A device for controlling the polarization of a light beam, a thermal depolarization compensation system, and a method of use

Abstract

The present invention relates to a device for controlling the polarization of a light beam, a thermal depolarization compensation system and a usage method, belonging to the technical field of thermal depolarization compensation. The depolarization of the light beam has a certain spatial distribution. First, a wavefront sensor is used to measure the spatial distribution of the phase difference between the ordinary light and the extraordinary light. Then, an electric field with the required spatial distribution is loaded on the device for controlling the polarization of the light beam, and corresponding birefringence will be generated at different positions in the electro-optic crystal. When the light beam passes through, the phase difference between the ordinary light and the extraordinary light will be corrected, thereby realizing the adaptive compensation of thermal depolarization. Compared with the traditional static thermal depolarization compensation system, the present invention can perform active programming control according to the spatial distribution of the thermal depolarization of the light beam, realize the closed-loop active compensation of the thermal depolarization of the light beam, can effectively improve the compensation effect of thermal depolarization and the adaptability of depolarization compensation under complex thermal depolarization distributions, and further improve the flexibility of the optical path design of the laser system.

Description

Technical Field

[0001] The present invention belongs to the technical field of thermal depolarization compensation, and specifically relates to a beam polarization controllable device, a thermal depolarization compensation system and a usage method. Background Art

[0002] Driven by demands such as laser particle acceleration and material surface treatment, the high-power laser to achieve high-repetition-rate operation has become the mainstream trend of the development of high-power lasers. High-repetition-rate operation means high average power. A series of thermal effects caused by internal heat deposition in the gain medium severely restrict the improvement of the laser operation frequency. In a laser, after the pump source pumps the gain medium, a part of the pump energy is deposited in the gain medium in the form of heat energy. The non-uniformity of heat conduction and surface cooling of the medium leads to the generation of temperature gradient and thermal stress distribution in the gain medium. Under the action of thermo-optic effect, elasto-optic effect, etc., a series of thermal effect problems will occur when the beam passes through the gain medium. Among them, thermal depolarization and thermally induced wavefront distortion are the main manifestations of the thermal effects of the laser system. There are already mature adaptive active correction technologies to eliminate the influence of wavefront distortion on the quality of the laser beam (Feature issue introduction: application of adaptive optics, 《Optics Express》, 29, 2021, 11533-11537). Thermal depolarization changes the polarization state of the beam from linearly polarized light to elliptically polarized light. After passing through the polarization analyzer device, the uniformity of the near-field distribution of the beam becomes worse, and the depolarized part of the beam will deflect out of the optical path, thus increasing the insertion loss of the system.

[0003] At present, the main means of controlling thermal depolarization is to improve the uniformity of the temperature distribution in the gain medium to reduce thermal depolarization. On this basis, devices such as 90° rotors, Faraday, half-wave plates, and conical prisms are used to achieve the compensation of thermal depolarization (Peculiarity of the thermally induced depolarization and methods of depolarization compensation in square-shaped Yb:YAG active elements, 《Optics Communications》, 402, 2017, 468 - 471). In a small-aperture and low-average-power laser system, passive thermal depolarization compensation methods can usually compensate for thermal depolarization relatively well, but their adaptability and the flexibility of the optical path design are poor. Commercial liquid crystal light modulators have a spatial programmable function. The literature (Compensation for laser beam depolarization by spatial light modulations, 《radiophysics and quantum electronics》, 61(2), 2019, 924 - 929) reported depolarization measurement and active compensation methods based on such devices. However, the laser damage threshold of liquid crystal light modulators is low and the clear aperture is small, and they can only be used in laser amplifiers with a laser energy flux less than 300 mJ / cm 2 ² and a beam aperture in the centimeter range. In recent years, with the increase in the output energy, the expansion of the beam aperture, and the improvement of the average power of high-power repetitive-pulse laser systems, the problems of traditional thermal depolarization compensation systems and their usage methods in terms of compensation effect, adaptability, and the flexibility of the optical path design have become increasingly prominent, severely restricting the improvement of the high-power operating frequency. Summary of the Invention

[0004] In view of the various deficiencies of the prior art and to solve the above problems, a beam polarization controllable device, a thermal depolarization compensation system, and a usage method are proposed.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] In the first aspect, the present invention provides a beam polarization controllable device, including a main body. Inside the main body, there are successively provided an optical window, a discharge chamber, an electro-optic crystal, and a high-reflection mirror from front to back. The front surface of the high-reflection mirror is coated with a high-reflection film, and the rear surface of the high-reflection mirror is coated with a gold film grating. The discharge chamber and the gold film grating are respectively electrically connected to a pulsed power supply, and the pulsed voltage values applied by the pulsed power supply to different positions of the gold film grating are different.

[0007] This technical solution is further configured such that the gold film grating is composed of multiple grid-shaped sub-regions, and each sub-region is electrically connected to the pulse power supply respectively.

[0008] This technical solution is further configured such that the discharge chamber is filled with a He-Ne mixed gas, and an air extraction nozzle and a discharge needle are provided in the discharge chamber.

[0009] This technical solution is further configured such that the high-voltage end of the pulse power supply is electrically connected to the gold film grating through a high-voltage cable, and the grounding end of the pulse power supply is electrically connected to the discharge needle through a grounding wire.

[0010] This technical solution is further configured such that there is a gap between the electro-optic crystal and the high-reflection mirror, and the gap is filled with a He-Ne mixed gas.

[0011] In a second aspect, the present invention provides a thermal depolarization compensation system, including:

[0012] A sampling mirror, which is located on the optical path of the beam transmission and divides the beam into a sampling beam and a main beam;

[0013] A polarizer, which is located on the optical path of the sampling beam and divides the sampling beam into a P-polarized beam and an S-polarized beam;

[0014] A wavefront sensor, which is respectively located on the optical paths of the P-polarized beam and the S-polarized beam and is communicatively connected to a processor;

[0015] And a beam polarization controllable device, which is located on the optical path of the main beam and is connected to the pulse power supply, and the pulse power supply is communicatively connected to the processor.

[0016] This technical solution is further configured such that the main beam enters the interior of the beam polarization controllable device through an optical window and is reflected by the high-reflection mirror to output from the beam polarization controllable device, and the pulse power supply is communicatively connected to the processor.

[0017] In a third aspect, the present invention further provides a method for using a thermal depolarization compensation system, including the following steps:

[0018] Dividing the incident beam into a sampling beam and a main beam, measuring the phase space distributions of the P-polarized beam and the S-polarized beam in the sampling beam, and obtaining the phase difference space distribution of the P-polarized beam and the S-polarized beam;

[0019] According to the phase difference space distribution of the P-polarized beam and the S-polarized beam, the pulse power supply outputs different pulse voltage values and loads them onto the beam polarization controllable device. The main beam enters the beam polarization controllable device, and the electro-optic crystal corrects the phase difference between the ordinary light and the extraordinary light of the main beam. The polarization state of the output beam reflected by the beam polarization controllable device becomes linearly polarized light, realizing thermal depolarization compensation.

[0020] This technical solution is further configured such that the incident light beam is divided into a sampling light beam and a main light beam after passing through the sampling mirror. The sampling light beam is divided into a P-polarized light beam and an S-polarized light beam after passing through the polarizer. The phase space distributions of the P-polarized light beam and the S-polarized light beam are respectively measured by the wavefront sensor, and the measured phase space distribution data is input into the processor to calculate the phase difference space distribution of the P-polarized light beam and the S-polarized light beam.

[0021] This technical solution is further configured such that, according to the phase difference space distribution of the P-polarized light beam and the S-polarized light beam, the processor calculates the pulse voltage values required to be loaded on different sub-regions of the gold film grating. The pulse power supply outputs different pulse voltage values and loads them onto the gold film grating. Utilizing the electro-optic effect of the electro-optic crystal, the required birefringence is generated at different positions of the electro-optic crystal. The main light beam is incident on the electro-optic crystal through the light window and the discharge chamber, and the electro-optic crystal corrects the phase difference between the ordinary light and the extraordinary light of the main light beam. The polarization state of the output light beam reflected by the high-reflection mirror becomes linearly polarized light.

[0022] The beneficial effects of the present invention are as follows:

[0023] 1. The discharge chamber generates plasma as the incident-side electrode through the discharge of the mixed gas, which has the characteristics of optical transparency, high conductivity, and high laser damage threshold, and can withstand high laser fluxes.

[0024] 2. The high-reflection mirror uses a non-metallic material as the substrate, and the high-reflection film and the gold film grating are plated on different surfaces. The light beam is reflected by the front surface of the high-reflection mirror, avoiding the light beam transmitting to the gold film grating electrode on the rear surface of the high-reflection mirror, and can be used under high-throughput conditions.

[0025] 3. The forward discharge chamber can generate a large-area uniform plasma electrode, and the light-transmitting aperture can be scaled up.

[0026] 4. The beam polarization control device can be used in various lasers with a laser energy flux of several J / cm 2 and a light-transmitting aperture of dozens of cm to compensate for the laser thermal depolarization effect.

[0027] 5. Realize closed-loop active compensation for beam thermal depolarization, which can effectively improve the compensation effect of thermal depolarization and the adaptability of depolarization compensation under complex thermal depolarization distributions, and further improve the flexibility of the optical path design of the laser system. Description of the Drawings

[0028] Figure 1 is a schematic diagram of the beam polarization control device in the present invention;

[0029] Figure 2 is a schematic diagram of the thermal depolarization compensation system in the present invention;

[0030] Figure 3It is a flowchart of the usage method of the thermal depolarization compensation system in the present invention.

[0031] In the attached drawings: 100 - main body, 200 - optical window, 300 - discharge chamber, 400 - electro-optic crystal, 500 - high-reflection mirror, 600 - pulse power supply, 700 - high-voltage beam line, 800 - grounding wire;

[0032] 1 - laser, 2 - incident beam, 3 - sampling mirror, 4 - polarizer, 5 - first wavefront sensor, 6 - second wavefront sensor, 7 - processor, 8 - beam polarization controllable device, 9 - output beam. Specific embodiments

[0033] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be clearly and completely described below in conjunction with the attached drawings of the present invention. Based on the embodiments in this application, other similar embodiments obtained by those of ordinary skill in the art without creative efforts shall all fall within the scope of protection of this application. In addition, the directional terms mentioned in the following embodiments, such as "up", "down", "left", "right", etc., are only with reference to the direction of the attached drawings. Therefore, the directional terms used are for illustration rather than to limit the present invention.

[0034] Embodiment 1:

[0035] As Figure 1 shown, a beam polarization controllable device includes a main body 100. Inside the main body 100, an optical window 200, a discharge chamber 300, an electro-optic crystal 400, and a high-reflection mirror 500 are sequentially arranged from front to back. The front surface of the high-reflection mirror 500 is coated with a high-reflection film, and the back surface of the high-reflection mirror 500 is coated with a gold film grating. The discharge chamber 300 and the gold film grating are respectively electrically connected to a pulse power supply 600, and the pulse voltage values applied by the pulse power supply 600 to different positions of the gold film grating are different.

[0036] This technical solution is further arranged such that the gold film grating is composed of a plurality of grid-shaped sub-regions, and each sub-region is respectively electrically connected to the pulse power supply 600.

[0037] It should be noted that the high-voltage end of the pulse power supply 600 is electrically connected to the gold film grating through a high-voltage beam line 700. Among them, the pulse power supply 600 can output multiple paths of pulse voltage, and the sub-regions are arranged one-to-one with the high-voltage beam line 700.

[0038] This technical solution is further arranged such that the discharge chamber 300 is filled with a He and Ne mixed gas, and the discharge chamber 300 is provided with an air extraction nozzle and a discharge needle.

[0039] It should be noted that the degree of vacuum in the discharge chamber 300 is adjusted to the required level through the air extraction nozzle. The discharge chamber 300 generates plasma through the discharge of a mixed gas and serves as the incident-side electrode. It is optically transparent, has high electrical conductivity, and a high laser damage threshold, and can withstand a high laser flux.

[0040] This technical solution is further configured such that the grounding terminal of the pulse power supply 600 is electrically connected to the discharge needle through a grounding wire 800.

[0041] It should be noted that the plasma electrode generated by the discharge chamber 300 is grounded as a whole and has the same potential. Different sub-regions can be loaded with pulse voltages of different amplitudes as needed. Therefore, the electric fields at different positions of the electro-optic crystal 400 are different, and different birefringences are generated accordingly.

[0042] This technical solution is further configured such that there is a gap between the electro-optic crystal 400 and the high-reflection mirror 500, and the gap is filled with a He-Ne mixed gas.

[0043] It should be noted that the conduction heat transfer between the electro-optic crystal 400 and the high-reflection mirror 500 is achieved through the mixed gas in the gap. The high-reflection mirror 500 with high thermal conductivity can conductively cool the electro-optic crystal 400 longitudinally. At the same time, it avoids the damage of the anti-reflection film layer of the electro-optic crystal 400 and the clamping stress caused by direct contact sealing, and reduces the stress accumulation caused by the limited thermal expansion of the electro-optic crystal 400. At the same time, the high-reflection mirror 500 uses a non-metallic material as the substrate, and the high-reflection film and the gold film grating are plated on different surfaces. The light beam is reflected by the front surface of the high-reflection mirror 500, avoiding the light beam transmitting to the gold film grating electrode on the back surface of the high-reflection mirror 500, so that the light beam polarization control device can operate at a high flux.

[0044] In summary, the laser incident-side electrode is a transparent plasma, the back-side electrode is a gold film grating plated on the back surface of the high-reflection mirror 500, and the uniformity of the electric field distribution in the electro-optic crystal 400 is not limited by the light-transmitting aperture. At the same time, the cooling method is longitudinal conduction cooling, and the heat is transferred longitudinally, and the heat transfer efficiency is not limited by the transverse light-transmitting aperture. Therefore, the light-transmitting aperture of the light beam polarization control device is not affected by factors such as electric field uniformity and heat transfer efficiency, and has the characteristic of scalable magnification of the aperture. Specifically, its light-transmitting aperture is dozens of cm, and it can be used in various lasers with a laser energy flux of several J / cm 2 to compensate for the laser thermal depolarization effect.

[0045] Embodiment 2:

[0046] As Figure 1 and Figure 2 shown, a thermal depolarization compensation system includes:

[0047] Sampling mirror 3, the laser 1 outputs a light beam, the sampling mirror 3 is located on the light beam transmission optical path, and divides the light beam into a sampling light beam and a main light beam;

[0048] Polarizer 4, which is located on the transmission optical path of the sampling light beam, and divides the sampling light beam into a P-polarized light beam and an S-polarized light beam;

[0049] Wavefront sensor, which is respectively located on the transmission optical paths of the P-polarized light beam and the S-polarized light beam, and is communicatively connected to the processor 7;

[0050] And a light beam polarization controllable device 8, which is located on the transmission optical path of the main light beam and is connected to a pulse power supply, and the pulse power supply is communicatively connected to the processor 7.

[0051] This technical solution is further configured that the light beam polarization controllable device 8 includes a main body 100. Inside the main body 100, there are successively arranged a light window 200, a discharge chamber 300, an electro-optic crystal 400, and a high-reflection mirror 500 from front to back. The discharge chamber 300 and the gold film grating are respectively electrically connected to the pulse power supply 600. The main light beam is incident into the interior of the light beam polarization controllable device through the light window 200, and is reflected by the high-reflection mirror 500 to output the light beam polarization controllable device 8. The pulse power supply 600 is communicatively connected to the processor 7.

[0052] This technical solution is further configured that the wavefront sensor includes a first wavefront sensor 5 and a second wavefront sensor 6. Specifically, the first wavefront sensor 5 is located on the transmission optical path of the P-polarized light beam and is used to measure the phase space distribution of the P-polarized light beam. The second wavefront sensor 6 is on the transmission optical path of the S-polarized light beam and is used to measure the phase space distribution of the S-polarized light beam.

[0053] Embodiment 3:

[0054] As Figures 1 to 3 shown, a method for using a thermal depolarization compensation system includes the following steps:

[0055] Divide the incident light beam 2 into a sampling light beam and a main light beam, measure the phase space distribution of the P-polarized light beam and the S-polarized light beam in the sampling light beam, and obtain the phase difference space distribution of the P-polarized light beam and the S-polarized light beam;

[0056] According to the phase difference space distribution of the P-polarized light beam and the S-polarized light beam, the pulse power supply 600 outputs different pulse voltage values and loads them onto the light beam polarization controllable device 8. The main light beam is incident into the light beam polarization controllable device 8, and the electro-optic crystal 400 corrects the phase difference between the ordinary light and the extraordinary light of the main light beam. The polarization state of the output light beam 9 reflected by the light beam polarization controllable device 8 becomes linearly polarized light, realizing thermal depolarization compensation.

[0057] This technical solution is further configured such that the incident light beam 2 is divided into a sampling light beam and a main light beam after passing through the sampling mirror 3. The sampling light beam is divided into a P-polarized light beam and an S-polarized light beam after passing through the polarizer 4. The phase space distribution of the P-polarized light beam is measured by the first wavefront sensor 5, and the phase space distribution of the S-polarized light beam is measured by the second wavefront sensor 6. The measured phase space distribution data is input into the processor 7, and the phase difference space distribution of the P-polarized light beam and the S-polarized light beam is calculated.

[0058] This technical solution is further configured such that, according to the phase difference space distribution of the P-polarized light beam and the S-polarized light beam, the processor 7 calculates the pulse voltage values required to be loaded on different sub-regions of the gold film grating. The processor 7 controls the pulse power supply 600 to output different pulse voltage values and load them onto the gold film grating. Utilizing the electro-optic effect of the electro-optic crystal 400, the required birefringence is generated at different positions of the electro-optic crystal 400. The main light beam is incident on the electro-optic crystal 400 through the optical window 200 and the discharge chamber 300. The electro-optic crystal 400 corrects the phase difference between the ordinary light and the extraordinary light of the main light beam, and the polarization state of the output light beam 9 reflected by the high reflector 500 becomes linearly polarized light.

[0059] It should be noted that the thermal depolarization of the light beam has a certain spatial distribution (the thermal depolarization at different positions of the light beam is different). First, the wavefront sensor is used to measure the spatial distribution of the phase difference between the ordinary light and the extraordinary light, and then an electric field with the required spatial distribution is loaded on the light beam polarization control device 8. Corresponding birefringence will be generated at different positions within the electro-optic crystal 400, and the phase difference between the ordinary light and the extraordinary light will be corrected when the light beam passes through, thereby achieving adaptive compensation for thermal depolarization. Compared with the traditional static thermal depolarization compensation system, the present invention can perform active programming control according to the spatial distribution of the light beam thermal depolarization, realize closed-loop active compensation for the light beam thermal depolarization, effectively improve the compensation effect of thermal depolarization and the adaptability of depolarization compensation under complex thermal depolarization distributions, and further improve the flexibility of the optical path design of the laser system.

[0060] The present invention has been described in detail above. The above description is only a preferred embodiment of the present invention, and it cannot limit the scope of implementation of the present invention. That is, all equivalent changes and modifications made according to the scope of this application should still fall within the scope covered by the present invention.

Claims

1. A device for controlling the polarization of a light beam, characterized in that It includes a main body, inside which there are successively arranged a light window, a discharge chamber, an electro-optic crystal and a high-reflection mirror from front to back. A high-reflection film is plated on the front surface of the high-reflection mirror, and a gold film grating is plated on the back surface of the high-reflection mirror. The discharge chamber and the gold film grating are respectively electrically connected to a pulse power supply, and the pulse voltage values applied by the pulse power supply to different positions of the gold film grating are different.

2. The beam polarization controllable device according to claim 1, characterized in that, The gold film grating is composed of a plurality of grid-shaped sub-regions, and each sub-region is respectively electrically connected to the pulse power supply.

3. A beam polarization controllable device according to claim 1, characterized in that, The discharge chamber is filled with a He-Ne mixed gas, and an air extraction nozzle and a discharge needle are provided in the discharge chamber.

4. The beam polarization controllable device according to claim 3, characterized in that, The high-voltage end of the pulse power supply is electrically connected to the gold film grating through a high-voltage cable, and the grounded end of the pulse power supply is electrically connected to the discharge needle through a grounding wire.

5. A beam polarization controllable device according to claim 1, characterized in that There is a gap between the electro-optic crystal and the high-reflection mirror, and the gap is filled with a He-Ne mixed gas.

6. A thermal depolarization compensation system, characterized in that, It includes: A sampling mirror, which is located on the optical path of the beam transmission and divides the beam into a sampling beam and a main beam; A polarizer, which is located on the optical path of the sampling beam and divides the sampling beam into a P-polarized beam and an S-polarized beam; A wavefront sensor, which is respectively located on the optical paths of the P-polarized beam and the S-polarized beam and is communicatively connected to a processor; And a beam polarization controllable device according to any one of claims 1-5, which is located on the optical path of the main beam and is connected to a pulse power supply, and the pulse power supply is communicatively connected to the processor.

7. The thermal depolarization compensation system according to claim 6, wherein The main beam is incident into the beam polarization controllable device through the light window, and is reflected by the high-reflection mirror to output from the beam polarization controllable device. The pulse power supply is communicatively connected to the processor.

8. A method of using the thermal depolarization compensation system according to claim 6 or 7, characterized in that It includes the following steps: Dividing the incident beam into a sampling beam and a main beam, measuring the phase space distributions of the P-polarized beam and the S-polarized beam in the sampling beam, and obtaining the phase difference space distribution of the P-polarized beam and the S-polarized beam; According to the phase difference space distribution of the P-polarized beam and the S-polarized beam, the pulse power supply outputs different pulse voltage values and loads them onto the beam polarization controllable device. The main beam is incident into the beam polarization controllable device, and the electro-optic crystal corrects the phase difference between the ordinary light and the extraordinary light of the main beam. The polarization state of the output beam reflected by the beam polarization controllable device becomes linearly polarized light, realizing thermal depolarization compensation.

9. The method of using a thermal depolarization compensation system according to claim 8, characterized in that, The incident beam is divided into a sampling beam and a main beam after passing through the sampling mirror. The sampling beam is divided into a P-polarized beam and an S-polarized beam after passing through the polarizer. The phase space distributions of the P-polarized beam and the S-polarized beam are respectively measured by the wavefront sensor, and the measured phase space distribution data is input into the processor to calculate the phase difference space distribution of the P-polarized beam and the S-polarized beam.

10. The method of using a thermal depolarization compensation system according to claim 8, characterized in that, According to the phase difference space distribution of the P-polarized beam and the S-polarized beam, the processor calculates the pulse voltage values required to be loaded on different sub-regions of the gold film grating. The pulse power supply outputs different pulse voltage values and loads them onto the gold film grating. The main beam is incident into the electro-optic crystal through the light window and the discharge chamber, and the electro-optic crystal corrects the phase difference between the ordinary light and the extraordinary light of the main beam. The polarization state of the output beam reflected by the high-reflection mirror becomes linearly polarized light.

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