One aspect relates to a process for the preparation of a quartz glass body, including providing a silicon dioxide granulate, wherein the silicon dioxide granulate was made from pyrogenic silicon dioxide powder and the silicon dioxide granulate has a BET surface area in a range from 20 to 40 m.sup.2/g, making a glass melt out of silicon dioxide granulate in an oven and making a quartz glass body out of at least part of the glass melt. The oven has at least a first and a further chamber connected to one another via a passage. The temperature in the first chamber is lower than the temperature in the further chambers. On aspect relates to a quartz glass body which is obtainable by this process. One aspect relates to a light guide, an illuminant and a formed body, which are each obtainable by further processing of the quartz glass body.

The present invention relates to a silica glass including bublles in the number of 1×10.sup.7/cm.sup.3 to 1×10.sup.15/cm.sup.3 and having a density of 0.5 g/cm.sup.3 to 1.95 g/cm.sup.3. The present invention also relates to a method for producing a silica glass, including: a step of depositing SiO.sub.2 fine particles generated by flame hydrolysis of a silicon compound, to obtain a silica glass porous body; a step of heating and sintering the silica glass porous body in an inert gas atmosphere, to obtain a silica glass dense body; and a step of performing a foaming treatment to heat the silica glass dense body under a reduced pressure condition.

Provided is a silica glass member which exhibits high optical transparency to vacuum ultraviolet light and has a low thermal expansion coefficient of 4.0−10.sup.−7/K or less at near room temperature, particularly a silica glass member which is suitable as a photomask substrate to be used in a double patterning exposure process using an ArF excimer laser (193 nm) as a light source. The silica glass member is used in a photolithography process using a vacuum ultraviolet light source, in which the fluorine concentration is 1 wt % or more and 5 wt % or less, and the thermal expansion coefficient at from 20° C. to 50° C. is 4.0×10.sup.−7/K or less.

A method for manufacturing an SiO.sub.2—TiO.sub.2 based glass upon a target by a direct method, includes a first process of preheating the target and a second process of growing an SiO.sub.2—TiO.sub.2 based glass ingot to a predetermined length upon the target which has been preheated, wherein the target is heated in the first process such that, in the second process, the temperature of growing surface of the glass ingot is maintained at or above a predetermined lower limit temperature.

A method of forming an optical fiber, including: exposing a soot core preform to a dopant gas at a pressure of from 1.5 atm to 40 atm, the soot core preform comprising silica, the dopant gas comprising a first halogen doping precursor and a second halogen doping precursor, the first halogen doping precursor doping the soot core preform with a first halogen dopant and the second halogen precursor doping the soot core preform with a second halogen dopant; and sintering the soot core preform to form a halogen-doped closed-pore body, the halogen-doped closed-pore body having a combined concentration of the first halogen dopant and the second halogen dopant of at least 2.0 wt %.

A photodarkening-resistant ytterbium-doped quartz optical fiber and a method for prpearing such a fiber are provided. Glass of a photodarkening-resistant ytterbium-doped quartz optical fiber core rod includes at least Yb.sub.2O.sub.3, Al.sub.2O.sub.3, P.sub.2O.sub.5, SiO.sub.2. The proportions of Yb.sub.2O.sub.3, Al.sub.2O.sub.3, and P.sub.2O.sub.5 in the entire substance are Yb.sub.2O.sub.3: 0.05-0.3 mol %, Al.sub.2O.sub.3: 1-3 mol %, and P.sub.2O.sub.5: 1-5 mol %, respectively. In the preparation method for the photodarkening-resistant ytterbium-doped quartz optical fiber, a sol-gel method and an improved chemical vapor deposition method are combined. By using the molecular-level doping uniformity and the low preparation loss thereof respectively, ytterbium ions, aluminum ions and phosphorus ions are effectively doped in a quartz matrix, thereby effectively solving the problems in the optical fiber of high loss, photodarkening caused by cluster or the like, and a central refractive index dip.

A photodarkening-resistant ytterbium-doped quartz optical fiber and a method for preparing such a fiber are provided. Glass of a photodarkening-resistant ytterbium-doped quartz optical fiber core rod includes at least Yb.sub.2O.sub.3, Al.sub.2O.sub.3, P.sub.2O.sub.5, SiO.sub.2. The proportions of Yb.sub.2O.sub.3, Al.sub.2O.sub.3, and P.sub.2O.sub.5 in the entire substance are Yb.sub.2O.sub.3: 0.05-0.3 mol %, Al.sub.2O.sub.3: 1-3 mol %, and P.sub.2O.sub.5: 1-5 mol %, respectively. In the preparation method for the photodarkening-resistant ytterbium-doped quartz optical fiber, a sol-gel method and an improved chemical vapor deposition method are combined. By using the molecular-level doping uniformity and the low preparation loss thereof respectively, ytterbium ions, aluminum ions and phosphorus ions are effectively doped in a quartz matrix, thereby effectively solving the problems in the optical fiber of high loss, photodarkening caused by cluster or the like, and a central refractive index dip.

One aspect relates to a process for the preparation of a quartz glass body, including providing a silicon dioxide granulate, wherein the silicon dioxide granulate was made from pyrogenic silicon dioxide powder and the silicon dioxide granulate has a BET surface area in a range from 20 to 40 m.sup.2/g, making a glass melt out of silicon dioxide granulate in an oven and making a quartz glass body out of at least part of the glass melt. The oven has at least a first and a further chamber connected to one another via a passage. The temperature in the first chamber is lower than the temperature in the further chambers. On aspect relates to a quartz glass body which is obtainable by this process. One aspect relates to a light guide, an illuminant and a formed body, which are each obtainable by further processing of the quartz glass body.

A silica glass for a radio-frequency device has an OH group concentration being less than or equal to 300 wtppm; an FQ value being higher than or equal to 90,000 GHz at a frequency of higher than or equal to 25 GHz and lower than or equal to 30 GHz; and a slope being greater than or equal to 1,000 in a case where the FQ value is approximated as a linear function of the frequency in a frequency band of higher than or equal to 20 GHz and lower than or equal to 100 GHz.

The present invention pertains to: a method for manufacturing an ultraviolet-resistant quartz glass, said method including melting a synthetic silica powder; and a method for manufacturing an ultraviolet-resistant quartz glass, said method including performing arc plasma melting of a silica powder. Provided is an ultraviolet-resistant quartz glass having an ultraviolet-resistance of 2500 seconds, wherein, taking the initial transmittance during irradiation of a quadruple higher harmonic (266 nm) of a YAG laser (irradiation performed at a YAG laser output of 180 mW, pulse width of 20 nsec, and frequency of 80 kHz) at an optical path length of 30 mm to be 100%, the irradiation period until the transmittance falls to 3% is defined as resistance to ultraviolet rays (referred to as ultraviolet-resistance). Also provided is an optical member for YAG-laser higher harmonics, said optical member comprising this quartz glass.