| 摘要 |
Ultraviolet radiation having a wavelength which is greatly absorbed by oxygen is emitted for a predetermined time from a light source (12) into a housing containing a light transmitting system (BMU), an illuminating optical system (14), and a projection optical system (PL). The gas in the housing is replaced with dry air containing oxygen sufficiently. The energy of the ultraviolet radiation is absorbed by the oxygen in the gas, and ozone is produced by a photochemical reaction. Therefore the contaminant substances adhering to the surface of an optical device are removed by the oxidation by the ozone, and thus the optical device is efficiently cleaned. In such a way an optical device is sufficiently cleaned in a shorter time than in conventional methods, and the illuminating time with ultraviolet radiation is shortened, thereby reducing the damage to the glass material. |
