AN APPARATUS FOR MEASURING A REAL INDEX OF REFRACTION

摘要

An apparatus (10) that can measure a space between a first surface (16) and a second surface (14). The apparatus (10) may include a light source (28) that can reflect a light beam (30) from the first and second surfaces (16, 14). A birefrigent element (50) may split the reflected light beam into an ordinary beam (54) and an extraordinary beam (56). The ordinary and extraordinary beams (54, 56) are detected by a photodetector (60). The apparatus (10) may include a controller (84) that is coupled to the photodetector (60) and which can compute the space (12) from a phase value that is determined from data collected when the mechanism (86) varies the phase between the ordinary and extraordinary beams (54, 56), and a ratio between a first modulation amplitude detected from light reflected from the first and second surfaces (16, 14) and a second modulation amplitude detected from light reflected from the first surface (16) when the second surface (14) is not adjacent to the first surface (16). The ratio can also be used to compute the reflectance and index of refraction of the second surface (14). This method thus allows the space (12) to be computed without performing a separate measurement to determine the index of refraction.