This technology produces a silica glass material with a promising negative refractive index. The material changes volume via irradiation under UV light, and results in a refractive index capability of 10-2. This makes it applicable to a wide range of fields, including holograms, optical memory, digital recording, and others. The glass has a composition of GeO2— SiO2, and has a content of 0.5 to 90 mol% of GeO2. The resulting form is a thin film that is produced via the high-frequency sputtering method in an argon atmosphere or argon-oxygen mixed atmosphere with an oxygen content of a maximum of 20 vol%.
GeO2—SiO2 glass is especially useful since it is high in transparency in the visible light range and excellent in chemical durability and mechanical durability. When the GeO2 content is too low, the glass cannot secure a large volume change when irradiated with light. On the other hand, when it is too high, the glass is sometimes colored yellow or lowered in water resistance.
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