SEDL / STP / STP689-EB / STP39099S

A Comparison of Bulk and Surface Absorptions in NaCl and KCl between 9.2 and 10.8 µm

Vora, H
Honeywell, Inc., Corporate Research Center, Bloomington, MN

Ohmer, MC
Air Force Materials Laboratory/LPO, Wright-Patterson AFB, Ohio

Stoebe, TG
University of Washington, Seattle, WA

Pages: 9    Published: Jan 1979

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Abstract

Tunable CO² laser calorimetry has been used to study the wavelength dependence of optical absorption at 16 different wavelengths between 9.2 and 10.85 µm in NaCl and KCl. Samples prepared on a small scale using the reactive atmosphere process (RAP) growth, as well as samples cut from large diameter ingots prepared commercially for high-power CO² laser windows, have been investigated. A differentiation between the bulk and surface absorption has been made in several cases using long bar samples. The measured bulk absorption in the best RAP-grown NaCl crystal is intrinsic over the entire wavelength range from 9.2 to 10.85 µm, showing bulk absorption values near 9×10^-4 cm^-1 at 10.6 µm and 1.4×10^-4 cm^-1 at 9.2 µm. The best KCl shows bulk absorption values near 9×10^-5 cm^-1 at 10.6 µm and 4×10^-5 cm^-1 at 9.2 µm; these values are above the expected intrinsic limit due to residual absorption caused by the presence of at least two bulk impurities, possibly ClO^3- and ClO^2-.