DE3144805A1 - Method for measuring relative movements by means of laser radiation in accordance with 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 having a constant frequency difference are needed. Utilising the interaction of transverse laser modes, laser beams having a constant frequency difference are generated and coupled out in part areas of a single laser.

Description

Method for measuring relative movements by means of laser radiation According to the Doppler radar principle 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 claim 1.

The use of laser radiation for measuring relative speeds is known to A. Javan, E.A. Ballik, W.L. Bond, J. Opt. Soc. At the. 52, 96 (1961).

The measurement is based on the principle of optical superimposition reception. A laser beam (transmission beam) with the frequency Lts hits a moving object. This scatters a fraction of the transmitted intensity onto the receiving optics. According to the relative speed v R of the object to the transmitting / receiving apparatus, the frequency tE of the backscattered radiation (received signal) is "Doppler shifted" by the amount. c P Speed of light If the optical received signal tE tS + D is superimposed on an optical detector with the beam of frequency bLO of a local oscillator, which has a frequency separation au from the transmitted beam, an electrical signal of the intermediate frequency tZF #ZF = (#S + #D) - #LO = (#S - #LO) + #D = ## + #D (2) 5 Since #ZF can be measured and AZ is known, the relative speed can be determined from (1) and (2) become: c (YzF - VR 2-- (3) S. Depending on the value of the difference ## = #S - #LO, a distinction is made between two methods ## = 0 homodyne method ## # 0 heterodyne method Compared to the homodyne method, the heterodyne method offers considerable advantages such as lower noise.

However, it is technically complex. Either you use two various lasers, which are stabilized by extensive measures so that ar remains constant, or the laser intensity of a laser is split into two partial beams (Transmit beam and LO beam) split. By suitable modulation external to the resonator (electro-optical or acousto-optical) of a partial beam one achieves the necessary Frequency offset a t. As a rule, these modulation methods are very complex and reduce the usable radiation output.

The invention is based on the object of measuring relative movements to accomplish according to the heterodyne process with less technical effort.

According to the invention, this object is achieved with a method such as it is characterized by claim 1. Developments of the invention are in the Described subclaims.

The invention is based on the exploitation of the interaction or spontaneous Coupling of transverse laser modes, as described in patent applications P 31 25 544.2 and P 31 43 057.0 "Waveguide and TEA-LaserW. Based on this Interaction of transversal laser modes can be achieved through a specific influence (e.g. masking out the partial beams, using decoupling mirrors that are locally different Reflection). from a single laser resonator laser beams with suitable difference frequencies for the heterodyne method can be obtained.

As in the patent application P 31 43 057.0 for the special case of Waveguide and TEA laser described, the laser radiation can be targeted Change in the parameters of the laser resonator with regard to their amplitude, frequency and polarization can be changed. Such measures are 1. Tilting and / or three-dimensional Deforming the resonator mirror, 2. Changing the resonator length, 3. All possibilities the mechanical deformation of the resonator geometry, e.g. changes in cross-section and bending of the plasma tube, 4th .. deformation of the active laser medium, 5th modification resonator symmetry, for example the reflectivity of the plasma tube, 6. Combination of these measures.

In addition, the radiation from the individual areas of the Modesbildes different optical carrier frequencies, with the corresponding Difference frequencies through the above measures in wide Ranges are adjustable.

With the help of simple procedures, compare patent application P 31 43 056.2 "Lasers with intensity modulation" can use the difference frequencies up to a few Hz bandwidth are long-term stabilized. The short-term fluctuations of the Lasers have almost the same effect on both laser beams, so that In this respect, too, the new process is clearly superior to the previous process is. Due to the simple stabilization measures by means of control loops, the Measurement accuracy of the apparatus by several orders of magnitude without significant additional effort increase.

The advantages of the invention over the previous methods are in the fact that with a fraction of the previously necessary technical effort a considerably higher measurement accuracy when determining relative speeds can be reached.

Claims (3)

Patent claims: Method for measuring relative movements by means of Laser radiation according to the Doppler radar principle, using a laser oscillator for emitting a transmission signal (#S) and emitting an ossillator signal (wLO) with constant frequency difference (# #) (- so-called heterodyne method), thereby G e -k e n n n n z e i c h n e t that by exploiting the interaction of transversal Laser modes in partial areas of the laser oscillator Laser beams with constant frequency difference (ß t) are generated and decoupled. 2. The method according to claim 1, characterized in that g e -k e n n z e i c h n e t that by deliberately influencing the parameters of the laser resonator, the frequency difference (b) the coupled-out radiation. is set. 3. The method according to claim 1 or 2, characterized in that g.e k e n n z e i c h n e t that the frequency difference (ay) of the decoupled radiation by control loops long-term stabilization