Patent ID: 7428685
Filing Date: 2008-09-23
Classification: G01B,G03F

Abstract:
1. A method comprising: providing an interference signal S(t) from two beams directed along different paths, wherein the signal S(t) is indicative of changes in an optical path difference n{tilde over (L)}(t) between the different paths, where n is an average refractive index along the different paths, {tilde over (L)}(t) is a total physical path difference between the different paths, and t is time; providing one or more coefficients representative of one or more errors that cause the signal S(t) to deviate from an ideal expression of the form A calculating a linear combination of values of the signal S(t); and reducing the effect of the deviation of S(t) from the ideal expression on an estimate of {tilde over (L)}(t) using an error signal generated from the coefficients and one or more error basis functions derived at least in part from the linear combination of values of the signal S(t).