Importance

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Abstract

An illumination optical system includes a first diffraction optical element, a second diffraction optical element and a condenser lens. The first diffraction optical element has a plurality of micro diffraction optical elements, which have a first optical power in a first direction and an optical power different from the first optical power in a second direction, perpendicular to the first direction. The second diffraction optical element has a plurality of micro diffraction optical elements, which have a second optical power in the second direction and an optical power different from the second optical power in the first direction. The first optical power is different from the second optical power. Light supplied from a light source forms a plurality of secondary light sources by passing through the first and second diffraction optical elements. Light from the secondary light sources passing through the condenser lens generates Kohler illumination on a surface to be irradiated.

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First Claim