Patent ID: 7403290

Claim:
Method for determining the shape of a rough surface of an object having a given roughness related height variation comprising the steps of: providing an interferometer for wave front measurement comprising a measurement beam of electromagnetic radiation having a wavelength λ not exceeding ten times of said given roughness related height variation of said object surface, which measurement beam comprises an incoming wave for illuminating said object surface and an outgoing wave comprising radiation from said incoming wave reflected off said object surface, directing said incoming wave of said measurement beam onto said object surface at least two different probing locations, thereby illuminating an areal element of said object surface at each of said probing locations, wherein said areal element is dimensioned such that the maximum height variation of said object surface within the respective illuminated areal element is smaller than said given roughness related height variation, and measuring the respective phase distribution of said outgoing wave by means of said interferometer at each probing location.