Abstract

Because of difficulties associated with field experiments, reported results on laser propagation in ice have been obtained primarily in the laboratory. To avoid changes that occur in optical characteristics of inhomogeneous natural ice when removed from its environment, we conducted laser propagation experiments in situ. We constructed an optical rail to allow a device (either an underwater laser or an underwater detector) to be positioned horizontally at known locations under the ice cover of a frozen lake. By mounting a picowatt detector on the rail, we mapped spatial profiles of a surface-mounted 2XNd:YAG laser beam pointing vertically down through the ice. Profiles were measured as a function of both detector depth and detector angle of view. After stripping layers from the ice surface, we measured additional spatial profiles of the downward-looking laser beam. By mounting an underwater 2XNd:YAG laser on the rail under the ice, we also mapped the spatial profile of an upward-looking laser. At the conclusion of the mapping experiments, blocks of ice near the test region were removed and studied to identify structural features in the ice that affect laser scattering. Spatial profiling results were analyzed to determine the optical properties of specific ice features.

© 1992 Optical Society of America