STP799

    Laser Damage Results and Analyses for Ultraviolet Reflectors Under Multiple-Shot Irradiation

    Published: Jan 1983


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    Abstract

    In a continuing program intended to evaluate and optimize multi-layer dielectric reflectors for the ultraviolet, additional results are reported.

    Standard test conditions at the 248 nm KrF* wavelength are a nominal pulsewidth of 10 ns at a 35 Hz pulse repetition frequency. The 0.6 mm mean spot diam (Io/e2) is effectively increased by testing ten sites at each fluence, with each surviving site irradiated for 1000 shots. In this manner, 50 to 100 sites are tested on each reflector. By plotting the fraction of sites which damaged (%) vs laser test fluence (J/cm2) and employing a linear regression fit to the data, a threshold (0% intercept) and an upper limit (100% intercept) are obtained. Emerging correlations between the slope of the data and physical properties of the coatings are discussed.

    We have previously reported damage thresholds averaging 1.5 J/cm2 with a high of 3.0 J/cm2 for a ThF4/Cryolite reflector. Presently, we routinely observe thresholds of 3.0 J/cm2 up to a high of 5.5 J/cm2 for oxide films, particularly those employing Al2O3 or Sc2O3 as the high-index component.

    As an initial attempt to ascertain the possible effect of pulse repetition rate, some samples were tested at both 35 pps and 2 pps. Within our experimental uncertainty, no difference in threshold was observed.

    Keywords:

    fluoride coatings, KrF* lasers, multiple-shot laser damage, oxide coatings, repetition-rate effect, spotsize effect, ultraviolet reflectors


    Author Information:

    Foltyn, SR
    University of California, Los Alamos National Laboratory, Los Alamos, NM

    Newnam, BE
    University of California, Los Alamos National Laboratory, Los Alamos, NM

    Jolin, LJ
    University of California, Los Alamos National Laboratory, Los Alamos, NM


    Paper ID: STP37259S

    Committee/Subcommittee: F01.02

    DOI: 10.1520/STP37259S


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