Measurement Of Absorption Losses Of Optical Thin Film Components By Photothermal Deflection Spectroscopy

For the development of optical coatings (as high power laser mirrors) of higher and higher performances, it is necessary to use more and more powerful characterization means for optical thin films. The highly sensitive and simple technique of Photothermal Deflection Spectroscopy (P.D.S.) gives the absorption losses down to ultra low level. We show that this method can be applied to transparent single layers. Techniques used for photothermal signal calibration are presented. Photothermal signal versus wavelength for absorbing layers (extinction coefficients from some 10-3) is compared with absorption spectra obtained by classical spectrophotometry. Experimental results are given which show the sensi-tivity of the method. Extinction coefficients that do not exceed some 10-7 can be measured. P.D.S. can also give absorption losses for multilayer coatings. Some results on narrow band filters are presented.