OPTICAL ELEMENT AND MANUFACTURING METHOD THEREOF

摘要

The present invention relates to an optical element which comprises a multi-layer antireflective film (optical inorganic thin film) (16) on an optical element substrate (10). A first layer (starting from the closest side to the optical element substrate: the same shall apply hereafter.) of the optical inorganic thin film is a vapor-deposited film (hereinafter called "specified vapor-deposited film") composed of either 1) a mixture or compound of La oxide and Ti oxide, or 2) a mixture or compound of La oxide and Ta oxide and shows a refractive index n D =1.95-2.25. In addition, a final layer is to be a vapor-deposited film comprising SiO 2 , and a middle layer composed of a single or multi-layered vapor-deposited film which comprises one metal oxide selected from a group consisting of ITO (indium tin oxide) and oxides of Group 4 and 5 elements in the fourth to sixth periods is included in the inner side of the final layer. This optical element hardly develops initial swelling while a high degree of heat resistance is maintained.