JPH02259615A - Laser transmitter - Google Patents

Abstract

PURPOSE:To efficiently converge a laser beam onto a target object surface by constituting lasers of respective wavelengths and respective elements of a variable-shape mirror in such a manner that these lasers and elements can correspond one to one. CONSTITUTION:The laser beam outputted from a laser generator 1 is inputted to a wavelength converter 2 by which the laser beam is converted to different wavelengths by each of the respective regions (the min. regions where shapes can be varied) of the variable-shape mirror 3. An optical system 4 is so designed that the laser beam reflected by the variable-shape mirror 3 (wavelength lambda1 to lambdan, n: the number of regions) is converged onto the target surface. The interference signals (beat signals) of the differences between respective frequencies are obtd. if the reflected waves 9 of the laser beam from the target 5 are detected by a photodetector 6. The signals are separated by a frequency discriminator to each component of the differences between the respective frequencies and the amplitude values thereof are detected. The shape of the variable-shape mirror 3 is so determined by a phase control circuit 8 that the detected amplitude values are to be maximized. The beam intensity on the target surface is maximized in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a laser transmitter that propagates a laser beam in a medium.

[Conventional technology]

The technique for suppressing the diffusion of the laser beam in the atmosphere and concentrating it is based on the reflector perturbation method, as described in the Journal of the Institute of Electrical Engineers of Japan 102.507 (19g2) "Adaptive Optical System".

This is because the optical aperture that sends out the laser beam is composed of N small apertures, and the overlap of the far-field pattern created by the N small apertures on the object plane causes phase distortion from each of the N small apertures to the object. We use a detection method that knows the At this time, each small aperture receives phase modulation of about 1/20 wavelength at an independent frequency f1.

[Problem to be solved by the invention]

The above conventional technology has the following problems.

One is that each aperture must be vibrated by an actuator in order to apply phase modulation to each aperture. The larger the numerical aperture N, the better the compensation efficiency, but with existing actuators (mainly piezoelectric elements), the upper limit of modulation is about 50 KHz, and this method requires assigning individual modulation frequencies to each aperture. Therefore, the numerical aperture N is limited.

The second problem is that the signal-to-noise ratio is poor due to phase modulation. In particular, when there are irregularities or vibrations (movements) on the object surface, this method may cause the laser phase to be disturbed, resulting in loss of control.

An object of the present invention is to focus a laser beam onto a target object plane.

[Means to solve the problem]

The above object is achieved by introducing laser beams with different wavelengths instead of phase modulation.

[Effect]

The principle of the present invention in which a plurality of laser beams with different wavelengths are used to converge onto an object plane will be explained.

For simplicity, the case of two different laser beams will be described. The intensity of the three laser beams is expressed by the following formula: Ia = Ce""°1゛1°) - (3) where ωt: oscillation frequency (z1/λ λ: wavelength) Ti
Two phases A, B, C: amplitude of each laser When these three laser beams are converged and the reflected wave from the target surface is detected by a photodetector, the signal P is p=l It+
Iz+Ial"=:Az+B"+C2+2ABcos((c,+t-ω
z)t+'f'1-'Pz)+2BCCO8(((11
2-ωa)t+'Pz-Y'a)+2CACO8(((
IJ3-(111)t+'P3-Y't)
(4) As is clear from the above equation, the component of the difference in the oscillation frequency of each laser beam can be detected. Therefore, since each frequency component of the signal P from the photodetector changes due to causes such as atmospheric fluctuations, the phase ψ is always controlled so that each frequency component is maximized. In order to control the phase ψ, it is sufficient to use a deformable mirror that can change the optical path length of the laser, and therefore the laser of each wavelength and each element of the deformable mirror are configured to correspond one-to-one.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. 1st
At @, the laser transmitter includes a wavelength converter 2 that changes the wavelength of the laser beam output from the laser generator 1, and a wavelength converter 2 that changes the optical path length (phase) of each laser beam output from the wavelength converter 2. Deformable mirror 3 and Deformable mirror 3
an optical system for imaging a laser beam reflected from a target object 5 at a specific focal length; a photodetector 6 for detecting the reflected wave 9 when the laser beam hits a target object 5;
from a frequency discriminator 7 that discriminates each frequency component of a signal output from the laser beam, and a phase control circuit 8 that controls the shape of the variable shape mirror 3 and outputs a command to change the optical path length (phase) of the laser beam. Become.

Next, the operation of this embodiment will be explained. First, the theoretical basis of the present invention will be explained using FIG. 3.

Output from three laser generators 1a, lb, lc 1o=
1゜e−j((!xt+'p°)・(6) However, ω1
．． ω2. ω8: Each laser oscillation frequency 'Pitψ2. ψ3
: Phase Io of each laser: Laser amplitude When the laser beam shown in the above equation is focused by an optical system, when the laser beam propagates through a medium such as the atmosphere, thermal lens effects or fluctuations in the refractive index of the medium occur. A phenomenon occurs in which the beam diverges.

At this time, each of the laser beams reaching the target surface attenuates its amplitude and changes its phase during propagation. The three beams superimpose on the target surface to a maximum when their phases are equal or when the phase difference is 2nπ (n=o, ±1.±2°, . . . ). In the prior art, the phase disturbance r' is detected and controlled. In contrast, one embodiment of the present invention provides that each laser beam If, I2.

By detecting the interfering signal or the individual oscillation frequency components, the mirror 3a of the deformable mirror 3 is moved to change the optical path length (that is, the phase) so that the detected signal is maximized. It is intended to be controlled.

An embodiment of the present invention will be described based on FIG.

A laser beam output from a laser generator 1 is input to a wavelength converter 2, and the wavelength of the laser is converted to a different wavelength for each region (the smallest region whose shape can be varied) of the deformable mirror 3. (Wavelength λ1~λ.

(n: number of regions) The optical system 4 is designed so that the laser beam reflected by the deformable mirror 3 is converged on the target surface.

The reflected wave 9 of the laser beam from the target object 5 is detected by a photodetector 6.
When detected, an interference signal (beat signal) of each frequency difference is obtained. This signal is separated into frequency difference components by a frequency discriminator, and the amplitude values thereof are detected.

The shape of the deformable mirror 3 is determined by the phase control circuit 8 so that the detected amplitude value becomes maximum. Normally, it is sufficient for the control width of the optical path length of each region of the deformable mirror 3 to be ±2λ (λ: wavelength). Therefore, this can be achieved by changing the optical path length within the range of ±2λ and searching for the optical path length (shape) that maximizes the amplitude value detected by the frequency discriminator 7.

According to this embodiment, the detection method using the wavelength (oscillation frequency) of the laser allows the state of the reflective surface of the target to be controlled, or even when the target is moving, to detect differences in frequencies. , does not fluctuate, so this control method can be applied.

In the above embodiment, a method for detecting interference between individual laser beams has been described. Next, the present invention will be explained in detail using FIG. 2. That is, the reflected wave 9 is input to the wavelength analyzer 12, and the wavelength analyzer 12 can detect the amplitude value for each wavelength of the reflected wave. Based on this detected value, the same procedure as in the first embodiment can be performed. The shape of the deformable mirror 3 can be determined by the phase control circuit 8.

Next, an embodiment in which laser beams of different wavelengths are generated for each region of the deformable mirror 3, which is an essential requirement of the present invention, will be described with reference to FIGS. 4, 5, and 6. FIG. 4 shows what is called an array type laser, which has conventionally been constructed by bundling a large number of laser generators in order to increase the laser output. At this time, the wavelength of each laser generator was made to be the same. In order to apply this to the present invention, it can be realized by arranging a plurality of lasers having different wavelengths. Array lasers are widely used as semiconductor lasers, and the wavelength of each laser can be changed by changing the energy gap required for excitation of each laser.

Next, the embodiment shown in FIG. 5 will be described. The laser beam output from the laser generator 1 has a specific oscillation wavelength width. The etalon plate has a filtering effect that selects the wavelength that passes through the etalon plate depending on its inclination with respect to the laser beam.

Therefore, by arranging the laser beams output from the laser generator 1 with the etalon plates 2a at different inclinations at positions corresponding to each region of the deformable mirror 3,
Laser beams of different wavelengths can be created.

Next, one embodiment will be described using FIG. 6. This uses a diffraction grating 2b to extract laser beams of different wavelengths. The diffraction grating 2b has the characteristic of reflecting the laser beam incident thereon at different angles for each wavelength. Utilizing this, the laser beams reflected from the diffraction grating 2b are adjusted by the mirror 2c so that the respective laser beams become parallel.Next, FIG. 7 shows an example of the deformable mirror 2.

This will be explained using FIG. FIG. 7 shows an embodiment of a split mirror type deformable mirror. A plurality of mirrors 3a connected to piezos 3b are arranged. The laser beam diameter is the same as the area of the mirror 3a, but the wavelength is changed for each beam. ΔQ shown in FIG. 7 is the optical path length difference. This ΔΩ
changes the phase of the individual laser beams.

Next, to explain an embodiment of the integrated mirror type deformable mirror shown in FIG.
Connect multiple b. By changing the stroke of each piezo 3b, the overall shape of the mirror 3a is changed. In this way, the deformable mirror 3 only needs to change the optical path length through which the laser beam passes, and the amount of displacement may be about ±2λ considering that the maximum phase difference of the laser is 2π.

Next, an embodiment in which the present invention is implemented using two different laser beams will be described with reference to FIGS. 9 and 10. In FIG. 9, 1a is a laser generator, and 1b is a laser generator placed on the XY scanner 10. The laser beam output from the laser generator 1a has a beam diameter that covers the entire surface of the deformable mirror 3, and is transmitted by the optical system 4 through the beam splitter 11 and the deformable mirror 3.
It is converged at the position of the target object 5. The diameter of the laser beam output from the laser generator 1b placed on the XY scanner 10 is made to match the area that can be controlled by one piezo of the deformable mirror 3. Now, the xY scanner 1o directs the laser beam from the laser generator 1b to the beam splitter 11.
is reflected at a specific area of the deformable mirror 3, and sent through the optical system 4 toward the target 5 at the same time as the laser beam from the laser generator 1a. At this time, the wavelengths of the two laser beams are different. Laser beam is target 5
The reflected wave 9 is detected by the means described in the first embodiment to detect the frequency component of the difference between the wavelengths or the amplitude of each wavelength, and then the laser beam of the laser generator 1b of the deformable mirror 3 is detected. Control the area hit by the beam. By performing the above operations by moving the XY scanner 10 and controlling the deformable mirror 3 while scanning the laser beam as shown in FIG. 10, the beam intensity at the target surface can be maximized.

According to this embodiment, the beam can be focused by the laser generator 1a for focusing and the laser generator 1b for control with different wavelengths, and the relationship between the wavelengths of the two laser beams is determined by the surface of the target object. Since it is invariant to state and movement, it is possible to focus the laser beam independently of the target object 5.

Next, a new embodiment utilizing the present invention will be described. FIG. 11 shows a laser processing machine according to an embodiment of the present invention.The laser processing machine of the present invention can be applied to cutting work of steel frames 13 and the like at construction sites and the like.

According to the present invention, since the laser beam can be condensed, if the beam is concentrated at one point, if a high-output laser generator is used, cutting can be performed using the thermal energy of the laser as in this embodiment. According to , structures can be processed using a laser processing machine located at a remote location, allowing work to be carried out in places that are difficult for humans to access.

Next, a laser guiding device using the present invention will be explained with reference to FIG. Airplane 1W on runway 18 at the airport
In order to guide the airplane 17 to the runway 18, a laser beam is transmitted on the optimum approach path of the airplane 17 to the runway 18, and the airplane 17 is provided with a sensor to detect it, and the airplane 17 is guided in the direction of the laser beam. According to the present invention, it is possible to suppress the diffusion of the laser beam due to atmospheric fluctuations, etc., so that the airplane 17 can be guided in the correct direction.

It goes without saying that the present invention can be applied not only to air as the medium through which the laser beam propagates, but also to other media such as water.

〔Effect of the invention〕

According to the present invention, since the laser beam can be focused in the medium, the laser beam intensity on the target surface can be increased by about two to one times depending on the state of the medium.

[Brief explanation of drawings]

FIG. 1 is a system diagram of a laser transmitter according to an embodiment of the present invention;
Fig. 2 is a control system diagram using a wavelength analyzer, Fig. 3 is an explanatory diagram showing the principle of the present invention, Fig. 4 is an explanatory diagram of an array type laser, and Figs. 5 and 6 are diagrams of a wavelength converter. 7 and 8 are explanatory diagrams of an embodiment of a deformable mirror, FIG. 9 is a system diagram of a laser transmitter according to an embodiment of the present invention, and FIG. 10 is a diagram of a laser beam scanning system. FIG. 11 is an explanatory diagram of an embodiment of a laser processing machine, and FIG. 12 is an explanatory diagram of an embodiment of a laser guiding device. 1... Laser generator, 2... Wavelength converter, 3...
Deformable mirror, 4... Optical system, 5... Target, 6...
- Photodetector, 7... Frequency discriminator, 8... Phase control circuit, 9... Reflected wave, 10... XY scanner, 11
...Beam splitter, 12...Wavelength analyzer, 1
3... Steel frame, 14... Crane, 15... Cutting section, 16... Laser processing machine, 17... Airplane, 18...
...Runway, 19...Laser guidance Figure 1 Figure 2 Figure 7 Cause Figure 4! Figure 5 Figure 6 Figure 9

Claims (1)

[Claims] 1. A laser transmitting device that converges and transmits a laser beam output from a laser generator using an optical system made of a combination of lenses or mirrors, comprising: means for converting the laser beam into a laser beam having a different wavelength for each region; means for independently changing the optical path length of the laser beam; and means for separating and detecting reflected waves from the imaging point of the laser beam for each wavelength; Means for detecting interference light between lasers having different wavelengths, and means for determining the optical path length of the means for changing the optical path length of the laser based on a signal for each detected wavelength or a signal of the interference light. A laser transmitter featuring: 2. In a wavelength converter that converts a laser beam into a different wavelength for each specific region, the laser beam output from the laser generator is provided with a plurality of etalon plates smaller than the laser beam,
A wavelength characterized in that the individual etalon plates are arranged with different inclinations with respect to the laser beam, the laser beam is passed through the plurality of etalon plates, and only the laser beam that has passed is output. converter. 3. In a wavelength converter that changes the wavelength of a laser beam, a diffraction grating and a mirror are provided, the incident laser beam is reflected on the diffraction grating, and the laser reflected at different angles for each wavelength is reflected by the mirror. A wavelength converter characterized by collimating lasers of individual wavelengths. 4. An array-type laser generator for generating laser, characterized in that a plurality of laser generators with different laser oscillation wavelengths are arranged. 5. In the laser transmitting device, a laser generator that generates a laser beam for condensing, a laser generator that generates a laser beam that is smaller than the laser beam and has a different wavelength, and means for overlapping the two laser beams. a means for changing the position of the laser beams having different wavelengths with respect to the focusing laser beam; a means for changing the optical path length of a specific region of the two laser beams; and a target of the focusing laser beam. A means for detecting reflected waves from an object, and an amplitude for each wavelength in the detection means, or
A laser transmitter comprising: means for detecting interference light; and means for changing the optical path length of the laser beams having different wavelengths based on a signal obtained by the means. 6. In a laser processing machine that uses laser energy to cut, weld, etc. metal or other objects, the laser beam is focused on a workpiece located at a distance from the laser processing machine to perform cutting, etc. A laser processing machine characterized by processing. 7. In a guidance device that guides an airplane to a runway at an airport, etc., transmitting a laser beam onto the airway entering the runway,
A laser guidance system characterized by comprising means for detecting the laser beam with a detector mounted on the airplane and controlling the traveling direction of the airplane in the direction of the laser beam.