The present invention relates to a silica glass substrate including: a first main surface and a second main surface that are facing each other, in which the silica glass substrate has a density of 2.0 g/cm3 or less, the silica glass substrate includes a plurality of bubbles, the silica glass substrate has an average diameter of first recessed portions of 30 m or less, the first recessed portions being formed by the bubbles exposed on the first main surface, and the silica glass substrate has the number of the first recessed portions of 200/mm2 or less on the first main surface.

A quartz glass fibre includes a fibre core of quartz glass produced by modified chemical vapor deposition (MCVD). A fluorine-doped radial layer is provided on the fibre core. A cladding layer of quartz glass contains chlorine and covers the fluorine-doped radial layer to define a hydrogen barrier around the fibre core in response to being irradiated by defect-generating ultra-violet (UV) radiation. The cladding layer has at least one of a combination of E defects and non-bridging oxygen hole center (NBOHC) defects and a combination of SiOH and SiH compounds.

A method of manufacturing a quartz glass fibre includes producing a quartz glass primary preform by modified chemical vapor deposition (MCVD) in a quartz glass substrate tube and inserting the quartz glass primary preform into a glass jacketing tube. Defect-generating UV radiation is irradiated into the cross-sectional area of the glass jacketing tube while combining the quartz glass primary preform with the glass jacketing tube in the jacketing process to form a cladding layer to a secondary preform. A quartz glass fibre is pulled from the secondary preform.

An optical fiber containing an alkali metal and capable of reducing Rayleigh scattering loss is provided. An optical fiber has a core and a cladding made of silica glass and enclosing the core. The cladding contains fluorine and has a refractive index lower than the refractive index of the core. The core contains first group dopants selected from the group of Na element, K element, or a compound thereof at an average concentration of 0.2 ppm or more and 10 ppm or less. The core also contains second group dopants for reducing the viscosity of silica glass and having a diffusion coefficient of 110.sup.12 cm.sup.2/s or more and smaller than the diffusion coefficient of the first group dopants, by an average concentration of 0.2 ppm or more at a temperature of 2000 C. to 2300 C.

A method for producing a silica glass blank co-doped with titanium and fluorine for use in EUV lithography includes (a) producing a TiO.sub.2SiO.sub.2 soot body by flame hydrolysis of silicon- and titanium-containing precursor substances, (b) fluorinating the TiO.sub.2SiO.sub.2 soot body to form a fluorine-doped TiO.sub.2SiO.sub.2 soot body, (c) treating the fluorine-doped TiO.sub.2SiO.sub.2 soot body in a water vapor-containing atmosphere to form a conditioned soot body, and (d) vitrifying the conditioned soot body to form the blank. The blank has an internal transmission of at least 60% in the wavelength range of 400 to 700 nm at a sample thickness of 10 mm, a mean OH content in the range of 10 to 100 wt. ppm and a mean fluorine content in the range of 2,500 to 10,000 wt. ppm. Titanium is present in the blank in the oxidation forms Ti3.sup.+ and Ti.sup.4+.

A process for producing a glass body, the process including flowing oxygen gas from a burner in a furnace at a flow rate of greater than 12.0 standard liters per minute and flowing a precursor gas mixture from the burner. The process further including oxidizing the precursor gas mixture with the oxygen gas to form glass particles and depositing the glass particles on a collection cup to form the glass body.