The receiving efficiency η as a function of range z is investigated for pulsed coherent lidars using a theory that relates η(z) to the transmitted laser intensity and the point-source receiving efficiency ηs(r,z). The latter can be calculated either by a forward method, or by a backward method that employs the back-propagated local oscillator (BPLO) approach. The BPLO method is efficient and accurate provided that cascaded diffraction effects inside the lidar system are properly taken into account. The theory is applied to the ideal case to examine the optimization of the system when both transmitted and BPLO fields at the antenna are Gaussian, including optimum telescope aperture.
Yanzeng Zhao, Madison J. Post, and R. Michael Hardesty, "Receiving efficiency of monostatic pulsed coherent lidars. 1: Theory," Appl. Opt. 29, 4111-4119 (1990)