PHOTOTHERMAL ABSORPTION MICROSCOPY OF DEFECTS IN ZRO2 AND MGF2 SINGLE-LAYER FILMS

Photothermal displacement microscopy has been used for the characteriz ation of ZrO2 and MgF2 single-layer thin films to detect absorption in homogeneities at X = 514 nm. Images are presented for films of lambda/ 2, lambda, and 2lambda optical thickness deposited on BK7 glass and SQ 1 quartz substrates. Applying modulation frequencies ranging from 1 to 100 kHz a lateral resolution of several micrometers was obtained. We found that the size and density of the absorption inhomogeneities as w ell as absorptance depend strongly on the deposition process and weakl y on the substrate material. No dependence on thin film thickness was found. The apparent defect density varies with the modulation frequenc y demonstrating the capability of the photothermal method to localize absorption in various depths of the thin film. Defect densities derive d from the photothermal measurements are compared with results from to tal integrated light scattering (TIS) experiments performed on various samples at lambda = 632 nm. TIS intensities for MgF2 films on glass s ubstrates were about one order of magnitude smaller than those from fi lms on quartz. The latter revealed strong long-range (1-mm) variations of the light scattering intensity. This finding is in accordance with the absorption measurements.