Doppler Optical Radar and the Heterodyne Measurement of Oscillating Systems

摘要

The measurement of oscillating systems is presented as a prelude to an investigation of Doppler optical radar. The radiation from a single-mode gas laser is used successfully by Doppler optical heterodyne techniques to measure the displacement and velocity waveforms of a moving-coil loudspeaker and a piezoelectric transducer. Vibrations as small as a twentieth of a wavelength (0.000001 cm) and velocities as low as .1 cm per second are measured. A simple method of synchronization is shown to allow convenient measurement of target tilt or distortion as well as the velocity at any point on the target's displacement waveform. Theoretical considerations covering the statistical nature of radiation from thermal light sources are presented and used to demonstrate the feasibility of mixing either independent or correlated thermal light beams. Laser sources are shown to exhibit qualities (specifically narrow bandwidth and high degeneracy values) not characteristic of thermal sources but which are necessary for Doppler optical heterodyning over long target ranges. While offering resolution and directional advantages over conventional microwave radar systems, Doppler optical radar is restricted by target jitter and diffuse target reflectance which increase signal bandwidth and destroy coherence. A study is made of these effects. (Author)