JPH06250108A - Compensation optical device and astronomical telescope, optical data link, and laser working machine using same - Google Patents

Abstract

PURPOSE:To compensate the wave front distortion even for a weak light. CONSTITUTION:When an incident light 1 is reflected by a shape variable mirror 2 to compensate the distortion of a wave front 14, the reflected light is phase modulated by vibrating every region of the reflection surface of the mirror 2 using different frequencies. The phase modulated light is taken out by a beam splitter 3 and converged on a pin hole 7 by a lens 6. The converged light is interfered with a laser beam 11 outputted from a laser oscillator 9 and the light intensity is detected by a photodetector 8. A wave front controller 12 separates each phase modulated signal based on the light intensity, the amount of advance or retard of an actuator placed at each region of the mirror is decided by the signal and the regions are driven through a driving power supply 13. Since the detected each phase modulated signal is an alternating signal, the signal is amplified by the interference with the laser beam and the compensation is made for the distortion of weak light wave front whose intensity is less than the receiving level of the photodetector.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an adaptive optics device for detecting a wavefront distortion of a light wave such as a laser beam and correcting the wavefront to make the wavefront uniform, and more particularly, to accurately detect the wavefront distortion of a weak light wave. An adaptive optics device suitable for correction by
The present invention relates to an astronomical telescope, an optical data link, and a laser processing machine equipped with this adaptive optics.

[0002]

2. Description of the Related Art When observing an astronomical object with a telescope, the faint light that reaches the earth from a star passes through the atmosphere and is captured by the telescope. However, since the density of the atmosphere is uneven, the wavefront of light is Because of this, it shakes. For this reason, the image is blurred and high-precision observation cannot be performed. Therefore, for example, U.S. Pat. Nos. 3,731,103 and 39,234.
The adaptive optics apparatus described in No. 00, No. 4141652, etc. will be used. In this adaptive optics device, by using a deformable mirror whose shape of the reflecting surface can be changed to an arbitrary shape, the reflecting surface shape is distorted according to the fluctuation of the wavefront, and the incident light whose wavefront fluctuates is reflected by this reflecting surface. , I try to align the wavefronts. The control to deform the reflecting surface of the deformable mirror is to extract a part of the reflected light from the reflecting surface, collect it, detect the light intensity with a photodetector, and obtain the fluctuation of the wavefront from this light intensity. Done in.

[0003]

If the adaptive optics device according to the above-mentioned prior art is used, the wavefront can be corrected with high accuracy. Therefore, if this is applied to an astronomical telescope, its resolution is improved and optical communication is achieved. If it is used, communication efficiency is improved, and if it is used in a laser processing machine, highly accurate processing becomes possible. However, when the light is weaker than the detection sensitivity of the photodetector, the fluctuation of the wavefront cannot be detected. The purpose of adaptive optics for astronomical observation is to observe astronomical objects that can only receive very weak light. For this purpose, a photodetector with high sensitivity is used, but there is a limit.

An object of the present invention is to provide an adaptive optics device capable of detecting and correcting fluctuations in the wavefront of a light wave below the detection sensitivity of a photodetector, and an astronomical telescope using the same. .

[0005]

In the adaptive optics apparatus for detecting the wavefront distortion of a light wave (including a laser beam) and correcting the wavefront distortion, a variable shape mirror for correcting the wavefront distortion and a variable shape mirror are provided. Means for phase-modulating the light wave at different frequencies for each specific region of the reflecting surface of the mirror, and means for detecting the intensity of the laser beam after the interference of the condensed phase-modulated light wave with the laser beam. And means for controlling the deformable mirror by detecting the distortion of the wavefront from the intensity.

[0006]

[Operation] The reflecting surface of the deformable mirror is oscillated at different frequencies for each of the divided small regions, and the light wave is phase-modulated for each small region.
When this is collected and detected, the amplitudes of the plurality of frequency components included in the light intensity are proportional to the phase of the light wave in each region.
Therefore, it is possible to amplify the amplitudes of the plurality of frequency components above the light receiving level of the detector by causing a light detector, which collects the phase-modulated light waves, and a laser having the same wavelength to interfere with each other on the photodetector. it can. Therefore, it is possible to detect the fluctuation of the wavefront even with weak light.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. 1 is a block diagram of an adaptive optics apparatus according to a first embodiment of the present invention. In FIG. 1, reference numeral 1 is incident light, 2 is a variable shape mirror, 3 is a beam splitter, and 4 is reflected light reflected by the variable shape mirror 2. It becomes the light emitted from the device. 5 is an ND filter that transmits only a specific wavelength, 6 is a lens,
7 is a pinhole, 8 is a photodetector, 9 is a laser oscillator, 1
Reference numeral 0 is a lens, 11 is a laser beam, 12 is a wavefront control device, and 13 is a drive power source for the variable shape mirror 2.

In the adaptive optics device, each part of the reflecting surface of the deformable mirror 2 is moved back and forth to be distorted into a desired shape, and the incident light 1 whose wavefront is distorted due to a difference in the density of the atmosphere is reflected by this reflecting surface to generate a wavefront. It is intended to be emitted as the emitted light 4 having a uniform line. By aligning the wavefronts in this way, the resolution is improved when this is applied to an astronomical telescope, and when applied to a high-power laser processing device (the output laser beam itself is often distorted at high power). The focusing degree of the laser light is increased to improve the processing accuracy, and if it is used for optical communication, accurate communication can be performed and communication efficiency is improved.

On the back of the reflecting surface of the deformable mirror 2, for example, 3
By arranging about 0 actuators in parallel and controlling the amount of advance / retreat of each actuator, the shape of the reflecting surface is deformed. At this time, each actuator has a small distance at a different frequency (on the order of 1 kHz). The light is reflected by the reflecting surface area of each actuator so as to be phase-modulated. Then, a part of the reflected light (emitted light) 4 is taken out by the beam splitter 3 and sent to the ND filter 5. The ND filter 5 transmits only light in a specific wavelength range, and is a laser that interferes with the incident light 1.
Only light having the same wavelength as the laser wavelength of the oscillator 9 is transmitted. The transmitted light is condensed at the focal position by the lens 6, and the light passing through the pinhole 7 is detected by the photodetector 8. The light emission intensity Um in each region of the reflecting surface corresponding to each actuator is represented by the following mathematical formula 1,

[0010]

[Equation 1]

The light intensity Ip detected by the photodetector 8 when the laser beam 11 is not added is given by the following formula 2.

[0012]

[Equation 2]

The fourth term of the equation 2 represents the phase modulation signal, and its amplitude value is given by the following equation 3.

[0014]

[Equation 3]

According to the equation (3), the amplitude value is proportional to the phase of the light in the corresponding area, so that the wavefront can be detected.

Therefore, the reflected light of the deformable mirror 2 extracted by the beam splitter has a radiation intensity of the following formula 4.
When you interfere with the beam 11

[0017]

[Equation 4]

The amplitude value of each phase modulation signal is given by the following expression 5.

[0019]

[Equation 5]

The second term of this equation 5 is the portion amplified by interference. When the intensity of the incident light 1 is weak and the intensity of the reflected light 4 is weak and the intensity represented by the formula 3 becomes lower than the light receiving level of the photodetector 8, the laser beam 11 is caused to interfere. , Can be amplified above the light receiving level of the photodetector 8 and can be detected.

In FIG. 1, the laser beam 11 output from the laser oscillator 9 is converted into a lens 6 by a lens 10.
An image is formed at the focal point position created by the optical interference and the intensity is detected by the photodetector 8. The intensity Ip is input to the wavefront control device 12 to determine a command value for controlling the amount of advance / retreat of each actuator of the variable shape mirror 2, and the drive power source 13 drives each actuator of the variable shape mirror 2 to correct the wavefront. And arrange.

FIG. 2 is a block diagram of the wavefront controller 12.
The same number of control units 15 as the number of regions into which the reflecting surface of the deformable mirror 2 is divided is provided. In each control unit 15, the synchronous detector 16 detects the amplitude value represented by Formula 5, and the controller 18 determines the phase command value. Further, the output from the oscillator 17 is added to the above-mentioned phase command value, which is output to the drive power source 13 to drive the corresponding actuator, and the variable shape mirror 2 can realize phase modulation and wavefront correction. Needless to say, the oscillation frequency of the oscillator 17 in each control unit 15 is set to a different frequency.

In FIG. 1, the ND filter 5 is inserted between the beam splitter 3 and the lens 6, but if it is not interfered with the laser beam 11, the ND filter 5 will be provided at a stage subsequent to the beam splitter 3. If there is any, it can be inserted at any position. Further, the pinhole 7 improves the SN ratio of the signal by extracting the light within the diffraction limit of the lens 6, and the signal can be detected even if the pinhole 7 is omitted. At this time, it goes without saying that the light receiving surface of the photodetector 8 is set at the focal position of the lens 6. In addition, the lens 10
The image of the beam 11 is formed on the pinhole 7 by a laser.
This is for aligning the phases of the beam 11 and the lens 10 is not necessary if the wave fronts of the laser beams output from the laser oscillator 9 are aligned.

FIG. 3 is a block diagram of an adaptive optics apparatus according to the second embodiment of the present invention. As shown in FIG. 3, at the beam splitter 3, the laser beam 11 output from the laser oscillator 9 is reflected by the variable shape mirror 2 and the reflected light 4 (beam splitter 3) is phase-modulated. (Reflected light divided by)
It can also be interfered by overlapping with. After the incident light 1 is reflected by the reflecting surface of the variable shape mirror 2 while being phase-modulated, the phase-modulated signal can be amplified by overlapping the laser beam 11 from any position. It goes without saying that the wavefront can be corrected by controlling the deformable mirror 2 as described above using the light intensity Ip detected by the photodetector 8.

FIG. 4 is a block diagram of an adaptive optics apparatus according to the third embodiment of the present invention. In this embodiment, a liquid crystal matrix 19 is used instead of the deformable mirror. The liquid crystal matrix 19 is one in which liquid crystal elements are arranged two-dimensionally, and different electric fields can be applied to the respective elements. The phase of the light passing through the liquid crystal matrix 19 can be controlled by changing the applied voltage, which enables the phase modulation and the wavefront correction. In FIG. 4, the incident light 1 is phase-modulated by the liquid crystal matrix 19 and the wavefront is corrected, and the incident light 1 split by the beam splitter 3 is caused to interfere with the beam from the laser oscillator 9 to generate light. It is detected by the detector 8. The deformable mirror 2 is attached to the liquid crystal matrix 19
The configuration is the same as that of FIG. 1 except that the above is replaced, and the wavefront can be corrected by the same operation. Further, as described in the embodiment shown in FIG. 3, it goes without saying that the insertion position of the laser oscillator 9 can be changed.

FIG. 5 is a block diagram of an adaptive optics apparatus according to the fourth embodiment of the present invention. In this embodiment, both the deformable mirror 2 and the liquid crystal matrix 19 are used. The incident light 1 has its wavefront corrected by the variable shape mirror 2 and then split by the beam splitter 3, one of which is transmitted through the ND filter 5 and is phase-modulated by the liquid crystal matrix 19 at a different frequency for each liquid crystal element. The phase-modulated light is condensed by the lens 6, the laser beam 11 interferes with this, and the photodetector 8 detects the intensity Ip. The wavefront is detected using the intensity Ip and the wavefront is controlled by the deformable mirror 2 as in the above-described embodiment.

FIG. 6 is a configuration diagram when the above-described adaptive optics device is applied to an astronomical telescope. In the astronomical telescope 22 for observing the celestial body 21, the light to be observed is collimated by the lens 6 to be incident light 1 to the adaptive optics device 20. In the adaptive optics device 20, the wavefront is corrected by the method described above,
The wavefronts of incident light 1 disturbed by atmospheric fluctuations are aligned. This improves the resolution. In addition, according to the present embodiment, it is possible to correct light from a dark celestial body that could not be corrected conventionally. In the observation device 23, an astronomical image can be observed by using an integral type image pickup tube.

FIG. 7 is a block diagram of another embodiment of the astronomical telescope. As a countermeasure when the light from the celestial body 21 to be observed is weak and the wavefront cannot be detected, the laser beam 9 is used in the same direction as the celestial body 21 to be observed.
Is emitted, and the laser beam scattered by the atmosphere is measured to detect the turbulence of the wavefront. Although scattered light returns to the astronomical telescope 22 from all the propagation paths of the laser beam, it can be regarded as a point light source similar to the celestial body by narrowing the field of view of the astronomical telescope 22. This is called Laser Guide Star 25. To reduce the difference between the wavefront of the light from the celestial body 21 and the wavefront of the light from the laser guide star 25, it is necessary to raise the altitude of the laser guide star 25.
Since the laser beam is attenuated by the atmosphere, a large output laser oscillator 9 is required. Therefore, the adaptive optics device 2 of the present invention
Since the signal for wavefront detection can be amplified by using 0,
The output of the laser oscillator 9 can be suppressed.

Next, with reference to FIG. 8, an embodiment in which an adaptive optical device is applied to a laser data link for transmitting and receiving data between two distant points by a laser beam will be described. In FIG. 8, the upper part and the lower part have the same device configuration, and data is transmitted and received via the laser beam. First, the case of transmitting from the upper part to the lower part will be described. The data transmitting device 28a converts the data to be transmitted into a laser modulated signal, and the laser oscillator 9a outputs the laser. The laser beam is a deformable mirror 2a and a mirror-3.
And is transmitted to the distant receiving optical system via the transmitting optical system 27a. A laser beam is similarly transmitted from the lower transmission optical system 27b, and the upper reception optical system 26a.
Then, the laser beam is received and the beam splitter 3a is received.
As a result, one of them is converted into an electric signal by the photodetector 8a and is received as information by the data receiving device. The other is a deformable mirror 2b
Is input to the adaptive optics device 20a via the
In b, the wavefront distortion of the laser beam is corrected. Adaptive optics 2
The same control signal as the command given from 0a to the variable shape mirror 2b is also output to the variable shape mirror 2a to correct and transmit the wave front of the laser beam output from the laser oscillator 9a. If both transceivers are far apart,
Both laser beams may be considered to follow the same propagation path, and thus the wave front of the transmitted laser beam may be corrected in the manner described above. By correcting the wavefront of the laser beam in this way, the energy density at the receiving position can be increased. Although the case of transmitting from the upper part to the lower part has been described, it goes without saying that the wavefront of the laser beam can be corrected by the same operation in the opposite case.

Next, with reference to FIG. 9, an embodiment in which an adaptive optics device is applied to a laser processing machine for cutting or welding a material with a laser beam will be described. In FIG. 9, the laser beam output from the laser oscillator 9 is irradiated onto the processed material 30 via the variable shape mirror 2 and the lens 6a. The light reflected by the surface of the processed material 30 is received by the lens 6b and detected by the photodetector 8. A part of the laser beam output from the laser oscillator 9 is used as a beam splitter 3a and a lens 6.
b and the beam splitter 3b are used to interfere with the reflected light from the processed material 30. With this, by controlling the deformable mirror 2, the wavefronts of the laser irradiated on the processing material 30 are aligned, and high-precision processing becomes possible. By adopting this embodiment, even if the reflected wave from the processed material 30 is weak,
The wavefront can be detected and corrected. In the case of a laser processing machine, the laser output is high, so in addition to fluctuations in the atmosphere,
Since the wavefront is distorted by the thermal deformation of the optical system due to the z, the adaptive optics can always be applied to the workpiece 30 with a high energy density.

[0031]

According to the present invention, since the light whose wavefront is to be corrected is amplified by using the interference with the laser beam and the wavefront is detected, the wavefront of weak light below the detection limit of the photodetector is detected. Can be corrected.

Therefore, when applied to an astronomical telescope, it is possible to correct the wavefront of light from a dark celestial body, which has the effect of widening the region that can be observed with high resolution. Further, since the wavefront of weak light can be detected, the output of the laser oscillator for generating the laser guide star, which is made to detect the droop of the wavefront, can be reduced.

When it is applied to communication, it is possible to suppress the spread of the beam due to the disturbance of the wavefront generated during the propagation of the laser beam, a high arrival energy density can be obtained, and the transmission laser output can be obtained. Can be made smaller.

When it is applied to a laser processing machine, it is possible to suppress the spread of the beam due to the distortion of the optical system due to the high laser energy in addition to the disturbance of the wavefront generated during the propagation, and to irradiate the processed material. Since the laser spot can be made smaller,
Accurate processing is possible.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an adaptive optics apparatus according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram of the wavefront control device shown in FIG.

FIG. 3 is a configuration diagram of an adaptive optics device according to a second embodiment of the present invention.

FIG. 4 is a configuration diagram of an adaptive optics device according to a third embodiment of the present invention.

FIG. 5 is a configuration diagram of an adaptive optics device according to a fourth example of the present invention.

FIG. 6 is a configuration diagram of an astronomical telescope according to an embodiment of the present invention.

FIG. 7 is a configuration diagram of an astronomical telescope according to another embodiment of the present invention.

FIG. 8 is a configuration diagram of a laser data link according to an embodiment of the present invention.

FIG. 9 is a configuration diagram of a laser processing machine according to an embodiment of the present invention.

[Explanation of symbols]

1 ... Incident light, 2 ... Deformable mirror, 3 ... Beam splitter,
4 ... Emitted light, 5 ... ND filter, 6 ... Lens, 7 ... Pinhole, 8 ... Photodetector, 9 ... Laser oscillator, 10 ... Lens, 11 ... Laser beam, 12 ... Wavefront control device , 13 ...
Drive power supply, 14 ... Wavefront, 15 ... Control part, 16 ... Synchronous detector, 17 ... Oscillator, 18 ... Controller, 19 ... Liquid crystal matrix, 20 ... Compensation optical device, 21 ... Astronomical object, 22 ... Astronomical telescope, 23 ... Observation Device, 24 ... Tilt mirror, 25 ... Laser guide star, 26 ... Receiving optical system, 27 ... Transmitting optical system,
28 ... Transmitting device, 29 ... Receiving device, 30 ... Processing material.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location G02F 1/13 505 9017-2K

Claims (10)

[Claims] 1. An adaptive optics device for detecting wavefront distortion of a light wave and correcting the wavefront distortion, wherein a variable shape mirror for correcting the wavefront distortion and a light wave having a different frequency for each specific region of a reflecting surface of the variable shape mirror. A phase-modulating means, a means for detecting the intensity of the laser beam after the interference of the phase-modulated light wave and the laser beam, and a deformable mirror for detecting the wavefront distortion from the intensity. And a means for controlling the adaptive optics device. 2. An adaptive optics device for detecting a wavefront distortion of a light wave and correcting the wavefront distortion, and a variable shape mirror for correcting the wavefront distortion, and a liquid crystal in which the reflected light of the variable shape mirror with the corrected wavefront is incident light. A liquid crystal matrix in which elements are arranged two-dimensionally,
A means for phase-modulating the incident light by controlling the electric field applied to each liquid crystal element, and a laser beam that interferes with the condensed phase-modulated light wave are detected. An adaptive optics apparatus comprising: means and means for detecting distortion of the wavefront from the intensity and controlling a deformable mirror. 3. An adaptive optics device for detecting wavefront distortion of a light wave and correcting the wavefront distortion, wherein a liquid crystal matrix in which liquid crystal elements having a light wave for correcting the wavefront distortion as incident light are arranged two-dimensionally, and each liquid crystal element Control means for correcting the distortion of the wavefront of the incident light by controlling the electric field applied to the incident light and for performing phase modulation, and after the interference of the laser beam with the condensed phase-modulated light wave An adaptive optics device comprising: a unit for detecting intensity; and a unit for detecting distortion of the wavefront from the intensity and controlling the control unit. 4. The method according to claim 1, wherein the phase-modulated light wave is condensed after passing through an optical filter that transmits only a specific wavelength, and interferes with a laser beam having the same wavelength as the specific wavelength. An adaptive optics device. 5. An adaptive optics apparatus according to claim 1, further comprising means for condensing an interfering laser beam at a position where it interferes. 6. An astronomical telescope for observing an astronomical object, wherein the adaptive optics device according to claim 1 is provided, and observation is performed after correcting the wavefront distortion of the observed light. telescope. 7. The astronomical telescope according to claim 6, further comprising a laser oscillator and means for emitting a laser beam from the laser oscillator toward an astronomical object to be observed. 8. In an optical data link for transmitting information by a laser beam between two points distant from each other, means for detecting wavefront distortion from the received laser beam, and means for detecting the wavefront distortion. And a means for transmitting a laser beam having a wavefront that is phase conjugate with the above-mentioned wavefront. 9. An adaptive optical device according to any one of claims 1 to 5 is provided in an optical data link for transmitting information by a laser beam between two points distant from each other. Characteristic optical data link. 10. A laser processing machine for processing a processed material by irradiating the processed material with a laser, wherein the adaptive optics device according to claim 1 is provided, and the processed material is processed. A laser processing machine, which is characterized in that the wavefronts of laser beams to be irradiated are aligned.