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    A Novel Technique for Investigating Impurity Initiated Short Pulse Laser Damage in Thin Films

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    A preliminary study has been conducted to investigate the effects of spot size on the laser induced damage threshold in thin films. Damage was produced by the interference fringes of two beams from a frequency-doubled Nd-YAG laser with a nearly Gaussian spatial profile. Fringes of spacing from 5 to 125μm were used on ZnS, ZrO2 and ThF4/ZnS films. The damage threshold and morphology were observed and are reported.

    Microscopic examination indicated that the appearance within a damaged region, which is as narrow as 1μm, is not different from that produced by a single beam whose half-intensity diameter is a hundred times larger. Interesting results concerning the relative importance of scratches and other defects were revealed by Nomarski microscopic observation of the damage morphology.

    It has been reported that laser damage to thin films is initiated primarily by small-size dielectric impurities and the dependence of the damage threshold on pulse length, film thickness, wavelength, and material investigated. In the present study it was observed that the damage threshold increased with decreasing film thickness in agreement with previous observations. However, there was no significant increase or decrease in threshold for the two-beam case over that for a single beam when the increased energy density due to interference effects is considered. In concert with previous observations it is concluded from the damage morphology and the absence of a spot size dependence that the source of damage initiation is impurities smaller than 1μm for these 5 ns pulse lengths.


    Laser damage, impurity-induced damage, thin films, damage threshold, ZrO, 2, ZnS, ThF, 4, .

    Author Information:

    Wiggins, TA
    The Pennsylvania State University,

    Walker, TW
    The Pennsylvania State University,

    Guenther, AH
    The Pennsylvania State University,

    Committee/Subcommittee: F01.02

    DOI: 10.1520/STP37018S