the cavity lens; the positions of the first laser output mirror and the second laser output mirror are adjusted so as to be located at the waist positions of a certain mode, and the first laser output mirror and the second laser output mirror located at different positions provide feedback for two different-order Laguerre-Gaussian mode vortex lights, so that multi-mode vortex laser oscillation and output are formed.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of lasers, in particular to a multi-mode vortex laser with adjustable mode order. BACKGROUND

[0002] Vortex beams have a helical wavefront, around the center, its wavefront phase changes by an integer l times of 2π, each photon in the beam carries orbital angular momentum. For the most typical Laguerre-Gaussian beam, l is its angular index; due to the phase singularity in the center of the vortex beam, its light intensity is distributed in a hollow ring, and the related characteristics make the vortex beam have important applications in optical tweezers, quantum communication, micro-nano manufacturing, etc. The methods of generating vortex beams include passive and active methods. Passive methods modulate and transform the existing Gaussian beams or Hermite Gaussian beams outside the cavity to obtain vortex light. Active methods control the gain and loss of laser modes in the resonant cavity by shaping the pump light and adjusting the size and pattern of the defect point, so as to realize mode selection and generate vortex light oscillation output [1] .

[0003] In quantum entanglement, spatial optical communication and other applications, vortex light sources containing multiple modes are often used for multiplexing to improve system performance. However, the mode purity and power ratio of multi-mode beams are often difficult to control, and mode competition will also cause fluctuations in light intensity, so a controllable multi-mode vortex beam generation method is very important. Among the currently reported methods of generating multi-mode vortex beams, only the literature [2] proposes to etch multiple concentric circles of different sizes on the laser resonant cavity mirror to control the loss of each mode with different sizes, thereby realizing multi-mode vortex light output. However, etching a complex pattern on the cavity mirror requires very high processing technology and is difficult to prepare; on the other hand, after the device is prepared, the corresponding mode order is also determined, and it is difficult to independently adjust the mode order flexibly; moreover, the defect point is easily further damaged by the high-intensity laser in the cavity, causing the laser mode to change, and even unable to continue to work. Therefore, it is difficult for the prior art to realize multi-mode vortex light output with adjustable mode order.

[0004] REFERENCES

[0005] [1] A. Forbes, “Structured light from lasers,” Laser Photonics Rev. 13(11), 1900140 (2019).

[0006] [2] Method for directly generating multi-vortex beams in a cavity, Chinese invention patent, authorization number CN 109031674 B Summary of the Invention

[0007] This invention provides a multi-mode vortex laser with adjustable order. It utilizes multiple laser output mirrors located at different positions to provide feedback to Laguerre-Gaussian vortex lasers of different orders, thereby achieving oscillating output of the multi-mode vortex laser with adjustable order. See the description below for details:

[0008] A multimode vortex laser with tunable order, the laser comprising:

[0009] The laser total reflection mirror is coated with a pump light wavelength antireflection and laser wavelength high reflectivity film system; the laser gain medium is coated with a pump light and laser wavelength antireflection film system; the cavity lens is coated with a laser wavelength antireflection film system; the first laser output mirror and the second laser output mirror are both plane mirrors, both of which are coated with a film system that allows partial transmission of laser wavelength on one side and a film system that increases laser wavelength on the other side.

[0010] A higher-order Laguerre-Gaussian beam is focused by the cavity lens. Under the spherical aberration of the cavity lens, the beam waist of the focused beam will be separated. The higher the order of the mode and the larger the spot size, the closer the beam waist of the focused beam is to the cavity lens.

[0011] Adjust the positions of the first and second laser output mirrors so that they are located at the waist position of a certain mode. The first and second laser output mirrors, located at different positions, provide feedback for two Laguerre-Gaussian vortex lights of different orders, so as to form multi-mode vortex laser oscillation and output.

[0012] The first laser output mirror is arranged such that the side coated with the laser wavelength antireflection film faces into the laser resonant cavity composed of the gain medium and the intracavity lens. The second laser output mirror is arranged such that the side coated with the laser wavelength partial film faces into the laser resonant cavity.

[0013] Preferably, when the generated vortex order is high, the aperture of the laser gain medium and the intracavity lens is larger than the size of the oscillating high-order vortex beam spot. Where w is the fundamental mode spot size determined by the ABCD matrix of the resonant cavity, and p and m are the radial and angular indices of the higher-order vortex light, respectively.

[0014] Preferably, the radius of curvature of the laser total reflection mirror is ≤100mm, or a short focal length lens with a focal length ≤100mm is added nearby.

[0015] The laser gain medium is: Nd:YVO4, Nd:YAG, Ti:Sa, or laser glass or laser ceramics doped with Nd, Yb, or Er.

[0016] The beneficial effects of the technical solution provided by this invention are:

[0017] 1) This invention utilizes two laser output mirrors located at different positions to provide feedback to vortex light of different modes, thereby generating multi-mode vortex laser output with easily adjustable order. No special components are required for fabrication and use. The method is simple, convenient, and cost-effective.

[0018] 2) This invention utilizes a single pump light and laser crystal to generate multi-mode vortex lasers. The structure is simple, and the spot size of the vortex lasers of different modes is different, so the gain regions are different. There is no gain competition, which makes it more stable and has a high utilization rate of pump light. Attached Figure Description

[0019] Figure 1 A schematic diagram of the optical path of a multimode vortex laser with adjustable order provided by the present invention;

[0020] Figure 2 A schematic diagram illustrating the relationship between the beam focal position and spot size under spherical aberration in an embodiment of a multimode vortex laser with adjustable order provided by the present invention.

[0021] Figure 3 This is a schematic diagram illustrating the relationship between the vortex mode order and the position of the laser output mirror in an embodiment of a multimode vortex laser with adjustable order provided by the present invention.

[0022] Appendix Figure 1 The list of components represented by each number is as follows:

[0023] 1: Pump source; 2: Laser total reflection mirror;

[0024] 3: Laser gain medium; 4: Intracavity lens;

[0025] 5: First laser output mirror; 6: Second laser output mirror. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below.

[0027] Example 1

[0028] A multimode vortex laser with tunable order, see [link to documentation]. Figure 1 The laser includes: a pump source 1, a laser total reflection mirror 2, a laser gain medium 3, an intracavity lens 4, a first laser output mirror 5, and a second laser output mirror 6.

[0029] Among them, the laser total reflection mirror 2 is coated with a film system that enhances the transmission of pump light wavelength and provides high reflection of laser wavelength; the laser gain medium 3 is coated with a film system that enhances the transmission of pump light and laser wavelength; the cavity lens 4 is coated with a film system that enhances the transmission of laser wavelength; the first laser output mirror 5 and the second laser output mirror 6 are both coated with a film system that allows partial transmission of laser wavelength on one side and a film system that enhances the transmission of laser wavelength on the other side.

[0030] The laser total reflection mirror 2 and the cavity lens 4 are relatively far apart, so the laser beam transmitted to the cavity lens 4 has a large spot size; the first laser output mirror 5 and the second laser output mirror 6 are both plane mirrors; the cavity lens 4 is an ordinary spherical lens with spherical aberration.

[0031] The beam waist position of the higher-order Laguerre-Gaussian beam after focusing by intracavity lens 4 is given by the following formula:

[0032]

[0033] Where l' is the distance between the focused beam waist and the intracavity lens 4, l is the distance between the focused beam waist and the intracavity lens 4, f is the focal length of the intracavity lens 4, W is the spot size, λ is the laser wavelength, and p and m are the radial and angular indices of the Laguerre-Gaussian beam, respectively.

[0034] Because the Laguerre-Gaussian vortex beams of different orders have different beam sizes, their beam waists will separate due to the spherical aberration of the intracavity lens 4. The higher the order and the larger the spot size of the mode, the closer the beam waist of the focused beam will be to the intracavity lens 4. Considering that the first laser output mirror 5 and the second laser output mirror 6 are both plane mirrors, according to the requirement of self-reproduction of laser resonator modes, only modes whose beam waists are located on the plane mirrors after being focused by the intracavity lens 4 can oscillate within the cavity. Therefore, the first laser output mirror 5 and the second laser output mirror 6, located at different positions, can provide feedback for two Laguerre-Gaussian vortex beams of different orders, enabling them to form multi-mode vortex laser oscillation and output, while other modes suffer greater losses and cannot oscillate. By adjusting the positions of the first laser output mirror 5 and the second laser output mirror 6 so that they are located at the beam waist position of a certain mode, the order of the multi-mode vortex laser can be tuned separately.

[0035] Considering the thickness of the optical lenses, the preferred arrangement of the first laser output mirror 5 is that the side coated with the laser wavelength antireflection film faces into the laser resonant cavity (i.e., towards the gain medium 3 and the cavity lens 4), and the side coated with the laser wavelength partial reflection film faces outward from the laser resonant cavity (i.e., towards the second laser output mirror 6). The preferred arrangement of the second laser output mirror 6 is that the side coated with the laser wavelength partial reflection film faces into the laser resonant cavity (towards the first laser output mirror 5). This allows the spacing between the partial reflection films used to provide feedback for different modes of vortex light to be adjusted within a large dynamic range, thereby controlling the order of multi-mode vortex light without being limited by the thickness of the lenses.

[0036] Preferably, when the generated vortex light order is high, the aperture of the laser gain medium 3 and the intracavity lens 4 should be larger than the size of the oscillating high-order vortex light spot.

[0037] Preferably, the laser total reflection mirror 2 should have a small radius of curvature (or a short focal length lens should be added nearby) to compress the laser beam waist size in the vicinity, so that the intracavity lens 4 has a larger spot size to enhance spherical aberration and achieve better mode selection effect.

[0038] In summary, the embodiments of the present invention provide feedback to Laguerre-Gaussian vortex lasers of different orders by using multiple laser output mirrors located at different positions, thereby achieving multi-mode vortex laser oscillation output with adjustable order and meeting various needs in practical applications.

[0039] Example 2

[0040] This invention provides a multi-mode vortex laser with adjustable order, which includes: a pump source 1, a laser total reflection mirror 2, a laser gain medium 3, an intracavity lens 4, a first laser output mirror 5, and a second laser output mirror 6.

[0041] Pump source 1 is an 808nm semiconductor laser; laser total reflection mirror 2 is a plano-concave mirror with a concave surface curvature radius of 50mm, facing into the cavity, with 808nm pump light antireflection coatings on both sides and a 1064nm laser high reflectivity coating on the concave surface; laser gain medium 3 is an a-cut Nd:YVO4 crystal, 4×4×10mm. 3 The doping concentration is 0.3 at.%, and it is coated with an 808nm pump light and 1064nm laser anti-reflection coating system; the cavity lens 4 is a K9 material spherical biconvex lens with a focal length of 51.8mm, and both are coated with a 1064nm laser anti-reflection coating system; the first laser output mirror 5 and the second laser output mirror 6 are both flat mirrors, and are coated with a 1064nm laser transmittance T=5% and T=10% coating system, respectively.

[0042] The laser total reflection mirror 2 is placed close to the laser gain medium 3; the cavity lens 4 is about 150mm away from the laser gain medium 3; the first laser output mirror 5, with a partially reflective film coated on one side, is about 50mm away from the cavity lens 4, and its position can be finely adjusted; the second laser output mirror 6 is placed close to the first laser output mirror 5, and its position can be finely adjusted.

[0043] In this case, by calculating the spherical aberration of the intracavity lens 4 and according to the above equation (1), the actual focal point position after focusing by the intracavity lens 4 can be obtained, such as... Figure 2 As shown. Based on cavity mode theory, the fundamental mode spot size at lens 4 within the cavity is calculated to be ~800 μm. The order of LG can be determined based on the optical field distribution of the Laguerre-Gaussian vortex light. 0,m The spot size of the vortex light in the mode is used to determine the relationship between the position of the laser output mirror relative to the intracavity lens and the corresponding oscillation mode, based on the spherical aberration of the lens. Figure 3 As shown, by finely adjusting the positions of the first laser output mirror 5 and the second laser output mirror 6, the corresponding multi-mode vortex laser output can be obtained.

[0044] In the above embodiments, the laser gain medium can be laser crystals such as Nd:YVO4, Nd:YAG (neodymium-doped yttrium aluminum garnet), and Ti:Sa (titanium-doped sapphire), or commonly used laser gain media such as laser glass or laser ceramics doped with Nd, Yb (ytterbium), Er (erbium), or other luminescent ions. The corresponding pump source wavelength and coating wavelength can correspond to the absorption peak and emission peak of the laser gain medium. This embodiment of the invention does not limit this.

[0045] In this embodiment of the invention, the focal length of the intracavity lens 4 is not specifically limited. As long as a suitable focal length is selected so that the beam produces obvious spherical aberration after focusing, it is acceptable.

[0046] In summary, the purpose of this invention is to use spherical aberration to spatially separate the optical paths of Laguerre-Gaussian vortex beams of different modes, and to use two laser output mirrors located at different positions to provide feedback for vortex beams of different orders, thereby realizing multi-mode vortex laser oscillation output; by finely adjusting the position of the laser output mirrors, the order of the vortex beam can be conveniently adjusted.

[0047] Unless otherwise specified, the model numbers of the various devices in this embodiment of the invention are not limited, and any device that can perform the above functions is acceptable.

[0048] Those skilled in the art will understand that the accompanying drawings are merely schematic diagrams of a preferred embodiment, and the sequence numbers of the above embodiments of the present invention are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0049] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A multimode vortex laser with adjustable order, characterized in that, The laser utilizes multiple laser output mirrors located at different positions to provide feedback to Laguerre-Gaussian vortex lasers of different orders, thereby achieving oscillating output of multi-mode vortex lasers with adjustable order. The laser includes: The laser total reflection mirror is coated with a pump light wavelength antireflection and laser wavelength high reflectivity film system; the laser gain medium is coated with a pump light and laser wavelength antireflection film system; the cavity lens is coated with a laser wavelength antireflection film system; the first laser output mirror and the second laser output mirror are both plane mirrors, both of which are coated with a film system that allows partial transmission of laser wavelength on one side and a film system that increases laser wavelength on the other side. A higher-order Laguerre-Gaussian beam is focused by the cavity lens. Under the spherical aberration of the cavity lens, the beam waist of the focused beam will be separated. The higher the order of the mode and the larger the spot size, the closer the beam waist of the focused beam is to the cavity lens. Adjust the positions of the first and second laser output mirrors so that they are located at the waist position of a certain mode. The first and second laser output mirrors located at different positions provide feedback for two Laguerre-Gaussian vortex lights of different orders, so as to form multi-mode vortex laser oscillation and output. The first laser output mirror is arranged such that the side coated with the laser wavelength antireflection film faces into the laser resonant cavity composed of the gain medium and the intracavity lens. The second laser output mirror is arranged such that the side coated with the laser wavelength partial reflective film faces into the laser resonant cavity. When the generated vortex order is high, the aperture of the laser gain medium and the intracavity lens is larger than the size of the oscillating high-order vortex spot. , where w is the fundamental mode spot size determined by the ABCD matrix of the resonant cavity, and p and m are the radial and angular indices of the higher-order vortex light, respectively; The beam waist position of the higher-order Laguerre-Gaussian beam after focusing by the intracavity lens is given by the following formula: ； Where l' is the distance between the focused beam waist and the intracavity lens, l is the distance between the beam waist and the intracavity lens before focusing, f is the focal length of the intracavity lens, W is the spot size, λ is the laser wavelength, and p and m are the radial and angular indices of the Laguerre-Gaussian beam, respectively.

2. The order-tunable multimode vortex laser according to claim 1, characterized in that, The radius of curvature of the laser total reflection mirror is ≤100mm or a short focal length lens with a focal length ≤100mm is added nearby.

3. The order-tunable multimode vortex laser according to claim 1, characterized in that, The laser gain medium is: Nd:YVO4, Nd:YAG, Ti:Sa, or laser glass or laser ceramics doped with Nd, Yb, or Er.

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