Double phase modulation in the hybrid spatial-chromatic domain as a refractometry tool

Double phase modulation in spatial and chromatic coordinates allows real-time analysis of refractive indexes. The experimental set-up consists of a two-beam interferometer associated to a spectroscopic device illuminated by a white light source. Relative phase stores (in real time) the differential refractive index in its second (crossed) derivative with respect to the chromatic and spatial coordinates. Double modulation applies both to dispersive and non-dispersive media; two different methods for data processing are proposed accordingly. Maximum precision is attained when non-dispersive samples are handled. The method itself suggests the appropriate technique for data processing. Experimental evidence is provided. (C) 2000 Elsevier Science B.V. All rights reserved.