Importance

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Abstract

It is an object of the invention to provide a synthetic silica glass for a cladding of a core from a fiber laser. The refractive index should be low and there should be no foaming foreign substances. This object is achieved by a synthetic silica glass for an optical element, which contains paramagnetic E′ defect centers in an amount that is sufficient to set the absorption coefficient at 215 nm is in the range between 0.001 cm⁻¹ and 2 cm⁻¹; it contains paramagnetic oxygen defect centers in an amount that is sufficient to set the absorption coefficient at 250 nm is in the range between 0.001 cm⁻¹ and 2 cm⁻¹; the OH group concentration is 5 wtppm or less; the viscosity at 1100° C. is in the range between 1×10^13.5 poise and 1×10^15.5; the total content of metallic elements of Group 3 and Group 13 of the periodic table is 50.000 wtppm or less; and the relative refractive index difference of said synthetic silica glass is in the range between +0.03 % to +3 %, in relation to a synthetic fused silica glass with the absorption coefficient at 215 nm being less than 0.001 cm⁻¹, the absorption coefficient at 250 nm being less than 0.001 cm⁻¹, and the total concentration of the metallic elements contained being 1 wtppm or less, in the wavelength range of 600 nm or more and 1700 nm or less.

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First Claim