US Patent 7771065 Optical unit and exposure apparatus having the same

An optical unit including a plate, an optical element, a fixing device for partially fixing the optical element against the plate, and a deforming device, located between the plate and the optical element, for applying a deforming force to the optical element to change a surface shape of the optical element. The deforming device includes poles for contacting a back face of the optical element, and actuators for driving the poles against the plate.