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    Glancing Incidence Absorption Measurements of Metal Mirrors

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    Glancing incidence absorption measurements are performed on bare Cu, Mo, Au, Al, and Ag mirrors, and on Al and Ag mirrors with a protective dielectric overcoat. Data is obtained for angles of incidence from 0° to ⩾89°. Wavelengths studied are 0.5 μm and 10.6 μm at both s and p polarizations. The absorption is measured using a photoacoustic calorimetry technique in which the transducer is attached directly to the back of the test mirror. Absolute calibration of the absorption data is obtained by using a ratiometer to independently measure the absorption at near normal incidence.

    The results are compared with the absorption predicted by Fresnel's equations for bare metals using values of n and k of the complex index of refraction measured by other sources. The absorption of a mirror at glancing incidence appears to be a sensitive function of its surface condition. New mirrors tend to agree with Fresnel's equations; while “old” mirrors have much higher absorption probably due to a layer of tarnish. The overcoated Al data deviates greatly from Fresnel's equations indicating that bare metal theory cannot be used and a thin film theory should be used instead. Representative results are given.


    absorption, Fresnel equations, glancing incidence, metal mirrors, overcoats, photoacoustic calorimetry, polarization

    Author Information:

    Kimura, WD
    Spectra Technology, Inc., Bellevue, WA

    Ford, DH
    Spectra Technology, Inc., Bellevue, WA

    Committee/Subcommittee: F01.02

    DOI: 10.1520/STP18748S