Abstract: A system for facilitating the measurement of optical parameters of a substance sitting on a surface, so that identification of the substance by reflectance spectroscopy can be made without ambiguity; the system comprises a structure using a bistatic arrangement and an accompanying method to limit, to just two beams, the propagation of light from a laser transmitter capable of producing coherent light of multiple wavelengths, via an interposed transparent dielectric, to a receiver thereby preventing multiple reflections within the transparent dielectric from reaching the receiver; and the bistatic arrangement comprises a multi-wavelength laser transmitter and a receiver mounted on a telescoping boom, with both the laser transmitter and receiver being independently orientable, with the positions and orientations of the laser transmitter, the receiver and the telescoping boom electronically sensed at all times.