Optimal truncation and optical efficiency of an apertured coherent lidar focused on an incoherent backscatter target

Two earlier computations of the optimal truncation of Gaussian beams for a simple, focused, coherent lidar that used an incoherent backscatter target with identical circular transmitter and receiver apertures differ because they refer to different receiver geometries. The definitions of heterodyne and systemantenna efficiencies are reviewed in light of the discrepancy and are used to compare the optical performance of systems with apertures illuminated by beam profiles that are not Gaussian. The heterodyne efficiency is less than 0.5 for all cases considered here.