JPH0484477A - Multidither system compensation optical apparatus - Google Patents

Abstract

PURPOSE:To suppress control errors due to distribution by providing a means for measuring the distribution of laser beam intensities during transmission and a means for calculating feedback gain on the basis of intensities obtained by this measuring means. CONSTITUTION:A transmission laser beam 10 outputted from a laser generator 1 is guided via a beam splitter 13 to a shape various mirror 2 and a laser beam intensity measuring instrument 7. The transmission laser beam 10 which is made to enter the shape various mirror 2 is phase modulated and collected by a light collecting system 3 onto an object 4. Reflection waves 11 from the object 4 are received by a light detector 5. The received signals are converted into electrical signals, and input to a wave-front controller 6. The phase modulation of the transmission laser beam by the variable shape mirror 2 is performed by frequencies different for each of the regions which is divided into N portions. The wave-front controller 6 comprises control sections 12 for N channels corresponding to the divide-by-N regions. The control sections have the same construction, each of which comprising a synchronization detector 6A, an oscillator 6B and a controller 6C.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is a device for propagating a laser beam in a medium such as the atmosphere to irradiate an object, in which the spread of the laser beam due to the distribution of the refractive index of the medium is suppressed. The present invention relates to an adaptive optics device.

[Conventional technology]

Conventionally, multi-dither adaptive optics devices have been described by Optical Society of America, 67.3.
March (1977) pp. 315-318 (0,
S, A, VoQ67, No3°March, 1977.
pp. 315-318).

[Problem to be solved by the invention]

The above-mentioned conventional technology has a problem in that control errors become large when the intensity distribution of the laser beam during transmission is non-uniform.

The aim of the invention is to provide a device which provides a solution to this problem.

[Means to solve the problem]

In order to achieve the above object, the present invention is provided with means for measuring the distribution of laser beam intensity during transmission and means for calculating a feedback gain from the intensity obtained by this means.

[Effect]

In the prior art, the feedback gain is constant, so if the laser beam intensity has a distribution, the intensity distribution and the phase distribution of the minute region of each laser beam cannot be distinguished, resulting in a control error.

Therefore, by first determining the intensity distribution of the laser beam during transmission and correcting the feedback gain using this distribution, control errors due to the distribution can be suppressed.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. A transmitted laser beam 1 outputted from a laser generator 1 is guided via a beam splinter 13 to a deformable mirror 2 on one side and a laser beam intensity measuring device 7 on the other side. The transmitted laser beam 10 incident on the deformable mirror 2 is phase modulated here, and focused onto the target object 4 by the focusing optical system 3. A reflected wave 11 from a target object 4 is received by a photodetector 5, the received signal is converted into an electrical signal, and the electrical signal is input to a wavefront control device 6. Phase modulation in the deformable mirror 2 is performed at a different frequency for each of the N divided regions of the transmitted laser beam. The wavefront control device 6 includes N-channel control sections 12 corresponding to the number of N divided regions. Each control section (12A to 12
N, N channels) have exactly the same configuration, and a synchronous detector 6A.

It consists of an oscillator 6B and a controller 6C. However, the oscillation angular frequency (ω1゜ω2...) of the oscillator 6B of each control unit 12
...ωN) differs for each channel. Photodetector 5
First, the synchronous detector 6A detects only the frequency components that are the same as the oscillation angular frequency of each channel, and outputs the received signals to the controller 6C. The controller 6C amplifies the input signal (gain G) L
, is defined as the control phase φ1c. Similarly, control phases φ2C+φsct...φNC are generated by each control unit 12, the output signal (ψsinω, 1) of the oscillator 6A and the control phase φ1° are added, and N phases ( ΦI
C, Φ2C,...ΦNc; ΦIC=Φ1c10'p
sin ω work 1) A command signal is output. A signal proportional to the phase command signal is input to the deformable mirror 2 to perform phase modulation and phase control of the laser. On the other hand, the transmitted laser beam 10 inputted to the laser beam intensity measuring device 7 by the beam splitter 13 is divided into N parts, and the laser intensity is measured for each region.The result is inputted to the gain determination circuit 8, and the laser intensity is measured for each region by the controller 6C. Gain G (G 11
G z,...GN) is determined.

The above are the functions of each part of FIG. 1, which is an embodiment of the present invention.The method for determining the gain G, which is the key point of the present invention, will be described in detail below. First, the laser radiation intensity Uyo of the N-divided region of the transmitted laser beam 10 output from the deformable mirror 2 is expressed by the following equation.

U m = A m U o e jΦ”
, iF) Φll2 −φmc + 'f' s
in (1) II Phase when transmitting (mth) A,: Beam intensity coefficient φ, c: Control phase (mth) ψ: Modulation amplitude ω,: Variable frequency angular frequency) Transmitting laser The m-th laser radiation intensity when the beam 10 is focused by the focusing optical system 3 and reaches the target 4 is the same as the above equation.

U * = A m U o e jΦ′
...(2) However, Φ, knee φmc + Y'sinωm
t+φI+dφ, 4: Phase disturbed by propagation into the atmosphere (
(hereinafter referred to as the disturbance phase). Assuming that the area of the target 4 that reflects the transmitted laser beam 10 is smaller than the focusing limit determined by the focusing optical system 4 and the laser wavelength, the received signal Ip detected by the photodetector 5 will be k? ! :Q However, Uo: Radiation intensity at the time of transmission kl-Q...(3) However, when φ1=φ, -φkC...(4) φkack-th disturbance phase φhc* and th control phase Jo:' ○th order Bessel function Js with f' as an argument: CP
The output of the synchronous detector 6A of each control unit 12 takes out only the amplitude of the modulation angular frequency component ω1, so if the output is S, then Ω ≠ Fertilization (5) Here, by setting ψ1−φ□ φ and linearizing equation (5), the transmitted laser beam 10 becomes uniform (Am=11m=1°2・
...N), and if the controller 6C performs the following calculation, φ1m C” G II・S,
...(7) From formulas (4), (6), and (7), K, = K(N-1)・G.

is obtained. From equation (8), if K is large, φ. Eveningφ,,
−(9), therefore, φ1=φ, d−
From φ1=φ2=・・・・・・=φ,=・・・・・・
=φN=O·(10), and the phases φ of the N-divided laser beams can be matched.

A case where the transmitted laser beam 10 is non-uniform will be described.

At this time, in the case of a uniform beam, the control phase φ1c is expressed as (7)
If it is determined in the same way as the formula, the following problem arises. In other words, equations (5), (6), and (7) are correct...(6) Therefore, from A, ≠ 1 (m=1.2.-N), (1
1) The variation in the second term of the equation affects the control of φ1c.

As a solution to this problem, it is sufficient to detect A and change the gain G. That is, each gain G1 is G, = G/A,
...If determined by (12), each control phase φ work. ,...φNc is Q≠m However, 1=Kz=...KN=K(N-1)・G ・
(15), and the deviation between the control phase φ and the disturbance phase φ, 6 is constant even if each control channel m is different, so the overall deviation is also small. In other words, since the present invention solves the variation in deviation for each control channel caused by non-uniformity of the transmitted laser beam by correcting the gain G, the deviation can be further reduced.

Note that if the intensity distribution of the transmitted laser beam 10 does not vary over time, it is sufficient to measure the -degree intensity distribution and perform gain correction, and then control the adaptive optics device to keep the gain fixed during operation. can be easily inferred.

〔Effect of the invention〕

According to the present invention, even when the intensity distribution of a transmitted laser beam is non-uniform, phase control with small deviation can be performed.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of one embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Laser generator, 2... Deformable mirror, 3 Condensing optical system, 4... Target, 5... Photodetector, 6... Wavefront control device, 6A... Synchronous detection device, 6B... oscillator,
6c. Controller, 7. Laser beam intensity measuring device, 8. Gain determining circuit, 9. Drive power supply.

Claims (1)

[Claims] 1. A laser generator that suppresses the spread of the laser beam that occurs when the laser beam is propagated in a medium, and a phase distribution of the laser beam that is different for each region in which the laser beam is divided into N. A variable shape mirror capable of phase modulation with frequency, a photodetector for detecting the laser beam propagated in a medium, means for separating and detecting only the N phase modulation frequency components from the output signal of the photodetector, and the separate detection. A multi-dither adaptive optics device is provided with a means for determining the shape of a deformable mirror based on a signal obtained by measuring the intensity of the laser beam outputted from a laser generator, and a means for measuring the intensity of the laser beam output from the laser generator, 1. A multi-dither type adaptive optics device, comprising means for determining the shape of the deformable mirror based on the intensity of the N divided regions and the N phase modulation frequency components.