MEASUREMENT OF VERY LOW OPTICAL-ABSORPTION COEFFICIENTS IN BULK MATERIALS

The measurement of very low optical absorption coefficients in bulk materials is described with emphasis on adiabatic laser calorimetry with long rod samples. Bulk absorption coefficients lower than 10** minus **5 cm** minus **1 have been achieved in both crystals and glasses using this technique. At extremely low levels, both sensitivity and discrimination between surface and bulk sources of absorption is required. The technique described is perhaps the best way at the present time of studying such low level absorptions.