PURPOSE: To obtain the device having long life by constituting the lasre device by an SiO2 film in which the concentration of impurities in a substance with a low refractive index is made 50ppm or lower when dielectric multilayer films consisting of a substance with a high refractive index and the substance with the low refractive index are coated alternately on a substrate and the lasre device with two kinds of lasre mirrors having different characteristics is manufactured.

CONSTITUTION: The lasre device is produced in such a manner that the mirror 34 at the high reflection side, the inside thereof has the multilayer film 36, is mounted at one end of a lasre tube 31 into which a mixed gas 32 of He and Ne is enclosed, and the mirror 35 at the output side, the inside thereof has the multilayer film 37 similarly, is attached at the other end. The lasre tube is constituted in this manner, light oscillated in the gas 32 is reflected by the multilayer film 36 approximately complete, the reflected light is reflected by the multilayer film 37 again, the reflection is repeated, and one part of light is passed through an antireflection film 38, and extracted to the outside. In this constitution, the both multilayer films 36 and 37 are prepared by the alternately laminated films of the substances with the high and low refractive indices, particularly, the substance with the low refractive index is formed by the SiO2 film, the concentration of impurities therein is 50ppm or lower.