| 摘要 |
PROBLEM TO BE SOLVED: To substantially avoid irregular illumination caused by the fact that two beams overlap and interfere with each other on the plane of incidence or irradiated plane of a fly-eye lens. SOLUTION: An illuminating optical system is equipped with a light source 1 that supplies coherent light flux, a light flux splitting means 20 that splits a light flux emitted from the light source 1 into light fluxes, an optical integrator 25 which forms a large number of light source images resting on the light fluxes, and a condenser optical system 26, which illuminates an illumination plane with the condensed light fluxes. The light flux splitting means 20 gives an optical path length difference which is larger than a temporal interference distance prescribed resting on the wavelength distribution of the light fluxes in cross section at a local position to light fluxes that are incident on the optical integrator 25.
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