A new method is presented for measuring the absorptance of evaporated metal films as a function of wave-length with a possible precision of ±1.4%. The sample consists of a temperature-sensitive quartz crystal which is plated on both sides with the metal film. The small temperature rise of the plated crystal due to the energy absorbed from the incident beam of radiation is measured by monitoring the frequency change of the quartz crystal when it is driven in an oscillator. The absorptance, relative to a black surface, is determined from frequency rates at a particular temperature as the crystal goes through a heating and cooling cycle. Results are given on the absorptance of an aluminum film at room temperature as a function of wavelength between 0.45 and 2 µ.
W. M. BRANDENBERG, O. W. CLAUSEN, and D. MCKEOWN, "High-Precision Method for Measuring the Absorptance of Evaporated Metals," J. Opt. Soc. Am. 56, 80-85 (1966)