On the effective wavelength in two-wavelength interferometry

Abstract

A discussion on the effective wavelength in two-wavelength interferometry is given. A definition, different from the commonly adopted one, is presented and its validity is discussed. By adopting this new effective wavelength the range over which lengths can be measured using interferometric techniques can be vastly increased, without introducing phase unwrapping ambiguities within this increased range. A graph is presented from which a method is derived, enabling an efficient use of this new effective wavelength.