Transmitter-Size and Focus Effects on Scintillations*

Abstract

We present generalized numerical predictions of the effects of transmitter-aperture size and divergence on the on-axis scintillations of a laser beam propagating through a turbulent stmosphere, utilizing analytical results obtained from the literature. The sharp reduction of scintillation that has been predicted for a large, focused beam is shown to depend very critically upon the focus adjustment; small misadjustments result in increases by orders of magnitude. This also implies that diffraction-limited optics may be required. This requirement, together with the implications of turbulent beam-wander and spreading effects, suggest that the predicted reduction is of little practical significance. We also present the conditions necessary for obtaining point-source results in scintillation experiments.