One aspect relates to a method for producing an optical blank from synthetic quartz glass by vitrifying and shaping a porous, cylindrical SiO.sub.2 soot body having a longitudinal axis, in a heating zone including a melt mold with bottom plate. The SiO.sub.2 soot body vitrified in the heating zone at a vitrification temperature so as to form a fully cylindrical, completely vitrified, transparent quartz glass body. Subsequently, the vitrified quartz glass body is shaped by softening in the melt mold at a softening temperature so as to form a viscous quartz glass mass which partly fills the volume of the melt mold, and cooling the quartz glass mass and removal from the melt mold so as to form the optical blank. During shaping in the melt mold, the fully cylindrical quartz glass body is brought into contact by way of controlled supply with a centering means of the bottom plate.

An optical component made of synthetic quartz glass includes a glass structure substantially free of oxygen defect sites and having a hydrogen content of 0.110.sup.16 to 1.010.sup.18 molecules/cm.sup.3, an SiH group content of less than 210.sup.17 molecules/cm.sup.3, a hydroxyl group content of 0.1 to 100 wt. ppm, and an Active temperature of less than 1070 C. The optical component undergoes a laser-induced change in the refractive index in response to irradiation by a radiation with a wavelength of 193 nm using 510.sup.9 pulses with a pulse width of 125 ns and a respective energy density of 500 J/cm.sup.2 at a pulse repetition frequency of 2000 Hz. The change totals a first measured value M.sub.193 nm when measured using the applied wavelength of 193 nm and a second measured value M.sub.633 nm when measured using a measured wavelength of 633 nm. The ratio M.sub.193 nm/M.sub.633 nm is less than 1.7.

Provided is a method for producing a glass preform for optical fiber which suppresses occurrences of cracks, coloring and foaming in a surface layer when sintering a glass fine particle deposit to allow a production yield to be improved. A method for producing a glass preform for optical fiber comprising the steps of: spraying glass fine particles containing silicon dioxide and germanium dioxide to a starting material moving upward while rotating to produce a glass fine particle deposit; and sintering the glass fine particle deposit while relatively varying a positional relationship between a heating source and the glass fine particle deposit in a sintering apparatus to produce a transparent glass preform, wherein a germanium dioxide reducing gas is contained in an atmosphere gas in the sintering apparatus.

One aspect relates to a method for the manufacture of doped quartz glass. Moreover, one aspect relates to quartz glass obtainable according to the method including providing a soot body, treating the soot body with a gas, heating an intermediate product and vitrifying an intermediate product.

A device for manufacturing SiO.sub.2TiO.sub.2 based glass by growing a glass ingot upon a target by a direct method. The device includes the target, comprising a thermal storage portion that accumulates heat by being preheated, and a heat insulating portion that suppresses conduction of heat from the thermal storage portion in a direction opposite to the glass ingot.

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.

Annealing treatments for modified titania-silica glasses and the glasses produced by the annealing treatments. The annealing treatments include an isothermal hold that facilitates equalization of non-uniformities in fictive temperature caused by non-uniformities in modifier concentration in the glasses. The annealing treatments may also include heating the glass to a higher temperature following the isothermal hold and holding the glass at that temperature for several hours. Glasses produced by the annealing treatments exhibit high spatial uniformity of CTE, CTE slope, and fictive temperature, including in the presence of a spatially non-uniform concentration of modifier.

Hollow ingots of transparent synthetic vitreous silica glass of external diameter greater than 400 mm and internal diameter greater than 300 mm are disclosed. The ingots are substantially free from bubbles or inclusions greater than 100 m in diameter, have no more than 100 ppB of any individual metallic impurity, and have chlorine concentration less than 5 ppM. Also disclosed are methods for producing such ingots, in which a porous soot body of density greater than 0.4 g/cm.sup.3 is deposited on an oxidation resistant mandrel. The soot body is dehydrated on a mandrel comprising graphite, carbon fiber reinforced carbon, silicon carbide, silicon impregnated silicon carbide, silicon carbide-coated graphite or vitreous silica, either under vacuum or in the presence of a reducing gas, and then sintered to transparent pore-free glass under vacuum or in an atmosphere of helium.

Bromine doping of silica glass is demonstrated. Bromine doping can be achieved with SiBr.sub.4 as a precursor. Bromine doping can occur during heating, consolidation or sintering of a porous silica glass body. Doping concentrations of bromine increase with increasing pressure of the doping precursor and can be modeled with a power law equation in which doping concentration is proportional to the square root of the pressure of the doping precursor. Bromine is an updopant in silica and the relative refractive index of silica increases approximately linearly with doping concentration. Bromine can be used as a dopant for optical fibers and can be incorporated in the core and/or cladding regions. Core doping concentrations of bromine are sufficient to permit use of undoped silica as an inner cladding material in fibers having a trench in the refractive index profile. Co-doping of silica glass with bromine and chlorine is also demonstrated.

A method for producing a tubular quartz glass composite body in an outside deposition method comprising the following method steps: providing a substrate tube, rotating the substrate tube about a rotation axis, depositing SiO.sub.2 particles on the outer lateral surface of the substrate tube to form a composite consisting of the substrate tube and an SiO.sub.2 soot body, and sintering the composite by heating at a sintering temperature to form the tubular quartz glass composite body. A substrate tube is provided which consists at least partially of quartz glass of a first quartz glass quality, and that the soot body consist of quartz glass of a second quartz glass quality, wherein the first quartz glass quality has a material-specific viscosity at the sintering temperature that is higher than the material-specific viscosity of the second quartz glass quality.