OPTICAL ANISOTROPY AND BIREFRINGENCE OF CuAlS2 CRYSTALS

Optical spectra were investigated in a spectral range of (300 - 700) nm for CuAlS2 single crystals. Transmission and wavelength modulated transmission spectra demonstrated presence of some impurity absorption bands in the region of optical transparency of crystals. Optical functions (real and imaginary components of the dielectric function, refractive index and extinction coefficient) have been calculated from the optical reflection spectra by means of the Kramers-Kronig relations. A strong anisotropy and birefringence have been revealed for CuAlS2 crystals. Two isotropic points have been found in (100) oriented platelets around 380 nm and 530 nm. The position of the isotropic point around 530 nm was found to be strongly influenced by the technological conditions of crystal growth and platelet thickness, it being situated at 535 nm for a platelet with thickness of 223 µm. An optical band-pass filter was constructed with such a platelet placed between two Gran-Thompson prism crossed polarizers.