Table 2. Comparison of Reflector Materials for CO2 Lasers
 Material Index of Refraction Fresnel Reflectivity Fabry-Perot Reflectivity  Absorptivity inverse cm Hygroscopic
 NaCl crystal 1.490 0.039 0.145
less than 0.10
Yes
 KCL crystal 1.454 0.034 0.127 less than 0.01 Yes
BaF2 crystal 1.420 0.030 0.113  0.077 Slightly
 KRS-5 2.380 0.167 0.490 0.020 Slightly
 Irtran-2  2.190 0.139 0.429 about 0.55  No
 Irtran-4  2.400 0.170 0.497 about 0.10  No
 Germanium 4.000 0.360 0.779  about 0.07  No