STP759

    Dependence of Metal Mirror Damage Thresholds on Wavelength, Material, Pulse Length, and Preparation Method

    Published: Oct 1981


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    Abstract

    Multithreshold pulsed laser-damage characteristics of precision diamond-machined Cu, Ag, and Au mirrors have been determined at 10.6, 3.8, 2.7, and 1.06 μm. The effect of pulse length has been examined at 10.6 μm by comparing previously reported results obtained using a 100-nsec TEA laser pulse with new results using a 2-μsec pulse from a hybrid TEA laser. The pulse lengths at 3.8 and 2.7 μm are nominally 100 nsec, while that at 1.06 μm is 9 nsec. Spatial intensity distributions are very nearly Gaussian at all wavelengths with e−2 focal spot diameters ranging approximately from 200 μm at 10.6 μm wavelength to 50 μm at the shorter wavelengths. Melt thresholds were calculated from one-dimensional heat flow considerations with a correction for finite focal spot size. Laser waveforms are accurately modeled, and temperature-dependent absorption based on Drude theory is used. Calculated values for Ag are in excellent agreement with experiment, except at 1.06 μm, while calculated values for Cu and Au are in good agreement at 10.6 μm only. An unusually large discrepancy at 3.8 μm suggests a non-Drude-like absorption mechanism that is enhanced by the multipeaked nature of the waveform at this wavelength. Defect-related damage at submelting fluences has also been studied at the longer 10.6-μm pulse length on Cu mirrors representing a variety of preparation methods. Comparative evaluation of damage characteristics has resulted in identification of two new approaches to improving resistance to defect damage.

    Keywords:

    Cold work, crystalline disorder, defect damage, diamond-machined mirrors, Drude absorption, electron-beam melting, laser waveform, melt threshold, metal deposition, pulsed laser damage, slip threshold, thermal diffusion length, thermal stress


    Author Information:

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

    Decker, DL
    Michelson Laboratory, Physics Division Naval Weapons Center, China Lake, California

    Seitel, SC
    Michelson Laboratory, Physics Division Naval Weapons Center, China Lake, California

    Soileau, MJ
    Michelson Laboratory, Physics Division Naval Weapons Center, China Lake, California


    Paper ID: STP37010S

    Committee/Subcommittee: F01.02

    DOI: 10.1520/STP37010S


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