MICROSCOPIC SINGLE-CRYSTAL REFRACTOMETRY AS A FUNCTION OF WAVELENGTH

The refractive indices of crystal fragments 50-200 mum in size can be measured for light wavelengths between 365 and 1100 nm with a spindle- stage refractometer. Established methods from optical crystallograpy a re used to orient a crystal on the microscope spindle stage and then t o match its refractive index to an immersion fluid. The refractive ind ex of the fluid for the wavelength of light and matching temperature i s determined by comparison of a reference crystal on a second spindle axis with the fluid under the match conditions. Investigations of new nonlinear-optical crystals admirably demonstrate the advantages of mea suring the refractive index to +/-0.0004 in small single crystals.