CN110045496A - A kind of Sodium guide star atmospheric laser link compensation system - Google Patents

Abstract

The present invention relates to adaptive optics system technical fields, more particularly to a kind of Sodium guide star atmospheric laser link compensation system comprising first laser beam-expanding system, dichronic mirror, distorting lens, closes beam beam-expanding system, Wavefront detecting and control system, reflecting mirror and Calibrating source at second laser beam-expanding system.The system laser different from sodium optical maser wavelength with another beam, the transmitting of combiner Shared aperture is swashed with sodium, it is assembled at the atmosphere on sodium laser emission path, generate atmospheric backscatter, it is measured using back scattering image and compensates atmospheric turbulance distortion, the phase distortion opposite with atmospheric turbulance can be then carried when sodium laser emitting, it is offseted by atmospheric turbulance Shi Yuqi, when sodium laser being made to reach the convergence of sodium layer, it is distributed with flatter wavefront, spot diameter is smaller, energy density is higher, be conducive to reduce ground-based optical telescope adaptive optics system measurement error, improve image correction effect.

Description

A laser atmospheric link compensation system for sodium guide stars

technical field

The invention relates to the technical field of adaptive optical systems, in particular to a sodium guide star laser atmospheric link compensation system.

Background technique

The sodium guide star laser technology refers to the use of a laser whose center frequency can resonate with the transition spectrum of sodium atoms to excite the sodium layer at a height of about 92km from the ground to emit resonant backscattered light. High altitude advantage. However, in practical applications, the upward transmission process of the sodium guide star laser beam will be disturbed by atmospheric turbulence, the laser wavefront distribution will be distorted, the convergence characteristics in the sodium layer will deteriorate, the star point will spread, and the center intensity will decrease, that is, the sodium guide star’s intensity As the angular width increases, the brightness decreases, which in turn leads to an increase in the measurement wavefront error of the adaptive optics system of the main telescope, which reduces the effect of correction and high-resolution imaging.

In view of this, it has become an urgent technical problem to be solved in the art to overcome the above defects in the prior art and provide a new sodium guide star laser atmospheric link compensation system.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a sodium guide star laser atmospheric link compensation system for the above-mentioned defects of the prior art.

The purpose of the present invention can be achieved through the following technical measures:

The invention provides a sodium guide star laser atmospheric link compensation system, which includes:

A first laser beam expanding system, a dichroic mirror, a deformable mirror and a beam combining beam expanding system are arranged in sequence along the emission optical path, a wavefront detection and control system located in the reflection direction of the dichroic mirror, a A second laser beam expander system in the incident direction of the beam system, a reflector and a calibration light source disposed between the deformable mirror and the beam combining beam expander system, the reflector is used to cut in/cut the calibration light source light path;

The first laser beam expanding system is used for emitting a first laser and collimating and expanding the first laser; the second laser beam expanding system is used for emitting a second laser and collimating the second laser Direct beam expansion; the wavefront detection and control system includes a wavefront detector and a wavefront controller, the wavefront detector is used to measure the wavefront phase distribution information, and the wavefront controller is used to process the wavefront phase distributing information and outputting control signals required by the deformable mirror;

The first laser emitted by the first laser beam expanding system is sequentially emitted to free space through the dichroic mirror, the deformable mirror, and the beam combining beam expanding system and converges at the sodium layer, and the second laser beam expands. The second laser emitted by the beam system passes through the beam combining and expanding system and is emitted to free space and converges at the atmosphere to generate a return beam, and the return beam passes through the beam combining and expanding system, the deformable mirror, and the color separation in sequence. After the mirror enters the wavefront detection and control system, before the wavefront detector and the wavefront controller work, the wavefront controller controls the mirror to cut the calibration light source into the optical path to calibrate The control matrix of the wavefront controller, after the calibration is completed, the wavefront controller controls the mirror to cut the calibration light source out of the optical path, and the wavefront detector measures the wavefront phase distribution information of the returned beam, The wavefront controller processes the wavefront phase distribution information and outputs the control signal required by the deformable mirror to control the deformable mirror to generate a surface shape opposite to the current wavefront, so as to cancel the wavefront of the returning beam, so as to achieve The wavefront pre-compensation is performed after the first laser emitted by the first laser passes through the deforming mirror.

Preferably, the first laser beam expanding system includes a first laser and a first beam expander arranged in sequence, and the first laser beam is collimated and expanded by the first beam expander and then enters the dichroic mirror.

Preferably, the second laser beam expanding system includes a second laser and a second beam expander arranged in sequence, and the second laser is collimated and expanded by the second beam expander and then enters the beam combining beam expanding system .

Preferably, the linear polarization direction of the first laser light and the linear polarization direction of the second laser light are perpendicular to each other.

Preferably, the beam combining and expanding system includes: a polarizing beam splitter, a quarter-wave plate and a third beam expander arranged in sequence, and the first laser light exits from the deformable mirror and passes through the polarizing beam splitter in sequence After the mirror, the quarter-wave plate and the third beam expander, it is emitted into free space and converged at the sodium layer, and the second laser is emitted from the second laser beam expander and passes through all the After the polarizing beam splitter, the quarter wave plate and the third beam expander are emitted into free space and converged at the atmosphere.

Preferably, the wavefront detection and control system further comprises: a beam reducer, an optical switch, a high-voltage amplifier, a retarder and a high-voltage driver, the beam reducer narrows the return beam from the dichroic mirror to a transmission location. The optical switch has an aperture consistent with the input of the wavefront detector, and the retarder and the high voltage driver control the optical switch to selectively pass the return beam, and the wavefront detector measures the light passing through the optical switch. The wavefront phase distribution information of the returned beam, the wavefront controller collects the wavefront phase distribution information and calculates the control voltage, and the high-voltage amplifier amplifies the control voltage and controls the deformable mirror to generate a wavefront opposite to the current wavefront face shape.

Preferably, the delay device is connected in communication with the second laser, and the delay device controls the operation state of the optical switch according to the synchronization signal of the second laser.

Preferably, the first laser is a sodium laser, and the wavelength of the second laser is different from that of the first laser.

The system of the present invention utilizes two laser beams to be combined and emitted with a common aperture, the second laser beam converges at the atmosphere on the first laser transmission path, and generates atmospheric backscattering, and the backscattered image is used to measure and compensate for atmospheric turbulence distortion. When the laser exits, it will carry the phase distortion opposite to that of the atmospheric turbulence, and it will offset it when passing through the atmospheric turbulence, so that when the first laser reaches the sodium layer and converges, it has a flatter wavefront distribution, a smaller spot diameter, and a higher energy density. , which is conducive to reducing the measurement error of the adaptive optics system of the ground-based optical telescope and improving the imaging correction effect.

Description of drawings

1 is a schematic structural diagram of a sodium guide star laser atmospheric link compensation system of the present invention.

Among them: 1 first laser, 2 first beam expander, 3 dichroic mirror, 4 deformable mirror, 5 polarizing beam splitter, 6 quarter wave plate, 7 third beam expander, 8 second laser, 9 first 2 beam expanders, 10 beam reducers, 11 optical switches, 12 wavefront detectors, 13 wavefront controllers, 14 high voltage amplifiers, 15 retarders, 16 high voltage drivers, 17 wavefront detection and control systems, 18 first laser Beam expander system, 19 second laser beam expander system, 20 beam combination beam expander system, 21 calibrated light source, 22 reflector.

Fig. 2 is the working sequence diagram of the optical switch when the sodium guide star laser atmospheric link compensation system of the present invention is at a zenith angle of 0°.

FIG. 3 is a working sequence diagram of the optical switch when the sodium guide star laser atmospheric link compensation system of the present invention is at a zenith angle of 60°.

FIG. 4 is a light path direction diagram of a mirror cut at -45 degrees in the sodium guide star laser atmospheric link compensation system of the present invention.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.

In order to make the description of the present disclosure more detailed and complete, the following provides an illustrative description of the embodiments and specific embodiments of the present invention; but this is not the only form of implementing or using the specific embodiments of the present invention. The features of various specific embodiments as well as method steps and sequences for constructing and operating these specific embodiments are encompassed in the detailed description. However, other embodiments may also be utilized to achieve the same or equivalent function and sequence of steps.

The embodiment of the present invention discloses a sodium guide star laser atmospheric link compensation system. The system uses another laser with a wavelength different from that of the sodium laser, combined with the sodium laser to emit with the same aperture, and the atmosphere on the transmission path of the sodium laser is emitted. Atmospheric turbulence distortion is measured and compensated for by backscattering images using techniques such as time gating, polarization spectroscopy, and spectral color separation. When the sodium laser is emitted, it will carry phase distortion opposite to that of atmospheric turbulence. , when it passes through the atmospheric turbulence, it cancels it out, so that when the sodium laser reaches the sodium layer and converges, it has a flatter wavefront distribution, a smaller spot diameter, and a higher energy density, which is conducive to reducing the measurement error of the adaptive optics system of ground-based optical telescopes , to improve the image correction effect.

Fig. 1 shows a sodium guide star laser atmospheric link compensation system, the system includes: a first laser beam expander system 18, a dichroic mirror 3, a deformable mirror 4 and a beam combining beam expanding system arranged in sequence along the emission optical path 20, the wavefront detection and control system 17 located in the reflection direction of the dichroic mirror 3, the second laser beam expansion system 19 located in the incident direction of the beam combination beam expansion system 20, and the second laser beam expansion system 19 located between the deformable mirror 4 and the beam combination beam expansion system 20. Between the reflector 22 and the calibration light source 21, the reflector 22 is used to cut the calibration light source 21 into/out of the optical path.

The first laser light emitted by the first laser beam expander system 18 passes through the dichroic mirror 3, the deformable mirror 4, and the beam combining beam expander system 20 in sequence and is emitted to the free space and the sodium layer at a distance of about 92 km from the ground (the thickness of the sodium layer is about 10 km). ) converge and excite the sodium atoms to emit resonantly scattered light.

Since the first laser will be affected by atmospheric turbulence during the transmission process, a diffusion effect will appear in the sodium layer, and the central energy density will decrease. Therefore, the first laser emitted by the first laser beam expanding system 18 needs to be exposed to the atmosphere during the transmission process. Compensation for turbulent wavefronts. The second laser emitted by the second laser beam expanding system 19 is emitted to free space through the beam combining beam expanding system 20 and converged at the atmosphere to generate backscattered beams. The height of the atmosphere from the ground may be 15km, but not limited to 15km, and the The backscattered beam in the reflected light path is the return beam, and the return beam passes through the beam combining and expanding system 20, the deformable mirror 4, and the dichroic mirror 3 in turn and then enters the wavefront detection and control system 17. The wavefront detection and control system 17 measures the return. The wavefront (that is, atmospheric turbulence) phase distribution information of the beam, and the phase distribution information of the wavefront is processed, and the control voltage required by the output deforming mirror 4 controls the deforming mirror 4 to generate a surface shape opposite to the current wavefront to offset the interference of atmospheric turbulence. , according to the principle of reversibility of the optical path, the first laser emitted by the first laser beam expansion system 18 carries the corresponding wavefront compensation after passing through the deformable mirror 4, and is corrected in time when passing through the atmospheric turbulence, and has a relatively flat wave when reaching the sodium layer. The front phase distribution can improve the energy concentration of the converging spot, thereby reducing the angular width distribution of the sodium guide star and improving its brightness.

The first laser beam expanding system 18 is used for emitting a first laser and collimating and expanding the first laser. The first laser is a sodium laser. The first laser beam expanding system 18 includes a first laser 1 and a second laser arranged in sequence. A beam expander 2, the first laser emitted by the first laser 1 is linearly polarized light, and its linear polarization direction is the vertical direction, the first laser 1 is a laser that needs pre-compensation, and the first beam expander 2 has focusing and variable It can realize that the first laser can be focused on the sodium layer at about 92km under different zenith angles.

The second laser beam expanding system 19 is used for emitting a second laser and collimating and expanding the second laser. The wavelength of the second laser is different from that of the first laser. In this embodiment, the wavelength of the first laser is 589 nm. The wavelength of the second laser can be 532nm or 355nm, but is not limited to 532nm or 355nm. The second laser beam expanding system 19 includes a second laser 8 and a second beam expander 9 arranged in sequence. The second laser emitted by the second laser 8 is linearly polarized light, and its linear polarization direction is the horizontal direction, that is, the first laser The linear polarization direction is perpendicular to the linear polarization direction of the second laser beam. The second beam expander 9 has the functions of focusing and zooming, which can realize that the second laser beam can be focused in the atmosphere at about 15km under different zenith angles. .

The dichroic mirror 3 transmits the first laser light and reflects the second laser light; the deformable mirror 4 can change the surface shape and adjust the optical path of the light beam passing through its surface.

The beam combining and expanding system 20 includes: a polarizing beam splitter 5, a quarter-wave plate 7 and a third beam expander 7 arranged in sequence, wherein the polarizing beam splitter 5 can transmit the beam of a certain polarization direction, but reflect the same as the beam. The light beam in the vertical polarization direction, in this embodiment, the polarization beam splitter 5 transmits the linearly polarized light in the vertical direction (ie the first laser light), and reflects the linearly polarized light in the horizontal direction (ie the second laser light); The wave plate 7 can work in the first laser band and the second laser band at the same time, and the light beam passing through the quarter wave plate 7 has a phase delay of 90°, and the quarter wave plate 7 can realize linearly polarized light Mutual conversion with circularly polarized light, in this embodiment, the quarter-wave plate 7 can convert the linearly polarized light emitted from the emission light path to the free space into circularly polarized light, and can also return from the free space to the circularly polarized light. The circularly polarized light of the emission light path is converted into linearly polarized light; the third beam expander 7 is used to change the diameter of the beam.

The wavefront detection and control system 17 includes: a beam reducer 10 , an optical switch 11 , a wavefront detector 12 , a wavefront controller 13 , a high voltage amplifier 14 , a retarder 15 and a high voltage driver 16 , and the return beam is first transmitted by the beam reducer 10 Compressed to an aperture that can transmit the optical switch 11 and is consistent with the input of the wavefront detector 12, the optical switch 11 is controlled by the retarder 15 and the high-voltage driver 16 to selectively pass the return beam, and only the return beam within a certain range near the detection height can be Entering the wavefront detector 12, the wavefront detector 12 measures the return beam passing through the optical switch 11, collects the wavefront phase information of the return beam, and the wavefront controller 13 collects the wavefront phase information and calculates the corresponding control voltage , and the control voltage is amplified by the high-voltage amplifier 14 to control the deformable mirror 4 to generate a surface shape opposite to the current wavefront, so as to cancel the wavefront of the returning beam.

Further, the delay device 15 is connected in communication with the second laser 8, and the delay device 15 is triggered by the synchronization signal of the second laser 8, and outputs the corresponding frequency and width pulse signals according to the zenith angle of the transmitting telescope to control the delay and opening of the optical switch 11. The closing time and thus the timing and width of the return beam entering the wavefront detector 12 are controlled.

In this embodiment, please refer to Fig. 2. Fig. 2 uses a 532nm laser with a repetition rate of 1kHz, a pulse of 10ns, and a zenith angle of 0° as an example to demonstrate the return beam with a center located at 15km and a depth of 600m. The pulse timing diagram for selective passing, at this time, the vertical distance from the center to the ground is 15km, here it is assumed that the height of the atmosphere that can generate backscattered light is 30km, and the influence of the pulse width on the timing is ignored. Assuming that it is time t ₀ when each pulse is emitted, the retarder 15 turns on the optical switch 11 after a delay of 98 μs, and closes it at 102 μs. Here, only the part of the return beam passing through the optical switch 11 between 98 μs and 102 μs is: The part of the wavefront detector 12 that needs to be measured. In another preferred embodiment, please refer to Fig. 3. Fig. 3 is an example of a 532 nm laser with a repetition frequency of 1 kHz, a pulse of 10 ns, and a zenith angle of 60°. Return the pulse timing diagram of the selective passing of the beam. At this time, the distance from the center to the telescope is 30km, the vertical distance from the center to the ground is still 15km, and the vertical sampling distance is still 600m. At this time, the opening time of the optical switch 11 is between 196 μs and 204 μs after the pulse is sent out. Here, only the part of the returning beam passing through the optical switch 11 between 196 μs and 204 μs is the part that the wavefront detector 12 needs to measure.

Further, the calibration light source 21 can emit a light source with an ideal plane wave wavefront distribution larger than the diameter of the deformable mirror 4 . Furthermore, the reflector 22 is arranged on the electric translation stage, and the wavefront controller 13 is connected to the electric translation stage for control and drives the reflector 22 to cut in/out of the optical path by controlling the movement of the electric translation stage. Before the front controller 13 works, the wavefront controller 13 controls the reflector 22 to cut into the optical path, and the reflector 22 cuts into the calibration light source 21 to calibrate the control matrix of the wavefront detector 12. After the calibration is completed, the wavefront controls The controller 13 controls the mirror 22 and the calibration light source 21 to cut out.

Specifically, in this embodiment, please refer to FIG. 1 , after the first laser light (linearly polarized light) emitted by the first laser 1 is expanded by the first beam expander 2 to the aperture matching the deformable mirror 4 , it transmits Pass through the dichroic mirror 3, and then pass through the deforming mirror 4, the polarizing beam splitter 5, the quarter wave plate 7 (here the linearly polarized light is converted into circularly polarized light) and the third beam expander 7, and then emitted to free space , the sodium layer at a distance of about 92km from the ground converges and excites the sodium atoms there to emit resonance scattering light; after the second laser (linearly polarized light) emitted by the second laser 8 is expanded by the beam expander, the polarized beam splitter 5 is reflected, and passes through the quarter-wave plate 7 (here, the linearly polarized light is converted into circularly polarized light) and the third beam expander 7, and is emitted to free space, where it converges at the atmosphere about 15km from the ground, and After interacting with atmospheric molecules, it emits backscattered light (ie, a return beam). The returned beam first passes through the third beam expander 7 to compress the diameter, and then passes through the quarter-wave plate 7 to convert the circularly polarized light into linearly polarized light, and the polarization direction is perpendicular to the original polarization direction, and then transmits through the polarization beam splitter 5 and The wavefront detection and control system 17 reaches the wavefront detection and control system 17 after being reflected by the deformable mirror 4 and the dichroic mirror 3 in sequence.

The return light is first compressed by the beam reducer 10 to an aperture that can transmit the optical switch 11 and is consistent with the input of the wavefront detector 12. The retarder 15 and the high-voltage driver 16 control the optical switch 11 to selectively pass through the return beam, and the wavefront detection The controller 12 measures the return beam passing through the optical switch 11 and collects the wavefront phase information of the return beam. The wavefront controller 13 collects the wavefront phase information and calculates the corresponding control voltage. The control voltage is amplified by the high voltage amplifier 14 and then controlled The deformable mirror 4 produces a surface shape opposite to the current wavefront to cancel the wavefront of the returning beam. Before the wavefront detector 12 and the wavefront controller 13 work, please refer to FIG. 4 , the wavefront controller 13 controls the mirror 22 to cut into the optical path at an angle of -45 degrees, and the calibration light source 21 is connected to the optical path to calibrate the wavefront control After the calibration is completed, the wavefront controller 13 controls the mirror 22 and the calibration light source 21 to cut out the optical path. According to the principle of reversibility of the optical path, the first laser emitted by the first laser beam expanding system 18 carries the corresponding wavefront compensation after passing through the deformable mirror 4, and is corrected in time when passing through the atmospheric turbulence, and has a relatively flat wavefront when it reaches the sodium layer. The phase distribution can improve the energy concentration of the converging light spot, thereby reducing the angular width distribution of the sodium guide star and improving its brightness.

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

Claims (8)

1. a sodium guide star laser atmospheric link compensation system, is characterized in that, this system comprises: A first laser beam expanding system, a dichroic mirror, a deformable mirror and a beam combining beam expanding system are arranged in sequence along the emission optical path, a wavefront detection and control system located in the reflection direction of the dichroic mirror, a A second laser beam expander system in the incident direction of the beam system, a reflector and a calibration light source disposed between the deformable mirror and the beam combining beam expander system, the reflector is used to cut in/cut the calibration light source light path; The first laser beam expanding system is used for emitting a first laser and collimating and expanding the first laser; the second laser beam expanding system is used for emitting a second laser and collimating the second laser Direct beam expansion; the wavefront detection and control system includes a wavefront detector and a wavefront controller, the wavefront detector is used to measure the wavefront phase distribution information, and the wavefront controller is used to process the wavefront phase distributing information and outputting control signals required by the deformable mirror; The first laser emitted by the first laser beam expanding system is sequentially emitted to free space through the dichroic mirror, the deformable mirror, and the beam combining beam expanding system and converges at the sodium layer, and the second laser beam expands. The second laser emitted by the beam system passes through the beam combining and expanding system and is emitted to free space and converges at the atmosphere to generate a return beam, and the return beam passes through the beam combining and expanding system, the deformable mirror, and the color separation in sequence. After the mirror enters the wavefront detection and control system, before the wavefront detector and the wavefront controller work, the wavefront controller controls the mirror to cut the calibration light source into the optical path to calibrate The control matrix of the wavefront controller, after the calibration is completed, the wavefront controller controls the mirror to cut the calibration light source out of the optical path, and the wavefront detector measures the wavefront phase distribution information of the returned beam, The wavefront controller processes the wavefront phase distribution information and outputs a control signal required by the deformable mirror, and controls the deformable mirror to generate a surface shape opposite to the current wavefront, so as to cancel the wavefront of the returning beam, thereby The wavefront pre-compensation is realized after the first laser emitted by the first laser passes through the deforming mirror. 2. The sodium guide star laser atmospheric link compensation system according to claim 1, wherein the first laser beam expanding system comprises a first laser and a first beam expander arranged in sequence, and the first laser beam After collimated and expanded by the first beam expander, the beam enters the dichroic mirror. 3. The sodium guide star laser atmospheric link compensation system according to claim 1, wherein the second laser beam expanding system comprises a second laser and a second beam expander arranged in sequence, and the second laser beam After collimating and expanding the beam through the second beam expander, it enters the beam combining beam expanding system. 4 . The sodium guide star laser atmospheric link compensation system according to claim 1 , wherein the linear polarization direction of the first laser and the linear polarization direction of the second laser are perpendicular to each other. 5 . 5. The sodium guide star laser atmospheric link compensation system according to claim 1, wherein the beam combining beam expanding system comprises: a polarizing beam splitter, a quarter wave plate and a third beam expander arranged in sequence After exiting from the deformable mirror, the first laser passes through the polarizing beam splitter, the quarter-wave plate and the third beam expander in sequence, and then is emitted into free space and converged at the sodium layer , the second laser is emitted from the second laser beam expanding system and then passes through the polarizing beam splitter, the quarter-wave plate and the third beam expander in sequence, and then is emitted into free space and in the atmosphere meet up. 6. The sodium guide star laser atmospheric link compensation system according to claim 1, wherein the wavefront detection and control system further comprises: a beam reducer, an optical switch, a high-voltage amplifier, a delay device and a high-voltage driver, The beam reducer reduces the return beam from the dichroic mirror to an aperture that transmits the optical switch and is consistent with the input of the wavefront detector, and is controlled by the retarder and the high voltage driver. The optical switch selectively passes the return beam, the wavefront detector measures the wavefront phase distribution information of the return beam passing through the optical switch, and the wavefront controller collects the wavefront phase distribution information and solves the control voltage , the high-voltage amplifier amplifies the control voltage and controls the deformable mirror to generate a surface shape opposite to the current wavefront. 7. The sodium guide star laser atmospheric link compensation system according to claim 3 or 6, wherein the delay device is connected to the second laser in communication, and the delay device is based on the synchronization signal of the second laser The operating state of the optical switch is controlled. 8 . The sodium guide star laser atmospheric link compensation system according to claim 1 , wherein the first laser is a sodium laser, and the wavelengths of the second laser and the first laser are different. 9 .