JPH0133761B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a distance measuring method using a synthetic wavelength method.

The synthetic wavelength method, which is a method of distance measurement using interferometry, makes two beams of light with slightly different wavelengths enter a two-beam interferometer, and the interference fringes resulting from them are detected by the same detector. By passing the amplitude-modulated interference fringe signal generated when the mirror is swept through a squarer and a low-pass filter,
It generates a signal with a synthesized wavelength that is much longer than the original wavelength, and then determines distance by measuring the phase of this signal. The combined wavelength signal obtained by the above combined wavelength method is equivalent to an interference fringe signal due to long wavelength far infrared rays or millimeter waves, and unlike the interference of short wavelength light beams, it is not affected by atmospheric fluctuations, mechanical vibrations, etc. It is difficult to detect and is effective for high-precision distance measurement.

However, such a combined wavelength method has the following problems. That is, as a light source for the above-mentioned combined wavelength method, a carbon dioxide laser that oscillates a multi-wavelength light beam with good coherence is extremely promising, but this carbon dioxide laser requires continuous simultaneous oscillation of two wavelengths of laser light. is difficult. Therefore,
It is necessary to use two carbon dioxide lasers, but 2
In addition to being expensive to use multiple lasers, each laser varies the wavelength differently, so the accuracy of the combined wavelength generated based on those laser beams deteriorates as the wavelength is expanded.

The present invention solves these problems and uses a single laser, which is difficult to emit laser beams of two wavelengths simultaneously, but allows the laser to alternately emit laser beams of two wavelengths, and these laser beams can be combined. The present invention aims to provide a method that can perform distance measurement in the same way as when laser beams of two wavelengths are simultaneously and continuously oscillated by processing interference fringe signals based on .

In order to achieve the above object, the ranging method using the combined wavelength method of the present invention uses two laser beams of wavelengths λ ₁ and λ ₂ that are alternately oscillated at a fast cycle in one laser.
The laser beams are incident on a beam interferometer, and the interference fringes created by these laser beams are used to detect the first beams arranged at distance intervals to be measured.
Interference fringes based on the reflected light from the first and second reflecting mirrors are detected by separate detectors, and the output signals of these detectors are respectively processed by processing circuits with time constants longer than the oscillation period of the laser beam. By processing, the distance between the first and second reflecting mirrors is measured based on a composite wavelength signal that is sufficiently longer than the wavelengths λ ₁ and λ ₂ .

According to the distance measuring method of the present invention, it is possible to obtain a composite wavelength signal equivalent to the case where laser beams of two wavelengths are oscillated continuously at the same time, and the composite wavelength signal can be obtained even if the laser beams of two wavelengths are oscillated continuously. Because it is obtained by processing interference fringe signals from laser beams of two wavelengths, even if there are wavelength fluctuations in the two wavelengths of laser beams that are emitted, they cancel each other out. In combination with the fact that the distance measurement is performed using light, highly accurate distance measurement can be performed.

Next, the method of the present invention will be explained in more detail with reference to the drawings.

FIG. 1 shows the configuration of an apparatus used to carry out the present invention, in which 1 is a laser light source section, 2 is a wavelength stabilization section,
3 is a two-beam interferometer;
Distance measurement is carried out by alternately oscillating laser beams with different wavelengths at a fast cycle, and while the wavelengths of these laser beams are stabilized by a wavelength stabilization unit 2, they are incident on a two-beam interferometer 3, and the interference fringes generated there are detected and processed. I am trying to do this.

The laser light source section 1 includes one carbon dioxide laser 4, one of two mirrors 5 and 6 constituting a resonator in the laser 4 is attached to an electrostrictive element 7, and the electrostrictive element 7 is connected to a capacitor 8. This applies a square wave with a fast period from the oscillator 9 to the electrostrictive element 7, and when the voltage of the square wave is at a high level, a laser beam of wavelength λ ₁ is emitted, and when the voltage is at a low level, a laser beam is emitted. The configuration is such that the laser beams of wavelength λ ₂ are respectively oscillated, and thereby the laser beams of wavelengths λ ₁ and λ ₂ are oscillated alternately at a fast cycle, and these laser beams are projected toward the two-beam interferometer 3. I have to.

The wavelength stabilizing section 2 feeds back signals based on wavelength errors in the pair of laser beams to the input side of the laser light source section 1, thereby stabilizing the wavelengths to desired wavelengths λ ₁ and λ ₂ . It is constructed as something that does. Specifically, the laser light projected from the laser light source unit 1 is split into reflected light and transmitted light by the first beam splitter 11, and the reflected light is further divided into two parts.
a second beam splitter 12 for splitting into two beams;
and a reflecting mirror 13 are disposed on the optical path, and the laser beams of two wavelengths reflected by them are converted into a wavelength λ ₁ by choppers 14 and 15 which are driven in synchronization with the electrostrictive element 7 by a signal from the oscillator 9. and λ ₂ are detected by detectors 16 and 17, respectively, and then applied to the differential amplifier 20 through processing circuits 18 and 19 such as integrators or low-pass filters, thereby producing the above-mentioned results. By amplifying the wavelength error in a pair of single-wavelength laser beams and further applying the amplified signal to the electrostrictive element 7 via the next-stage high-voltage amplifier 21, a pair of laser beams oscillated by the laser light source section 1 is generated. The wavelength of the laser light is stabilized at the desired wavelengths λ ₁ and λ ₂ .

The laser light from the laser light source unit 1 whose wavelength has been stabilized in this way passes through the first beam splitter 11 and then enters the beam expander 23, where it is expanded and then sent to the beam splitter 24. Therefore, the light is divided into reflected light and transmitted light. The reflected light is reflected by a reference reflector 25 configured to be able to sweep, returns along the same optical path, and enters the beam splitter 24 again,
The light passes through it and heads towards the condensing lens 26. Also,
The transmitted light in the beam splitter 24 is reflected by the first and second reflecting mirrors 27 and 28, which are arranged at an interval of the distance L to be measured, and returns along the same optical path to be reflected by the beam splitter 24. , the interference light overlaps with the reflected light from the reference reflecting mirror 25 and is converged by the condenser lens 26. Of the interference fringes caused by the interference light, the first reflecting mirror 2
The interference fringes generated based on the reflected light from 7 are
The interference fringes reflected by the reflecting mirror 29 and detected by one of the detectors 31, and generated based on the reflected light from the second reflecting mirror 28, are directly detected by the other detector 32, and are detected by the other detector 32. Therefore, interference fringes caused by the laser beams of wavelengths λ ₁ and λ ₂ that are alternately oscillated are simultaneously detected by the respective detectors 31 and 32, respectively. The output signals from each of the detectors 31 and 32 are applied to processing circuits 33 and 34 such as an integrator or a low-pass filter having a time constant longer than the period of the square wave in the oscillator ₉ , _and The interference fringe signal is processed to be equivalent to the interference fringe signal obtained when two laser beams are continuously oscillated simultaneously. Further, the output signals from each of the processing circuits 33 and 34 are passed through squarers 35 and 36 and low-pass filters 37 and 38, thereby converting them into composite wavelength signals whose wavelengths are much longer than the original wavelengths λ ₁ and λ ₂ . After that, it is sent to a phase comparator 39, and from the phase difference of these combined wavelength signals, the first and second reflecting mirrors 2
A distance L of 7,28 is measured.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an apparatus used to implement the present invention. 3...2-beam interference type, 4...carbon dioxide laser,
27...first reflecting mirror, 28...second reflecting mirror,
31, 32...detector, 33, 34...processing circuit.

Claims (1)

[Claims] 1. Laser beams of wavelengths λ ₁ and λ ₂ that are alternately oscillated at a fast cycle by one laser are incident on a two-beam interferometer, and the interference fringes created by these laser beams are used to measure distances that are to be measured. The interference fringes based on the reflected light from the first and second reflecting mirrors are detected by separate detectors, and the output signals of these detectors are each detected by a time constant longer than the oscillation period of the laser beam. A combined wavelength method characterized in that the distance between the first and second reflecting mirrors is measured based on a combined wavelength signal that is sufficiently longer than the wavelengths λ ₁ and λ ₂ by processing in a processing circuit. Distance measurement method.