A SEMIANALYTIC APPROACH FOR COHERENT LASER-RADAR SYSTEM EFFICIENCY - THE NEAREST-GAUSSIAN APPROXIMATION

A nearest Gaussian approximation (NGA) is proposed to approximate any shape for a single mode laser beam by a Gaussian shape. The applicatio n considered is a determination of the system efficiency in heterodyne coherent laser radar (HCLR). For an actual beam its NGA is defined by three parameters: the waist spot size and location, and an amplitude coefficient. These parameters are computed by a maximization of the no rm of the scalar product written for the actual and Gaussian beams. In the case of the truncated Gaussian beam, particularly relevant to HCL R, the waist location can be analytically calculated, and only two par ameters remain unknown: the waist spot size and amplitude coefficient. Using numerical applications, it is shown the NGA is in good agreemen t with Fresnel integral solution. The NGA combines a good accuracy and capability of analytical solutions. It can treat a variation in syste m efficiency owing to a misalignment angle between the transmitter and local oscillator.