Narrow-band excimer laser apparatus

摘要: An excimer laser apparatus using a bandwidth-narrowing optical system including beam diameter-enlarging optical and Littrow mounting reflection type diffraction grating is made suitable for use as a laser light source semiconductor lithography or the like by surmounting the limit to bandwidth narrowing due to wavefront distortion induced reflection type diffraction grating. In an having a bandwidth-narrowing optical Littrow mounting type a combination of diameter-enlarging system and slit placed on entrance side grating, diffracted distortion (a measured value He-Ne light) within laser irradiation area diffraction grating in not more than λ/10, where λ is measuring wavelength.