<title>Measurements of index of refraction in the deep and vacuum ultraviolet using the minimum-deviation method</title>

We discuss a procedure for making accurate measurement of the index of refraction, its dispersion, and its temperature dependence, in the deep ultraviolet (near 193 nm), using precision goniometric spectrometers and the minimum deviation method. Measurements of the indices of fused silica and calcium fluoride near 193 nm, with a fractional accuracy of 7 ppm, are discussed. These measurements revealed differences in the indices between different grades of fused silica. Accurate values of the temperature dependencies were determined from measurements of the indices at several temperatures in a 20 degree Celsius range about 20 degrees Celsius. A procedure to measure the index of calcium fluoride in the vacuum ultraviolet region (157 nm) using a N₂ purge housing is discussed.