Patent ID: 7800734

Claim:
An illumination apparatus for illuminating a surface to be irradiated with illumination light emitted from a light source, the illumination apparatus comprising: a reflection type fly-eye optical system, between the light source and the surface to be irradiated, the fly-eye optical system having a plurality of reflection partial optical systems for wavefront-dividing a light beam from the light source and superposing divided portions of the light beam onto each other on the surface to be irradiated; and a reflection type optical system, between the light source and the reflection type fly-eye optical system, for guiding the illumination light to the reflection type fly-eye optical system, wherein the reflection type optical system has a reflecting surface, at least partly constructed by a diffusing surface, the diffusing surface guiding an incident light beam to the reflection type fly-eye optical system, and wherein a diffusion angle of the diffusing surface is such an angle that a full width at half maximum of a range in which a light beam diffused from a point on the diffusing surface by the diffusing surface reaches an entrance surface of the reflection type fly-eye optical system is D/2 to D/100, where D is the entrance diameter of the fly-eye optical system.