Temperature dependence of surface and bulk absorption in NaCl and KCl at 10.6 μm

The optical-absorption coefficient $\beta$ has been measured in NaCl and KCl at 10.6 μm from 100 to 300 K using low-temperature, C${\mathrm{O}}_2$ laser calorimetry. From the total absorption, both bulk and surface contributions were extracted. Bulk $\beta \text{'}\mathrm{s}$ of 1.4 × ${10}^{-4\mathrm{}}$ and 3 × ${10}^{-5\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$ (upper limit) were measured for NaCl and KCl, respectively, at 100 K and 10.6 μm. The temperature dependence of the bulk values are compared to several recent multiphonon theories. The temperature dependence of the surface absorption is also presented and discussed for NaCl and KCl.