Laser Radar Analyses

General integral expressions for the power signal and power signal- to-noise ratio arising from laser heterodyne detection of a distorted optical phase front are derived. Specific analytical results for the efficiency of heterodyne detection are derived for a generalized transceiver system that include the effects of local oscillator and receiver aperture size and focal lengths as well as the amplitude radius of the Gaussian local oscillator. Efficiency effects are calculated assuming the phase front distortions arise from target scattering of a laser signal (speckle effects) and scintillation resulting from atmospheric turbulence. Specific numerical calculations of the signal-to-noise ratio efficiency illustrate the degradation in signal-to-noise ratio resulting from diffuse scattering from extended targets at close range and atmospheric turbulence effects at long range. These calculations indicate the requirement for a minimum receiving aperture size (commensurate with total received signal requirements) and a uniform local oscillator beam that underfills the target image (on the photocathode) for optimum laser radar efficiency.