CN116345286A - A multi-mode vortex laser with adjustable order - Google Patents

Abstract

The invention discloses a multi-mode vortex laser with adjustable order, which comprises: the intracavity lens is coated with a laser wavelength anti-reflection film system, the first laser output mirror and the second laser output mirror are both plane mirrors, and both are One side is coated with a film system that is partially transparent to the laser wavelength, and the other side is coated with a film system that is anti-reflective to the laser wavelength; the high-order Laguerre-Gaussian beam is focused by the cavity lens, and each order Laguerre-Gaussian mode Under the action of the spherical aberration of the intracavity lens, the vortex light will separate the beam waist after focusing, and the beam waist of the focused mode with the higher the mode order and the larger the spot size is closer to the intracavity lens; The positions of the first laser output mirror and the second laser output mirror are such that they are respectively located at the beam waist position of a certain mode, and the first laser output mirror and the second laser output mirror at different positions are respectively two different orders of laser output mirrors. Gail-Gaussian mode vortex light provides feedback to form multi-mode vortex laser oscillation and output.

Description

A multi-mode vortex laser with adjustable order

technical field

The invention relates to the field of lasers, in particular to an order-adjustable multi-mode vortex laser.

Background technique

的轨道角动量。对于拉盖尔-高斯(Laguerre-Gaussian)光束这种最为典型的涡旋光束而言，l就是其角向指数；由于涡旋光束中心存在相位奇点，其光强呈中空环状分布，相关特性使得涡旋光束在光镊、量子通信、微纳制造等方面具有重要应用。产生涡旋光束的方法包括无源和有源两大类，无源方法对既有的高斯光束或厄米高斯光束进行腔外调制和变换得到涡旋光，有源方法通过泵浦光整形和调整器/缺陷点尺寸和图样的设计加工来控制谐振腔内激光模式增益和损耗，从而实现模式选择、产生涡旋光振荡输出^[1]。The vortex beam has a spiral wavefront, and the phase of the wavefront changes by an integer multiple of 2π around the center, and each photon in the beam carries

orbital angular momentum of . For the Laguerre-Gaussian (Laguerre-Gaussian) beam, the most typical vortex beam, l is its angular index; since there is a phase singularity in the center of the vortex beam, its light intensity is distributed in a hollow ring, and the correlation characteristics The vortex beam has important applications in optical tweezers, quantum communication, and micro-nano manufacturing. There are two types of methods for generating vortex beams: passive and active. The passive method performs extracavity modulation and transformation on the existing Gaussian beam or Hermitian Gaussian beam to obtain vortex light. The active method uses pump light shaping and adjustment The gain and loss of the laser mode in the resonator is controlled by designing and processing the size and pattern of the device/defect point, so as to realize mode selection and generate vortex optical oscillation output ^[1] .

In applications such as quantum entanglement and space optical communication, it is often necessary to use vortex light sources containing multiple modes at the same time for multiplexing to improve system performance. However, the mode purity and power ratio of multimode beams are often difficult to control, and mode competition can also lead to fluctuations in light intensity, so a controllable multi-order vortex beam generation method is very important. Among the currently reported multi-mode vortex beam generation methods, only literature [2] proposes to control the order modes with different sizes by etching multiple concentric rings of different sizes on the mirror of the laser resonator. Loss, so as to achieve multi-mode vortex light output. However, the etching of patterns with complex structures on the cavity mirror requires high processing technology, and the device preparation is very difficult; The order of the mode can be adjusted flexibly and independently; moreover, the defect point is easily further damaged by the high-intensity laser in the cavity, so that the laser mode changes and even cannot continue to work. Therefore, it is difficult to realize multi-mode vortex light output with adjustable order in the prior art.

references

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

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

Contents of the invention

The invention provides a multi-mode vortex laser with adjustable order. The invention uses multiple laser output mirrors located at different positions to provide feedback to Laguerre-Gaussian mode vortex lasers of different orders to realize the order Adjustable multi-mode vortex laser oscillation output, see the description below for details:

A multi-mode vortex laser with adjustable order, said laser comprising:

The laser total reflection mirror is coated with pump light wavelength anti-reflection film system and laser wavelength high-reflection film system; the laser gain medium is coated with pump light and laser wavelength anti-reflection film system; the intracavity lens is coated with laser wavelength anti-reflection 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 partially transmits the laser wavelength on one side, and coated on the other side with a film system that is anti-reflective to the laser wavelength;

The high-order Laguerre-Gaussian beam is focused by the intracavity lens, and the vortex light of each order Laguerre-Gaussian mode will be separated under the spherical aberration of the intracavity lens, and the beam waist position after focusing will be separated. The higher the order and the larger the spot size, the closer the beam waist of the focused beam is to the intracavity lens;

Adjust the positions of the first laser output mirror and the second laser output mirror so that they are respectively located at the beam waist position of a certain mode, and the first laser output mirror and the second laser output mirror at different positions are respectively two different orders The Laguerre-Gaussian mode vortex light provides feedback to form multi-mode vortex laser oscillation and output.

Wherein, the arrangement direction of the first laser output mirror is: the side coated with the laser wavelength anti-reflection film system faces into the laser resonant cavity composed of the gain medium and the intracavity lens. The arrangement direction of the second laser output mirror is: the side coated with the film of the laser wavelength part faces into the laser resonant cavity.

其中w是由谐振腔ABCD矩阵决定的基模光斑尺寸，p和m分别为高阶涡旋光的径向和角向指数。Preferably, when the order of the generated vortex light is high, the clear aperture of the laser gain medium and the intracavity lens is larger than the size of the oscillating high-order vortex light spot

where w is the fundamental mode spot size determined by the ABCD matrix of the resonator, and p and m are the radial and angular indices of the higher-order vortex light, respectively.

Preferably, the radius of curvature of the laser total reflection mirror is ≤100mm, or a short focal length lens is added near it, and the focal length is ≤100mm.

The laser gain medium is: Nd:YVO ₄ , Nd:YAG, Ti:Sa, or Nd-doped, Yb-doped, Er-doped laser glass, laser ceramics.

The beneficial effects of the technical solution provided by the invention are:

1) The present invention uses two laser output mirrors located at different positions to provide feedback to different modes of vortex light respectively, thereby generating a multi-mode vortex laser output whose order can be easily adjusted, without the preparation and use of special devices, and the method is simple and convenient , cost economy;

2) The present invention utilizes a single pump light and a laser crystal to generate a multi-mode vortex laser, the structure is simple, and the spot sizes of the vortex lasers of different modes are different, so the gain areas are different, there is no gain competition, and it is more stable, and it is more stable for pumping High light utilization rate.

Description of drawings

Fig. 1 is a schematic diagram of the optical path of an order-tunable multi-mode vortex laser provided by the present invention;

Fig. 2 is a schematic diagram of the relationship between the beam focus position and the spot size under the action of spherical aberration in an embodiment of an order-adjustable multi-mode vortex laser provided by the present invention;

3 is a schematic diagram of the relationship between the order of the vortex light mode and the position of the laser output mirror in an embodiment of an order-tunable multi-mode vortex laser provided by the present invention.

In accompanying drawing 1, the parts list represented by each label is as follows:

1: pump source; 2: laser mirror;

3: laser gain medium; 4: intracavity lens;

5: the first laser output mirror; 6: the second laser output mirror.

Detailed ways

In order to make the purpose, technical solution and advantages of the present invention clearer, the implementation manners of the present invention will be further described in detail below.

Example 1

A multi-mode vortex laser with adjustable order, see Figure 1, the laser includes: pump source 1, laser total reflection mirror 2, laser gain medium 3, intracavity lens 4, first laser output mirror 5, second Two laser output mirrors 6 .

Among them, the laser total reflection mirror 2 is coated with a pump light wavelength antireflection film system and a laser wavelength high reflection film system; the laser gain medium 3 is coated with a pump light and laser wavelength antireflection film system; the intracavity lens 4 is coated with a laser wavelength enhancement film system. The transparent film system, the first laser output mirror 5 and the second laser output mirror 6 are both coated with a film system that partially transmits the laser wavelength on one side, and coated with an anti-reflection film system on the laser wavelength on the other side.

The distance between the laser total reflection mirror 2 and the intracavity lens 4 is relatively large, so the spot size is relatively large when the laser beam is transmitted to the intracavity lens 4; the first laser output mirror 5 and the second laser output mirror 6 are plane mirrors; the intracavity lens 4 is an ordinary spherical lens with spherical aberration.

Wherein, the beam waist position of the high-order Laguerre-Gaussian beam after being focused by the intracavity lens 4 is given by the following formula:

Among them, l' is the distance between the focused beam waist and the intracavity lens 4, l is the distance between the beam waist and the intracavity lens 4 before focusing, f is the focal length of the intracavity lens 4, W is the spot size, λ is the laser wavelength, p and m are the radial index and angular index of the Laguerre-Gaussian beam, respectively.

Since the Laguerre-Gaussian mode vortex light of each order has different beam sizes, under the action of the spherical aberration of the intracavity lens 4, the waist position of the focused beam will be separated, and the higher the mode order, the smaller the spot size. The beam waist of the focused large mode is closer to the intracavity lens 4 . Considering that both the first laser output mirror 5 and the second laser output mirror 6 are plane mirrors, according to the self-reproduction requirements of the laser resonator mode, only the mode whose beam waist is located on the plane mirror after being focused by the intracavity lens 4 can oscillate in the cavity , so the first laser output mirror 5 and the second laser output mirror 6 located at different positions can respectively provide feedback for two different orders of Laguerre-Gaussian mode vortex light, so that it forms a multi-mode vortex laser oscillation and outputs , and other modes are subject to greater loss and cannot start to vibrate. As long as the positions of the first laser output mirror 5 and the second laser output mirror 6 are adjusted so that they are located at the beam waist positions of a certain mode, the order of multi-mode vortex lasers can be individually tuned.

Among them, considering that the optical lens has a certain thickness, the preferred arrangement direction of the first laser output mirror 5 should be that the side coated with the laser wavelength anti-reflection coating system faces into the laser resonant cavity (that is, towards the gain medium 3 and the intracavity lens 4), The side with the laser wavelength part reflective film system faces out of the laser resonator (that is, towards the second laser output mirror 6); the preferred arrangement direction of the second laser output mirror 6 should be that the side coated with the laser wavelength part reflective film system faces the laser resonator Inside the cavity (towards the first laser output mirror 5). In this way, the distance between the partially reflective films used to provide feedback for different modes of vortex light can be adjusted within a large dynamic range, thereby adjusting the order of the multi-mode vortex light without being limited by the thickness of the lens.

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

Preferably, the laser total reflection mirror 2 should have a smaller radius of curvature (or add a short focal length lens near it), thereby compressing the laser beam waist size near it, so that the intracavity lens 4 has a larger spot size to Enhanced spherical aberration for better mode selection.

In summary, the embodiment of the present invention provides feedback to Laguerre-Gaussian mode vortex lasers of different orders through multiple laser output mirrors located at different positions, so as to realize the multi-mode vortex laser oscillation output with adjustable order , to meet a variety of needs in practical applications.

Example 2

An embodiment of the present invention provides an order-adjustable multi-mode vortex laser, which includes: a pump source 1, a laser total reflection mirror 2, a laser gain medium 3, an intracavity lens 4, and a first laser output mirror 5 , the second laser output mirror 6 .

Among them, the pump source 1 is an 808nm semiconductor laser; the laser total reflection mirror 2 is a plano-concave mirror, the radius of curvature of the concave surface is 50mm, facing the cavity, both sides are coated with an 808nm pump light anti-reflection film, and the concave surface is coated with a 1064nm laser high-reflection film system; Gain medium 3 is a-cut Nd:YVO ₄ crystal, 4×4×10mm ³ , doping concentration 0.3at.%, coated with 808nm pump light and 1064nm laser anti-reflection film system; intracavity lens 4 is a spherical surface made of K9 material Double convex lens, focal length 51.8mm, both coated with 1064nm laser anti-reflection film system; the first laser output mirror 5 and the second laser output mirror 6 are flat mirrors, respectively coated with 1064nm laser transmittance T = 5% and T = 10 % of the film system.

The laser total reflection mirror 2 is placed close to the laser gain medium 3; the distance between the intracavity lens 4 and the laser gain medium 3 is ~150 mm; the distance between the first laser output mirror 5 coated with a partially reflective film and the intracavity lens 4 50 mm, the position can be fine-tuned; the second laser output mirror 6 is placed close to the first laser output mirror 5, and the position can be fine-tuned.

In this case, by calculating the spherical aberration of the intracavity lens 4 and according to the above formula (1), the actual focus position after being focused by the intracavity lens 4 can be obtained, as shown in FIG. 2 . According to the calculation of the cavity mode theory, the spot size of the fundamental mode at the intracavity lens 4 is ~800 μm. According to the light field distribution of the Laguerre-Gaussian mode vortex light, the spot size of each order LG _0,m mode vortex light can be determined, and then according to The spherical aberration of the lens determines the relationship between the position of the laser output mirror relative to the intracavity lens and the corresponding oscillation mode, as shown in Figure 3. As long as the positions of the first laser output mirror 5 and the second laser output mirror 6 are finely adjusted, the corresponding multi-mode vortex laser output can be obtained.

In the above embodiments, the laser gain medium can be laser crystals such as Nd:YVO ₄ , Nd:YAG (neodymium-doped yttrium aluminum garnet), Ti:Sa (titanium-doped sapphire), or Nd-doped, Yb-doped (ytterbium) , laser glass doped with Er (erbium) or other luminescent ions, laser ceramics and other commonly used laser gain media, the corresponding pump source wavelength and coating wavelength can correspond to the absorption peak and emission peak of the laser gain medium. This is not limited.

The embodiment of the present invention does not specifically limit the focal length of the intracavity lens 4 , as long as an appropriate focal length is selected so that the beam is focused to produce obvious spherical aberration.

To sum up, the purpose of the embodiments of the present invention is to use spherical aberration to separate the optical paths of different modes of Laguerre-Gaussian mode vortex light in space, and use two laser output mirrors located at different positions to separate the optical paths of different orders of vortex light respectively. The vortex light provides feedback to realize multi-mode vortex laser oscillation output; by fine-tuning the position of the laser output mirror, the convenient adjustment of the order of the vortex light is realized.

In the embodiments of the present invention, unless otherwise specified, the models of the devices are not limited, as long as they can complete the above functions.

Those skilled in the art can understand that the accompanying drawing is only a schematic diagram of a preferred embodiment, and the serial numbers of the above-mentioned embodiments of the present invention are for description only, and do not represent the advantages and disadvantages of the embodiments.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection of the present invention. within range.

Claims (6)

1. An order tunable multimode vortex laser, the laser comprising:

the laser total reflection mirror is coated with a film system for increasing the reflection of the wavelength of pumping light and for reflecting the wavelength of laser light; the laser gain medium is coated with a pumping light and laser wavelength antireflection film system; the cavity lens is plated with a laser wavelength antireflection film system, the first laser output mirror and the second laser output mirror are plane mirrors, one surface of each mirror is plated with a film system which is partially transparent to the laser wavelength, and the other surface of each mirror is plated with a film system which is antireflection to the laser wavelength;

the high-order Laguerre-Gaussian beam is focused by the intracavity lens, the focused beam waist position can be separated under the spherical aberration action of the intracavity lens, and the focused beam waist of the mode with higher mode order and larger spot size is closer to the intracavity lens;

the positions of the first laser output mirror and the second laser output mirror are adjusted to be respectively positioned at the beam waist position of a certain mode, and the first laser output mirror and the second laser output mirror which are positioned at different positions respectively provide feedback for two Laguerre-Gaussian mode vortex lights with different orders so as to form multimode vortex laser oscillation and output.

2. The tunable multimode vortex laser of claim 1 wherein the first laser output mirror is arranged in a direction: one side coated with the laser wavelength antireflection film system faces into the laser resonant cavity formed by the gain medium and the intracavity lens.

3. The tunable multimode vortex laser of claim 2 wherein the second laser output mirror is arranged in a direction: the side coated with the laser wavelength part reflection film system faces into the laser resonant cavity.

4. The tunable multimode vortex laser of claim 2 wherein the clear aperture of the laser gain medium and the intracavity lens is greater than the size of the oscillating high order vortex light spot when the order of the vortex rotation generated is high

Where w is the fundamental mode spot size determined by the cavity ABCD matrix and p and m are the radial and angular indices, respectively, of higher order eddy current.

5. An order tunable multimode vortex laser according to claim 2 wherein the radius of curvature of the total laser reflection mirror is less than or equal to 100mm or a short focal length lens is added near the radius of curvature of the total laser reflection mirror, and the focal length is less than or equal to 100mm.

6. The tunable order multimode vortex laser of claim 1 wherein the laser gain medium is: nd YVO ₄ YAG, ti, sa, nd-doped, yb-doped and Er-doped laser glass and laser ceramics.

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