Patent ID: 7440206

Claim:
An optical properties restoration apparatus for improving the reliability and longevity of optical properties of an optical system by preventing, suppressing, or improving degradation of optical properties of the optical system, wherein said optical system lies upon a vacuum boundary and is provided within a near vacuum zone where organic components may be decomposed, said degradation is caused by carbon deposited or accumulated upon light irradiation surfaces, light reflection surfaces, light emission surfaces (collectively called ‘lighting surfaces’) of said optical system, and said light emission surfaces facing said vacuum zone, said optical properties restoration apparatus comprising: a means to create said near vacuum zone to excite an oxidation reaction of carbon, said near vacuum zone facing said lighting surfaces of said optical system that lies upon the vacuum boundary; a means to generate a flow of an oxygen atom-containing gas such as water gas or oxide gas in said near vacuum zone; and a means to supply active energy in said near vacuum zone to cause a single oxidation reaction consisting of a carbon oxidation reaction between said oxygen atom-containing gas and the carbon, wherein a lower limit value for a partial pressure of said gases containing oxygen atoms that is supplied to said near vacuum zone is set to a level over a speed of the carbon buildup, and said optical properties restoration apparatus removes or reduces the accumulated carbon, which deposits on said lighting surfaces of the optical system during operation of the optical system, by the carbon oxidation reaction.