Abstract: Laser Doppler anemometer with a wavelength-stabilized laser diode (1) whose beam after splitting (7) is so concentrated in a definite area (9) of a particle-containing flow of a fluid with the velocity (17) that in this area (9) an interference fringe pattern is produced, and with at least one semiconductor photodiode (13) on which the laser beams (10, 11) progressing from the area (9) are refocussed after elimination of scattered light fractions by a scattered light trap (diaphragm stop) (14), for the detection of the difference signal I between incident light intensity I.sub.o and scattered light intensity I.sub.scatter which the particles contained in the fluid emit into the whole solid angle 4.pi., where I=I.sub.o -I.sub.scatter. By detection of the laser beam of the intensity I which is modulated with the Doppler frequency after having passed through the point of measurement (9), the whole light intensity I.sub.scatter emitted by the particle into the solid angle 4.pi.

Abstract: A laser Doppler anemometer with at least two laser beams pass to a region of a fluid flow containing particles. The scattered light is frequency shifted by the Doppler frequency resulting from the flow speed. The construction is very compact and permits a high signal-to-noise ratio for the measurement signals. The laser beams consist of high-frequency pulses, the frequency of the pulse sequence of which is a multiple of the Doppler frequency.

Abstract: A laser Doppler anemometer includes at least a first and second laser source, an optical system for directing laser beams from the sources to a specific region of a fluid flow containing particles in order to produce a virtual interference fringe pattern and at least one photodetecter positioned for receiving the scattered light from the flowing fluid. At least one of a temperature regulation and current regulation circuit is provided for stabilizing the wavelength of at least one of the laser sources. The first and second laser sources are set to different emission wavelengths and a regulating circuit is provided for maintaining the difference frequency between the first and second sources constant. The difference frequency is in turn utilized to control the temperature regulation and/or current regulation circuit for at least one of the laser sources to achieve stabilized operation thereof.

Abstract: In a device for measuring the speed of moving light-scattering objects by means of laser beams, with which a periodic intensity distribution (4) is produced at the measuring point (3), and by means of a detecting device (5, 7; 8, 9, 10) for light scattered by the object, it is possible to produce the periodic intensity distribution in a simple fashion with a laser diode array (1) in which a plurality of laser diodes are arranged at a defined separation from one another. Light emitted by the laser diode is focussed at the measuring point (3) with a focusing optical system (2). In addition, when measuring speed it is possible to discriminate direction by arranging the laser diode array (1, 13) such that no emission occurs in at least one such location (11') of the laser diode (11), so that an asymmetric intensity distribution is produced at the measuring point (3).