Method and system for correcting image changes

A method, comprising:

• a) determining at least one location-dependent and time dependent intensity distribution in at least one optical element of an optical system;
• b) determining at least one location-dependent and time-dependent absorbed energy in the optical element for which the intensity distribution has been determined;
• 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 steps a) through c),
• wherein step a) by a calculation based on at least one of the diffraction angle- and location-dependent intensity distribution,
• wherein at least one of the diffraction angle- and location-dependent intensity distribution is determined or considered, based on the measurement of the intensity in at least one plane of the optical path, transverse to the optical axis of the optical system, and
• wherein the at least one plane has a paraxial sub aperture ratio in a range selected from the group consisting of −0.25 to +0.25, −0.75 to −1, 0.75 to 1, and/or if the at least one plane includes more than one plan two planes with different prefixes of the paraxial sub aperture ratio and several planes with equidistantly spaced paraxial sub aperture ratios.

An optical system, comprising:

• at least one optical element;
• and
• at least one image detector capable of being located in an optical path of the optical system so that the at least one detector can directly measure a location-resolved and/or time resolved intensity distribution in the optical path,
• wherein the system is a projection lens for microlithography.