Two-wavelength interferometry combined with N-point technique

Combining two-wavelength interferometry with the N-point technique (also called spatial carrier phase shifting interferometry) allows for the measurement of objects with large step heights that single-wavelength, phase-shifting interferometry can not correctly resolve. This combination yields some significant advantages but entails some limitations as well. Advantages include the elimination of the need for a phase shifter and the fast measurement of large step heights. The major limitations is a decrease in the measurable slope range of the object. Other concerns include setting the correct carrier frequency of the fringes for both wavelengths and coping with the magnification of the inherent phase errors of the N-point technique. The presentation considers real as well as simulated objects.