US Patent 7742160 Determining angle of incidence with respect to workpiece

A method, system and computer program product for determining an angle of incidence of a light beam illuminating a workpiece positioned on a stage are disclosed. A method for determining an angle of incidence of a light beam illuminating a workpiece positioned on a stage may include: positioning a calibration target on the stage with multiple different tilts; first determining an angle of incident of the light beam with respect to the calibration target with each tilt using a detector; mapping a response of the detector to a determined angle of incidence; and second determining the angle of incidence with respect to the workpiece based on a result of the mapping.