High-Energy Laser-Assisted Imaging Through Vaporizing Aerosols

The degradation of image quality due to multiple scattering in a turbid medium is analyzed under various conditions of illumination. The emphasis is on the forward-peaked multiple scattering effects, which can adequately be described by the small-angle approximation. In the case of incoherent illumination, the modulation transfer function (MTF) can be given explicitly both in the low- and high-frequency limits. For scattering with smaller degree of anisotropy, the MTF should be computed numerically by considering solutions to the equation of radiative transfer with a line or point source. As the beam power increases, the turbid medium becomes modified by its interactions with the beam, thus affecting the image resolution. In this nonlinear transport regime (flux levels of the order of 106 W/cm2 and higher) the propagation leads actually to beam narrowing. In the context of the imaging problem, an apparent paradoxical situation in which the image of a point source narrows down as the high-energy laser (HEL) beam propagates is discussed.