Two-wavelength antireflection film and objective lens coated with two-wavelength antireflection film

摘要

A two-wavelength antireflection film to prevent light in two-wavelength regions of a deep-ultraviolet region and a region from a visible region to the near-infrared region on a surface of a substrate by coating the two-wavelength antireflection film on the surface of the substrate which penetrates light from the deep-ultraviolet region to the near-infrared region, comprising a first thin film which is formed on the substrate, and has a refractive index of 1.6 to 2.0 and optical film thickness of 0.4&lgr; to 0.7&lgr; for design main wavelength (&lgr;), a second thin film which is formed on the first thin film, and has a refractive index of 1.35 to 1.55 and an optical film thickness of 0.05&lgr; to 0.6&lgr; for the design main wavelength &lgr;, a third thin film which is formed on the second thin film, and has a refractive index of 1.6 to 2.0 and an optical film thickness of 0.1&lgr; to 0.5&lgr; for the design main wavelength &lgr;, and a fourth thin film which is formed on the third thin film, and has a refractive index of 1.35 to 1.55 and an optical film thickness of 0.2&lgr; to 0.35&lgr; for the design main wavelength &lgr;.