It has been shown that the absorptance of coated and uncoated germanium samples varies with surface state and ambient atmosphere. Absorption measurements made in air are up to 50% higher than identical measurements made under vacuum. The removable surface absorption on germanium has been shown to be due to both hydrocarbon and water layers, depending on the previous cleaning and ambient conditions. The residual surface absorption depends on the surface polishing procedure. Bulk absorption levels as low as 0.007 cm⁻¹ have been measured for freshly cleaned samples. Correlation between the surface condition and the laser induced damage thresholds at 10.6 μm indicates that the damage threshold should be significantly higher in vacuum.

Absorption and laser induced damage threshold measurements have been made on a range of CVD grown ZnSe substrates. Correlation has been shown between the grain size and the direction of measurement and the bulk absorption coefficient.