Patent ID: 7538891

Claim:
A method for optically characterizing a surface, comprising: providing a first optical grating and a second optical grating on a sample surface of a sample, the first and second optical gratings being along a first grating direction and a second, different direction within the sample surface and spatially overlapping with each other; directing a plurality of different optical probe beams to the sample surface at different incident directions, respectively; using at least one optical shearing interferometer to receive diffracted light of the different optical probe beams from the first and the second optical gratings, without interaction between two of the different optical probe beams, to obtain phase-shifted optical shearing interferograms along two different shearing directions at each location that are perpendicular to a normal direction of the sample surface at the location; and processing obtained phase-shifted optical shearing interferograms from the different optical probe beams to generate a map of field gradients for both in-plane and out-of-plane displacements on the sample surface.