HETERODYNE DETECTING METHOD UTILIZING GENERATION OF LIGHT PULSE TRAIN DUE TO SEMICONDUCTOR LASER

摘要

PURPOSE:To mix semiconductor laser with local oscillation signals having a slightly different modulation frequency of modulated current from a high frequency component and to remove noises due to leakage electric field generated by a power source and a transfer line by driving a semiconductor laser with intense modulated current when heterodyne detection is carried out using the semiconductor laser for a source of oscillation of the light high frequency signal. CONSTITUTION:High frequency f of a high frequency power source 21 of a reflectionless range finder which utilizes a heterodyne detecting method is superposed on the current from a DC bias power source 22 in a coupled circuit 23 to oscillate thus a semiconductor laser. After forming parallel beams generated here from pulse train 11 with a collimeter 12, an object 60 to be inspected is irradiated with the beams after adjusting the optical path of the beams with a reflecting prism 13. A part of the light from the object 60 to be inspected is collected with a condensing lens 70. A quick photodetector 30 is irradiated with the collected beams, and signals sensed by the photodetector 30 are mixed with signals having a frequency f0 from a local oscillator 50 in a frequency mixer 40. The signal having f0 frequency from the mixer 40 is frequency-multiplied, and supplied to a reference frequency mixer 82 together with the signal from the oscillator 50.