Calorimeter to Measure the 10.6-microm Absorption of Metal Substrate Mirrors

We have designed, constructed, and tested an instrument to calorimetrically measure the 10.6-microm absorption a of high reflectivity metal-substrate mirrors. Optical, electrical, and thermal design considerations will be discussed. The technique of absorption measurement, including the in situ heat capacities, the reflected laser light to an accuracy of +/-4%, and the simplified data reduction technique will be discussed. From our error analysis we conclude that our accuracy is +/-0.1alpha and has a precision of 0.0005. Comparative measurements on the same mirrors by different reflectivity and absorption devices and extensive absorption data on state-of-the-art 10.6-microm metal-substrate mirrors will be presented. The best absorption that we have measured is 0.0010 for a gold-coated multidielectric enhanced mirror.