Measurement techniques for small absorption coefficients: recent advances.

A review is given of several newly developed methods for measuring low absorption losses in optical rnaterials. Transmission, emittance, and calorimetric techniques are described with special emphasis on how thermocouple and photoacoustic calorimetry can be used to determine both bulk and surface absorption simultaneously. The advantages and disadvantages of the various approaches are discussed, and estimates are given of the sensitivities that can be achieved with the different techniques. Finally, a new ac interferometric calorimetric method for measuring low bulk losses is proposed.