Patent ID: 8810740

Claim:
An illumination optical system comprising: a two-dimensional laser-array light source including a plurality of laser light sources arranged in a two-dimensional array on a plane; an integrator optical system configured to superpose incident light and emit the light to an irradiated surface: a plurality of first lenses disposed parallel to the plane and configured to superpose beams from the two-dimensional laser-array light source in a first axis direction and emit the beams to the integrator optical system while limiting a divergence angle in the first axis direction of the two dimensional array; and a plurality of second lenses disposed rearward of the first lenses and configured to superpose the beams from the two-dimensional laser-array light source in a second axis direction orthogonal to the first axis direction and emit the beams to the integrator optical system while limiting a divergence angle in the second axis direction, wherein, for the beams emitted from the second lenses in both the first axis direction and the second axis direction, the product of the length of an emission area and a divergence angle is equal to the product of the length of an irradiated area on the irradiated surface and an acceptance angle multiplied by a value within, a range of 0.5 to 1.5, inclusive.