Abstract: A total reflection mirror having a mirror coating formed on one main surface of a transparent substrate includes forming a correction coating with a reflection index approximately equal to that of the transparent substrate on second main surface of the transparent substrate and correcting warping of the transparent substrate due to a stress of the mirror coating, using a stress of the correction coating.

Abstract: A half mirror comprises: a beam splitter coating formed on one main surface of a transparent substrate; an anti-reflection coating formed on the other main surface; and a correction coating having substantially the same refractive index as that of the transparent substrate is formed between the transparent substrate and the anti-reflection coating so that a warpage of the transparent substrate caused by a stress of the beam splitter coating is corrected by a stress of the correction coating.

Abstract: A numerical aperture controlling filter, including: a first region that allows, when a laser beam having a different wavelength is incident on the numerical aperture controlling filter, a transmission of laser beams having all the wavelengths; and a second region that blocks a transmission of a laser beam having a predefined wavelength, wherein: different materials are used for outermost layers of a first optical thin film that is formed in the first region and a second optical thin film that is formed in the second region; and an optical path length of either of the first optical thin film or the second optical thin film is adjusted by means of etching after depositing the first optical thin film and the second optical thin film.