All-solid-state four-pass vortex-beam power amplifier

Abstract

The application discloses a kind of full solid four-way structure vortex light beam amplifier.The application is pumped by the design of shaping and four-way structure main oscillation power amplification optical path, and the mode matching of seed vortex light beam four times through gain crystal and after shaping annular pumping light beam, the power amplification of different order vortex light beam is realized.The application system structure is simple, and stability is strong, and power amplification ratio is significantly improved compared with straight-through structure vortex light beam main oscillation power amplification system, provides new light source scheme for the technical field of remote laser radar, laser processing and other vortex light beam power higher requirement.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of laser, and relates to a full-solid four-way structure vortex beam power amplifier. BACKGROUND

[0002] A vortex beam is a novel structured light field carrying orbital angular momentum (OAM), and its complex amplitude contains a spiral phase term (l is a topological charge value, is an angular coordinate), and each photon carries an OAM of ( is a reduced Planck constant), and l is also called the order of the vortex beam. The unique characteristics of the vortex beam make it have a wide application background in the fields of ultra-large-capacity optical communication, laser radar, optical micro-manipulation, high-dimensional information storage, quantum technology and other frontier technologies. At present, scholars at home and abroad have carried out a lot of research work on the generation technology of vortex beams, which can be mainly divided into two kinds of cavity-out mode conversion and cavity-in direct generation according to the generation method. However, due to the low damage threshold of the used modulation device, the current generated vortex beam has a small power, and the higher the order is, the lower the output power is, which to some extent limits the practical application of the vortex beam in the scene of long-distance laser radar, laser processing and other scenes requiring high laser power. Therefore, how to realize the power amplification of the vortex beam is one of the technical bottlenecks to be broken through at present. Master Oscillator Power Amplifier (MOPA) technology is a technology for injecting seed light into a gain medium under the action of pump light, so as to realize the power amplification of the seed light to generate high-power laser. The amplified laser has the same frequency and mode characteristics as the seed light. However, the existing MOPA technology is mostly used for power amplification of fundamental mode Gaussian beams, and often adopts a straight-through or double-pass structure, and there are problems such as great difficulty in mode matching, low energy extraction efficiency and the like for power amplification of structured light beams such as vortex beams with complex transverse mode distribution. In order to realize the power amplification of the vortex beam with a large magnification, a method of cascading multiple gain media and simultaneously acting by multiple pumps is often used, which has problems such as complex structure, high cost and the like. SUMMARY

[0003] In view of this, the application provides a full solid four-pass structure vortex beam power amplifier.A four-pass structure MOPA amplifier for vortex beam power amplification is ingeniously designed, a Faraday rotator and a polarization optical device are introduced, the injected seed vortex beam passes through a single gain medium under the action of pumping four times in succession, a conical lens and a collimating and expanding lens group are used to shape the pump beam, the mode matching between the seed vortex beam and the pump beam in the four-pass light path in the single gain medium is realized, and finally the high magnification power amplification of the seed vortex beam is realized.

[0004] The full solid four-pass structure vortex beam power amplifier provided by the application includes shaping of the pump light and amplification of vortex beams of different orders, the shaping of the pump beam is realized through a conical lens and a collimating and expanding lens group, the pump beam is matched with the seed vortex beam in mode, the energy extraction efficiency and the power amplification effect are as large as possible, the incident horizontally linearly polarized seed vortex beam to be amplified passes through a single gain medium four times through a Faraday rotator and a polarization optical device, and finally the vortex beam after power amplification is output.

[0005] The full solid four-pass structure vortex beam power amplifier provided by the application has a pump source, a collimating and expanding lens group, a conical lens, a seed vortex light source, two 45° dichroic mirrors, a gain medium, two polarization beam splitting prisms, a quarter-wave plate, a half-wave plate, a Faraday rotator and two mirrors.

[0006] The pump source is used to generate pump light and provide energy injection for the gain medium.

[0007] The expanding and collimating lens group is composed of two lenses and is arranged in the laser light path behind the pump source and is used to collimate and focus the pump beam on the center of the gain medium.

[0008] The conical lens is arranged in the laser light path between the two lenses of the collimating lens group and is used to shape the pump beam into a ring-shaped beam.

[0009] The seed vortex light source is used to generate vortex beams of different orders and provide seed vortex beams to be amplified for the amplifier.

[0010] The two 45° dichroic mirrors are placed at 45° and are both high-transmissive to the incident pump light and high-reflective to the seed vortex beam and the amplified light beam, the first 45° dichroic mirror is arranged in the pump laser light path behind the collimating and expanding lens group and is used to couple the pump light into the gain medium, and the second 45° dichroic mirror is arranged in the laser light path behind the gain medium and is used to couple the residual pump light after being absorbed by the gain medium out of the amplifier.

[0011] The gain medium is arranged in a laser light path between two 45-degree dichroic mirrors, for absorbing pump light energy and power amplifying the seed vortex light beam;

[0012] The two polarization beam splitting prisms are high-transmissive to horizontal linearly polarized light (p light) and high-reflective to vertical linearly polarized light (s light), for orthogonal polarization beam splitting, wherein the first polarization beam splitting prism is arranged in a laser light path behind the seed vortex light source, and the Faraday rotator and the half-wave plate together form an optical isolator, for transmitting the incident horizontal linearly polarized seed vortex light beam and reflecting the vortex light beam amplified four times through the gain medium; and the second polarization beam splitting prism is arranged in a laser light path behind the Faraday rotator and the half-wave plate, for transmitting the injected seed vortex light beam and the vortex light beam amplified four times through the gain medium, and reflecting the amplified light beam twice through the gain medium;

[0013] The Faraday rotator is arranged in a laser light path behind the first polarization beam splitting prism, for rotating the incident linearly polarized light 45 degrees clockwise;

[0014] The half-wave plate is arranged in a laser light path behind the Faraday rotator, with a fast axis placed at 22.5 degrees to the horizontal plane, and cooperates with the Faraday rotator to keep the horizontal linearly polarized light unchanged when the light is incident in a forward direction, and to convert the horizontal linearly polarized light into vertical linearly polarized light when the light is incident in a reverse direction;

[0015] The quarter-wave plate is arranged in a laser light path reflected by the second 45-degree dichroic mirror, with a fast axis placed at 45 degrees to the horizontal plane, for changing the polarization state of the incident light after returning;

[0016] The two mirrors are both high-reflective to the amplified vortex light beam, the first mirror is arranged in a laser light path behind the quarter-wave plate, for reflecting the one-pass and three-pass amplified vortex light beams, and the second mirror is arranged in a laser light path behind the reflection of the second polarization beam splitting prism, for reflecting the two-pass amplified vortex light beam.

[0017] The present application has the following beneficial effects:

[0018] (1) The seed vortex light beam passes through the gain medium four times through the design of the four-pass structure, effectively improving the energy extraction efficiency, and realizing power amplification of different order small power vortex light beams;

[0019] (2) The system structure is simple, the cost is low, the overall system has strong adaptability and high flexibility, and provides a technical solution for generating high-power high-order vortex light beams. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1This is a schematic diagram of the all-solid-state four-way vortex beam power amplifier provided by the present invention, wherein: 1 is a pump source; 2 and 3 are lenses, which together constitute a collimating and beam-expanding lens group; 4 is a conical lens; 5 and 6 are 45° dichroic mirrors; 7 is a gain medium; 8 is a seed vortex light source; 9 and 10 are polarizing beam splitters; 11 is a Faraday rotator; 12 is a half-wave plate; 13 is a quarter-wave plate; and 14 and 15 are reflecting mirrors.

[0021] Figure 2 To utilize the all-solid-state four-channel vortex beam power amplifier of the present invention to amplify the output power curves of 1645nm vortex beams of different orders, where: the horizontal axis represents the pump light power, the vertical axis represents the amplified vortex beam power, and the upper right corner represents the intensity distribution of the amplified vortex beam. Detailed Implementation

[0022] The following detailed explanation is provided with specific examples and accompanying diagrams.

[0023] The present invention discloses an all-solid-state four-way vortex beam amplifier, the structural diagram of which is shown below. Figure 1 As shown: It includes a pump source (1), a collimating and beam-expanding lens group (2, 3), a conical lens (4), two 45° dichroic mirrors (5, 6), a gain medium (7), a seed vortex light source (8), a polarizing beam splitter (9, 10), a Faraday rotator (11), a half-wave plate (12), a quarter-wave plate (13), and a reflecting mirror (14, 15). Among them:

[0024] The pump source (1) is used to generate pump light to provide energy injection for the gain medium (7); the beam expanding collimating lens group (2, 3) is placed in the laser light path behind the pump source, and is used to collimate and focus the pump light beam to the center of the gain medium; the conical lens (4) is placed in the collimated pump light path behind the lens (2) of the collimating lens group, and is used to shape the pump light beam into a ring-shaped beam; the seed vortex light source (8) is used to generate various vortex beams of different orders, and provides seed vortex beams to be amplified for the amplifier; the two 45° dichroic mirrors (5, 6) are placed at 45°, and they have high transmission to the incident pump light and high reflection to the seed vortex light beam and the amplified light beam, wherein the first 45° dichroic mirror (5) is placed in the pump laser light path behind the collimating and expanding lens group, and is used to couple the pump light into the gain medium; the second 45° dichroic mirror (6) is placed in the laser light path behind the gain medium, and is used to couple the residual pump light absorbed by the gain medium out of the amplifier; the gain medium (7) is placed in the laser light path between the two 45° dichroic mirrors (5, 6), and is used to absorb the pump light energy and amplify the power of the seed vortex light beam; the two polarization beam splitting prisms (9, 10) have high transmission to the horizontally polarized light (p light) and high reflection to the vertically polarized light (s light), and are used for orthogonal polarization splitting, wherein the first polarization beam splitting prism (9) is placed in the laser light path behind the seed vortex light source, and together with the Faraday rotator (11) and the half-wave plate (12), forms an optical isolator, which is used to transmit the incident horizontally polarized seed vortex light beam and reflect the vortex light beam amplified four times through the gain medium; the second polarization beam splitting prism (10) is placed in the laser light path behind the Faraday rotator (11) and the half-wave plate (12), and is used to transmit the injected seed vortex light beam and the vortex light beam amplified four times through the gain medium, and reflect the amplified light beam twice through the gain medium; the Faraday rotator (11) is placed in the laser light path behind the first polarization beam splitting prism (9), and is used to rotate the incident linearly polarized light 45° clockwise; the half-wave plate (12) is placed in the laser light path behind the Faraday rotator (11), and its fast axis is placed at 22.5° to the horizontal plane, and together with the Faraday rotator (11), it is used to keep the polarization of the forward incident horizontally polarized light unchanged, and to convert the backward incident horizontally polarized light into vertically polarized light; the quarter-wave plate (13) is placed in the reflected laser light path of the second 45° dichroic mirror (6), and its fast axis is placed at 45° to the horizontal plane, and is used to change the polarization state of the returned incident light; the two mirrors (14, 15) both have high reflection to the amplified vortex light beam, the first mirror (14) is placed in the laser light path behind the quarter-wave plate (13), and is used to reflect the one-pass and three-pass amplified vortex light beams, and the second mirror (15) is placed in the laser light path behind the reflection of the second polarization beam splitting prism (10), and is used to reflect the two-pass amplified vortex light beam.

[0025] The working process and principle of the full solid four-pass structure vortex beam power amplifier are as follows:

[0026] The pump source (1) generates a pump beam, which becomes a ring-shaped beam after passing through the beam expansion collimation lens group (2, 3) and the conical lens (4), is coupled into the amplifier by the 45° dichroic mirror (5), is focused in the gain medium (7), and the spot size of the ring-shaped beam after the pump light shaping can be changed by adjusting the position of the conical lens, so that the best mode matching with the seed vortex beam to be amplified is achieved. The gain medium (7) absorbs the pump beam, so that the power amplification of the seed vortex beam is realized, and the residual part of the pump light is transmitted and coupled out of the amplifier by the second 45° dichroic mirror (6), and the seed vortex beam and the amplified vortex beam are reflected on the 45° dichroic mirror (5, 6). The seed vortex light source (8) can provide vortex beams of different orders of horizontal linear polarization, and after passing through the polarization beam splitter prism (9), the Faraday rotator (11) and the half-wave plate (12) in turn, the polarization state remains unchanged, and then after being transmitted by the polarization beam splitter prism (10), it is reflected by the first 45° dichroic mirror (5) and then enters the gain medium (3), is aligned with the ring-shaped pump beam and is mode matched, so that the first power amplification (one-pass amplification) is realized. The horizontal linear polarization vortex beam after one-pass amplification is reflected by the second 45° dichroic mirror (6), passes through the quarter-wave plate (13) placed at 45° with the horizontal plane, is reflected by the mirror (14), and then, after passing through the quarter-wave plate (13) again, it is converted into a vertical linear polarization vortex beam and is subjected to the second power amplification (two-pass amplification) by passing through the gain medium (3) for the second time. The vertical polarization vortex beam after two-pass amplification is reflected by the 45° dichroic mirror (5) and then reflected by the polarization beam splitter prism (10) to the mirror (15), and then reflected by the mirror (15), returns to the gain medium along the same optical path, and realizes the third power amplification (three-pass amplification). The vertical polarization vortex beam after three-pass amplification is reflected by the mirror (14) after passing through the quarter-wave plate (13), and then converted into a horizontal linear polarization vortex beam by passing through the quarter-wave plate (13) again, reflected by the 45° dichroic mirror (6), and subjected to the fourth power amplification (four-pass amplification) by passing through the gain medium for the fourth time. The horizontal linear polarization vortex beam after four-pass amplification is reflected by the 45° dichroic mirror (5), is transmitted by the polarization beam splitter prism (10), and then is converted into a vertical linear polarization by passing through the half-wave plate (12) and the Faraday rotator (11), is reflected by the polarization beam splitter prism (9), and then is output from the amplifier, thereby completing the entire four-pass structure power amplification process.

[0027] As described above, the seed vortex beams of various orders can be mode matched with the shaped ring-shaped pump light by adjusting the conical lens, and the final four-pass power amplification is realized by using the special four-pass structure designed according to the orthogonal polarization characteristics.

[0028] The actual performance of the all-solid-state four-pass structure vortex beam power amplifier is introduced below in combination with the embodiments.

[0029] Example: All-solid-state 1645 nm vortex-beam power amplifier with a four-pass configuration

[0030] In the embodiment, a third-order vortex beam of 1645 nm is used as a seed vortex light source, a 1532 nm fiber laser is used as a pump source, and an Er:YAG crystal is used as a gain medium, and finally a high-gain power amplified vortex beam of the same order of 1645 nm is generated at the output end of the amplifier. The experimental results are shown in Figure 2 Fig. (a) is the far-field diffraction intensity distribution of the third-order vortex beam before and after power amplification, and the right column is the far-field diffraction intensity distribution after the tilt lens; (b) is the power amplification characteristic curve of the third-order vortex beam, the horizontal coordinate is the pump source power, and the vertical coordinate is the power of the amplified third-order vortex beam. Figure 2 It is shown that the all-solid-state four-pass structure vortex beam amplifier of the present application successfully realizes high-gain power amplification of the vortex beam.

[0031] It should be noted that the all-solid-state four-pass structure vortex beam amplifier of the present application is not limited to the devices in the embodiments, and is not restricted by the selection of the pump source, the seed vortex light source, the gain medium, etc.

[0032] In summary, the above is only a preferred embodiment of the present application, and is not used to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A fully solid-state four-way vortex beam power amplifier, comprising a pump source, a collimating and expanding lens group, a conical lens, a seed vortex source, two 45° dichroic mirrors, a gain medium, two polarizing beam splitters, a quarter-wave plate, a half-wave plate, a Faraday rotator, and two reflecting mirrors, wherein: The pump source is used to generate pump light to provide energy injection to the gain medium; The collimating and beam expanding lens group consists of two lenses and is placed in the laser optical path behind the pump source to collimate and focus the pump beam into the gain medium. The conical lens is placed in the laser optical path between the two lenses of the collimating lens group. It is used to shape the pump beam into a ring beam. By adjusting the front and rear positions of the conical lens, the size of the ring beam spot is changed, ensuring the optimal mode matching between the ring pump beam and the seed vortex beam in the four-way gain medium. The seed vortex light source is used to generate vortex beams of different orders to be amplified. The two 45° dichroic mirrors are placed at a 45° angle. Both are highly transparent to the incident pump light and highly reflective to the seed vortex beam and the amplified beam. The first 45° dichroic mirror is placed in the laser optical path behind the collimating and expanding lens group to couple the pump light into the gain medium. The second 45° dichroic mirror is placed in the laser optical path behind the gain medium to couple the residual pump light after absorption by the gain medium out of the amplifier. The gain medium is placed in the laser optical path behind the first 45° dichroic mirror to absorb pump light energy and amplify the power of the seed vortex beam. The two polarizing beam splitters are highly transparent to horizontally linearly polarized beams (p-beams) and highly reflective to vertically linearly polarized beams (s-beams), and are used for orthogonal polarization beam splitting. The first polarizing beam splitter is placed in the laser optical path behind the seed vortex source, and together with the Faraday rotator and the half-wave plate, it forms an optical isolator, used to transmit the incident horizontally linearly polarized seed vortex beam and reflect the vortex beam amplified four times through the gain medium. The second polarizing beam splitter is placed in the laser optical path behind the Faraday rotator and the half-wave plate, used to transmit the injected seed vortex beam and the vortex beam amplified four times through the gain medium, and reflect the amplified beam after passing through the gain medium twice. The Faraday rotator is placed in the laser optical path behind the first polarizing beam splitter and is used to rotate the incident ray-polarized light 45° clockwise. The half-wave plate is placed in the laser optical path behind the Faraday rotator, with its fast axis at 22.5° to the horizontal plane. It works together with the Faraday rotator to keep the polarization of the forward-incident horizontal linearly polarized light unchanged, while converting the reverse-incident horizontal linearly polarized light into vertically polarized light. The quarter-wave plate is placed in the reflected laser path of the second 45° dichroic mirror, with its fast axis at 45° to the horizontal plane, to change the polarization state of the incident light after it returns. Both mirrors are highly reflective of the amplified vortex beam. The first mirror is placed in the laser path behind the quarter-wave plate to reflect the one-pass and three-pass amplified vortex beams. The second mirror is placed in the laser path behind the reflection of the second polarizing beam splitter to reflect the two-pass amplified vortex beam.

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