Abstract: A method and apparatus for stabilizing the frequency at which a laser cavity oscillates comprising a passive system which provides a plurality or continuum of optical paths of differing lengths. The various paths correspond to differences in mode parameters in the cavity, and involve compensating changes in polarization, beam direction, beam divergence, and the like, in exchange for a constant optical path length in the laser cavity. The unchanging optical path length results in a stable frequency of oscillation despite physical changes in the cavity which might otherwise alter that path length.

Abstract: A laser source is operated continuously and modulated periodically (typicy sinusoidally). A receiver imposes another periodic modulation on the received optical signal, the modulated signal being detected by an array of detectors of the integrating type. Range to the target determined by measuring the phase shift of the intensity modulation on the received optical beam relative to a reference. The receiver comprises a photoemitter for converting the reflected, periodically modulated, return beam to an accordingly modulated electron stream. The electron stream is modulated by a local demodulation signal source and subsequently converted back to a photon stream by a detector. A charge coupled device (CCD) array then averages and samples the photon stream to provide an electrical signal in accordance with the photon stream.