Patent ID: 7573019
Filing Date: 2009-08-11
Classification: G01J,G03F

Abstract:
1. An illumination optical apparatus for illuminating an illumination target surface with light beam from a light source, comprising a light detecting apparatus, arranged in an illumination path, which detects light which enters along a direction from the light source to the illumination target surface, the light detecting apparatus comprising: a light splitting element including two optical surfaces positioned in the optical path; and a photoelectric detector, wherein the light splitting element further comprises an incident angle conversion section, arranged in the illumination path, which converts a part of light which enters one optical surface out of the two optical surfaces into light entering the other optical surface at an incident angle greater than or equal to a total reflection angle, and wherein the photoelectric detector photo-detects light which propagates inside the light splitting element and is guided from a side face of the light splitting element.