Shipboard Atmospheric Propagation Measurements

Directing a high-power laser (HPL) beam through the atmosphere onto a distant target is limited by atmospheric absorption of the laser light, which causes thermal blooming and wavefront distortions that are difficult to correct. In the near-IR there are three atmospheric windows, in which atmospheric absorption is relatively weak, at wavelengths near 1 micron, 1.6 micron and 2.2 microns. The selection of the operating wavelength and requisite power level of an HPL that is designed to be directed through the atmosphere requires detailed measurement of atmospheric absorption as a function of wavelength by both molecules and aerosols. SRL proposes to develop an absorptometer that accurately measures the absorption of laser beams in the atmosphere in these windows and is insensitive to scattering losses. The instrument, which will utilize sensitive interferometry, will be capable of measuring both gas constituents and naturally occurring aerosols in both laboratory anid field experiments, with the objective of delivering a measurement system that can be used on a shore-based site and on a seagoing vessel. In Phase I SRL completed a conceptual formulation and design of a system that can measure the absorption of a laser beam by atmospheric gases and naturally occurring aerosols in a laboratory and maritime environment. In Phase II SRL will assemble, test and deliver a robust aerosol-laden-air measurement system.