Imaging ellipsometry mapping of photo-induced refractive index in As2S3 films

Photoinduced diffraction grating formation in amorphous As2S3 thin films has been studied using imaging ellipsometry. We first have applied the ACCURION Nanofilm-EP3SE Imaging Spectroscopic Ellipsometer to obtain mapping of diffraction gratings in amorphous As2S3 thin films based on different photoinduced phenomena, namely photodarkening and photoinduced changes of refractive index. The profile and absolute value of refractive index in gratings were studied as a function of exposure. It is shown that underexposure led to the formation of a sinusoidal profile of the refractive index. The proper exposure produced results close to the cycloidal profile. Overexposure led to the same cycloidal profile but with reduced amplitude of refractive index variation in comparison with that obtained under proper exposure.