Patent ID: 8325323

Claim:
A method, comprising: a) determining at least one of a location-dependent and a time dependent light intensity distribution in an optical element of an optical system; b) determining at least one of a location-dependent and a time-dependent absorbed energy in the optical element; c) determining at least one deformation and change of optical properties of the optical element caused by the absorbed energy; and d) selecting one or several compensation measures, depending on the results of a) through c), wherein the at least one of a location-dependent and a time dependent light intensity distribution is determined by a calculation based on a diffraction angle- and location-dependent light intensity distribution, wherein the diffraction angle- and location-dependent light intensity distribution is determined based on a measurement of light intensity in at least one plane of the optical system transverse to an optical axis of the optical system, and wherein the at least one plane is located between a pupil plane and a field plane of the optical system.