STP799: Multiple-Shot Ultraviolet Laser Damage Resistance of Nonquarterwave Reflector Designs for 248 nm

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

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

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

    Carniglia, CK
    University of California, Los Alamos National Laboratory, Los Alamos, NM

    Pages: 17    Published: Jan 1983


    Abstract

    The damage resistance of multilayer dielectric reflectors designed for 248 nm has been substantially increased by use of nonquarterwave (QW) thicknesses for the top few layers. These designs minimize the peak standing-wave electric field in the high-index layers, which have proven to be weaker than the low-index components.

    Previous damage tests of infrared- and visible-wavelength reflectors based on these designs have produced variable results. However, at the ultraviolet wavelength of 248 nm, 99% reflectors of Sc2O3, MgF2, and SiO2 strongly demonstrated the merit of non-QW designs. Four sets of reflectors of each of four designs (all QW thickness; one modified-pair substitution; two modified-pair substitution; one modified pair plus an extra half-wave layer of Sc2O3) were tested for damage resistance with a KrF laser operating at 35 pps with a pulsewidth of 8 ns and spot-size diameter of 0.6 mm. Each of 50 sites were irradiated for 1000 shots or until damage occurred.

    On the average, the reflectors with one-modified-thickness pair had a 50% higher threshold (10 of 10 sites survived) than the all-quarterwave design. Addition of a second modified-layer pair resulted in no further increase in threshold but the saturation fluence (10 of 10 sites damage) was 110% higher. Reflectors with an additional half-wave of Sc2O3 had lower thresholds of the order of 10% as expected. The thresholds correlated best with the peak-field model, whereas the best model correlating the saturation fluences involved the sum of the upper two scandia layer thicknesses.

    Keywords:

    Damage thresholds, electric-field suppression, multiple shots, nanosecond pulses, nonquarterwave designs, scandium oxide, standing-wave electric fields, thin films, ultraviolet reflectors


    Paper ID: STP37260S

    Committee/Subcommittee: F01.02

    DOI: 10.1520/STP37260S


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