DE3144805C2 - Process for measuring relative movements by means of laser radiation according to the Doppler radar principle - Google Patents

Abstract

In the so-called heterodyne method for measuring relative movements by means of laser radiation according to the Doppler radar principle, two laser beams with a constant frequency difference are required. Using the interaction of transverse laser modes, laser beams with a constant frequency difference are generated and decoupled in partial areas of a single laser.

Description

1. Tilting and / or three-dimensional deformation of the resonator mirror,

2. change in resonator length,

3. all possibilities of mechanical deformation the resonator geometry, e.g. B. Changes in cross-section and bending of the plasma tube,

4. Deformation of the active laser medium,

5. Change of the resonator symmetric. z. B. reflectivity of the plasma tube,

so 6. Combination of these measures.

f "(fs + Vo) -

Since vzf can be measured and / Sv. is known, the relative speed can be determined from (1) and (2):

c {v _ZF -Av)
2 · v.

Depending on the value of the difference Av = * vs — vlo, a distinction is made between two methods:

Av = 0
Av ψ 0

In addition, the radiation of the individual partial areas of the mode image has different optical - vlo) + vd = Av + vd (2) carrier frequencies, whereby the corresponding difference frequencies can be set over a wide range by the above measures.

With the help of simple methods, see the patent specification DE-PS 3143 056, "Laser with intensity modulation", the difference frequencies can be stabilized in the long term to a range of a few Hz. The short-term fluctuations of the laser have almost the same effect on both laser beams, so that in this respect too the new method is clearly superior to the previous method. Due to the simple stabilization measures by means of control loops, the measuring accuracy of the apparatus can be increased by several orders of magnitude without significant additional effort.
The advantages of the invention over the previous

Homodyne method
Heterodyne method

Procedure lie in the fact that with a fraction the previously necessary technical effort a significantly higher measurement accuracy in the determination can be achieved by relative speeds.

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Claims (2)

Patent claims: 1. Method for measuring relative movements by means of laser radiation according to the Doppler radar principle, using a laser oscillator to emit a transmission signal (ys) and output an oscillator signal (yLo) with a constant frequency difference (Av) (= so-called heterodyne method), characterized by the use of a waveguide or TEA lasers with devices for targeted influencing of the parameters of the laser resonator, whereby laser beams with a tunable, constant frequency difference (Av) are generated and decoupled by utilizing the interaction of transverse laser modes in partial areas of the laser oscillator. 2. The method according to claim 1, characterized in that the frequency difference (Av) of the coupled-out radiation is iangzeiisiabilisiert by control loops. The invention relates to a method for measuring Relative movements by means of laser radiation according to the Doppler radar principle, according to the preamble of the claim 1. The use of laser radiation for the measurement of relative speeds is known, A. Javan, EA BaIHk, WL Bond, J. Opt. Soc. Am, vol. 52, no. 1, pp. 96-98 (1962). The measurement is based on the principle of optical superimposition reception. A laser beam (transmission beam!) With frequency vs hits a moving object. This scatters a fraction of the transmitted intensity onto the receiving optics. In accordance with the relative speed vr of the object to the transmitting / receiving apparatus, the frequency ve of the backscattered radiation (received signal) is Doppler shifted by the amount "O". The following applies: ^v n 2v " c = speed of light If the optical received signal Ve = Vs + Vd is superimposed on an optical detector with the beam of frequency vlo of a local oscillator, which has a frequency spacing Av from the transmitted beam, an electrical signal of the intermediate frequency vzp results: Compared to the homodyne process, the heterodyne process offers considerable advantages such as lower noise. However, it is technically complex. Either two different lasers are used, which are stabilized by extensive measures in such a way that Av remains constant, or the laser intensity of a laser is split into two partial beams (transmit beam and LO beam) by suitable modulation external to the resonator (electro-optical or acousto-optical) of a partial beam the necessary frequency offset Av is achieved. As a rule, these modulation methods are very complex and they reduce the usable radiation power.
The invention is based on the object of realizing the measurement of relative movements according to the heterodyne method with less technical effort. According to the invention, this object is achieved with a method solved as it is characterized by claim 1. Developments of the invention are in the Described subclaims. The invention is based on the utilization of the interaction or spontaneous coupling of transverse laser modes, as described in the patents DE-PS 31 25 544 and DE-PS 31 43 057, which deal with "waveguide and TEA lasers". Based on this Interaction of transversal laser modes can be obtained from a single laser resonator by a targeted influence (e.g. fading out the partial beams, using decoupling mirrors with different reflections) with suitable difference frequencies for the heterodyne method.
As described in patent specification DE-PS 31 43 057 for the special case of waveguide and TEA lasers, the laser radiation can be changed in terms of amplitude, frequency and polarization by deliberately changing the parameters of the laser resonator. Such measures are