LASER DISTANCE MEASURING INSTRUMENT

PURPOSE:To measure the movement distance of a body which passes at right angles to the irradiation direction of a laser beam with high accuracy without touching the body by converting scattered light from the body into an electric signal. CONSTITUTION:The irradiating laser light from a laser light source 1 is split by a beam splitter 2 and one laser beam is shifted in frequency by Bragg cells 3 and 4. Then the 1st and 2nd laser beams irradiate one point by an optical means, so interference fringes are formed to obtain the scattered light. This scattered light is converged and converted 17 photoelectrically to obtain a signal of frequency corresponding to the moving speed of the interference fringes and the conveyance speed of the body. A driving frequency detecting means detects the frequency difference between the laser beams to generate a reference signal and the photoelectric conversion output is supplied to 1st and 2nd change point detecting circuits of a frequency difference detecting circuit 20 as a signal corresponding to the movement distance of the body. Then the movement distance of the body can be measured according to output pulses of the detecting circuit 20.