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Chemically vapor-deposited ZnSe exhibits outstanding
properties in the infrared (IR) and has been established as
a prime material candidate for IR transmitting applications.
The purpose of this paper is to present and evaluate data on
both the surface and the bulk absorption of commercially
available ZnSe, over the entire wavelength and temperature
range of current interest. This investigation is based on
spectral emittance measurements that were carried out by
Stierwalt at the Naval Ocean Systems Center and on in-house
transmission spectroscopy performed in the context of a
fur-window development program. Surface effects can be
felt at wavelengths as high as 14 um and usually predominate
at wavelengths of less than 8 urn, even for fairly thick
specimens. Fractional surface absorptions are temperature
independent from about 200 to 400 K, which masks the
behavior of the bulk absorption, and can be fitted to a
Fourier series, for wavelengths of 3.5 to 13.5 urn. Bulk
absorption coefficients (nv) are strongly dependent upon
temperature as well as wavelength but can be approximated by
means of two bivariate polynomial expressions that yield
"recommended" values. At wavelengths X 10 urn, v always
decreases with increasing temperature; it is shown that a
wavelength independent Debye-Waller factor provides a
correct description of the temperature dependence, thus
pointing to IR-active localized modes. At wavelengths X
14 urn, V always increases with rising temperature and
exhibits a temperature-dependence pattern as predicted for
3- and 4-phonon summation processes. Finally, an analysis
of the temperature dependence of j at 10.6 urn demonstrates
that the intrinsic lattice-vibrational contribution to bulk
absorption at the CO2-laser wavelength should be close to
4x1Ocrn, in accord with the results of earlier lasercalorimetry
tests performed on exceptionally pure ZnSe.
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