STP799: Laser Desorption Analysis of H2O and Other Contaminants from Optical Surfaces

    Porteus, JO
    Michelson Laboratory, Physics Division Naval Weapons Center, China Lake, California

    Faith, WN
    Michelson Laboratory, Physics Division Naval Weapons Center, China Lake, California

    Allen, SD
    Michelson Laboratory, Physics Division Naval Weapons Center, China Lake, California

    Pages: 7    Published: Jan 1983


    Abstract

    Contamination at surfaces and interfaces is known to cause lowered damage threshold in high power laser optical components; therefore, it is important to be able to identify and measure the amount of adsorbed species. A technique has been developed for detecting water and other adsorbed molecules on optical surfaces at incident intensities below the damage threshold. A pulsed laser is focused onto the optical surface of interest in a UHV chamber. The laser energy absorbed in the surface layer causes desorption of the contaminants. Detection and identification of the desorbed species are via a quadrupole mass analyzer. As water and other contaminants such as hydrocarbons are strong optical absorbers in the 2.8- to 3.8-μm wavelength region, an HF/DF laser was chosen for the initial investigation. H2O, OH, and other species have been observed from both coated and uncoated optical surfaces. Surface mapping of adsorbed H2O with a 121μm focal spot shows considerable variation with spatial position. This effect may be associated with surface microcracks and other defects which may precipitate laser damage. Possible applications are characterization of laser optical components and laser cleaning of optical surfaces prior to film deposition.

    Keywords:

    laser conditioning, laser-induced desorption, optical surfaces, selective damage, surface contamination, surface defects, water desorption


    Paper ID: STP37251S

    Committee/Subcommittee: F01.02

    DOI: 10.1520/STP37251S


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