Patent ID: 6512588
Filing Date: 2003-01-28
Classification: G01B,G03F

Abstract:
A method for correcting an angle &thgr;l indicative of a relative angular orientation of a measurement object for the effects of dispersion caused by gas along a measurement path contacting the measurement object, wherein the angle &thgr;l is measured interferometrically at a wavelength &lgr;l, the method comprising:interferometrically measuring the angular orientation at a first wavelength &lgr;q to give a first angle &thgr;q indicative of the angular orientation; interferometrically measuring the angular orientation at a second wavelength &lgr;u not equal to the first wavelength &lgr;q to give a second angle &thgr;u indicative of the angular orientation; correcting the angle &thgr;l by an additive factor &Dgr;&thgr;l,=âˆ’&boxdr;(&thgr;qâˆ’&thgr;u), where &boxdr;=(nlâˆ’1)/(nqâˆ’nu) is the reciprocal dispersive power of the gas and nl, nq, and nu are the indices of refraction of the gas at wavelengths &lgr;l, &lgr;q, and &lgr;u, respectively.