The geometrical-optics approximation of light scattering by a transparent or absorbing spherical
particle is extended from plane wave to Gaussian beam incidence. The formulas for the calculation of the phase of each ray and the divergence factor are revised, and the interference of all the emerging rays is taken into account. The extended geometrical-optics approximation (EGOA)
permits one to calculate the scattering diagram in all directions from 0° to 180°. The intensities of the scattered field calculated by the EGOA are compared with those calculated by the generalized Lorenz–Mie theory, and good agreement is found. The surface wave effect in Gaussian beam scattering is also qualitatively analyzed by introducing a flux ratio factor. The approach proposed is particularly important to the further extension of the geometrical-optics approximation to the scattering of large spheroidal particles.
© 2006 Optical Society of America
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