Wavelength dependence of the orientation of optic axes in KGW

International audience; We report on the wavelength dependence of the orientation of the optic axes in monoclinic crystals using undoped and neodymium-doped KGd(WO4)2 (KGW) samples. Measurements have been performed over a wide wavelength range from 420 up to 1,580 nm with more than 70 measurement points. This provides the widest measurement range of the optic axis variation ever reported in literature for KGW crystals. With such a measurement, which can be performed in principle in all biaxial crystals, the refractive indices values can be checked with a precision down to 10−3.