A disclosed multimode optical fiber comprises a core and a cladding surrounding the core. The core has an outer radius r.sub.1 in between 20 μm and 30 μm. The cladding includes a first outer cladding region having an outer radius r.sub.4a and a second outer cladding region having an outer radius r.sub.4b less than or equal to 45 μm. The second outer cladding region comprises silica-based glass doped with titania. The optical fiber further includes a primary coating with an outer radius r.sub.5 less than or equal to 80 μm, and a thickness (r.sub.5−r.sub.4) less than or equal to 30 μm. The optical fiber further includes a secondary coating with an outer radius r.sub.6 less than or equal to 100 μm. The secondary coating has a thickness (r.sub.6−r.sub.5) less than or equal to 30 μm, and a normalized puncture load greater than 3.6×10.sup.−3 g/micron.sup.2.

A continuous sol-gel process for producing silicate-containing glasses and glass ceramics is proposed, comprising the following steps: (a) continuously feeding a silicon tetraalkoxide, a silicon alkoxide with at least one non-alcoholic functional group and an alcohol into a first reactor (R1), and at least partially hydrolyzing by the addition of a mineral acid to obtain a first product stream (A); (b) continuously providing a second product stream (B) in a second reactor (R2) by feeding a metal alkoxide component or continuously mixing an alcohol and a metal alkoxide component; (c) continuously mixing product streams (A) and (B) in a third reactor (R3) for producing a presol to obtain a third product stream (C); (d) continuously adding water or a diluted acid to the product stream (C) to obtain a sol (gelation); (e) continuously filling the emerging sol into molds to obtain an aquagel; (f) drying the aquagels to obtain xerogels; (g) sintering the xerogels to obtain silicate-containing glasses and glass ceramics.

According to embodiments, a method of making a microstructured glass article includes bundling M bare optical fibers in a fiber bundle, wherein M is an integer greater than 100. Thereafter, the fiber bundle may be inserted in a cavity of a soot preform. The soot preform may have a density of less than or equal to 1.5 g/cm.sup.3 and comprise silica-based glass soot. The soot preform and inserted fiber bundle may then be consolidated to form a microstructured glass article preform. The microstructured glass article preform may then be drawn into the microstructured glass article comprising M core elements embedded in a cladding matrix.

A method of forming an optical element is provided. The method includes producing silica-based soot particles using chemical vapor deposition, the silica-based soot particles having an average particle size of between about 0.05 μm and about 0.25 μm. The method also includes forming a soot compact from the silica-based soot particles and doping the soot compact with a halogen in a closed system by contacting the silica-based soot compact with a halogencontaining gas in the closed system at a temperature of less than about 1200° C.

A continuous sol-gel process for producing silicate-containing glasses and glass ceramics is proposed, comprising the following steps: (a) continuously feeding a silicon tetraalkoxide, a silicon alkoxide with at least one non-alcoholic functional group and an alcohol into a first reactor (R1), and at least partially hydrolyzing by the addition of a mineral acid to obtain a first product stream (A); (b) continuously providing a second product stream (B) in a second reactor (R2) by feeding a metal alkoxide component or continuously mixing an alcohol and a metal alkoxide component; (c) continuously mixing product streams (A) and (B) in a third reactor (R3) for producing a presol to obtain a third product stream (C); (d) continuously adding water or a diluted acid to the product stream (C) to obtain a sol (gelation); (e) continuously filling the emerging sol into molds to obtain an aquagel; (f) drying the aquagels to obtain xerogels; (g) sintering the xerogels to obtain silicate-containing glasses and glass ceramics.

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 for producing titanium-doped synthetic quartz glass includes: (A) providing a liquid SiO.sub.2 feedstock material that comprises more than 60% by weight of the polyalkylsiloxane D4; (B) evaporating the liquid SiO.sub.2 feedstock material to produce a gaseous SiO.sub.2 feedstock vapor; (C) evaporating a liquid TiO2 feedstock material to produce a gaseous TiO2 feedstock vapor; (D) converting the SiO.sub.2 feedstock vapor and the TiO2 feedstock vapor into SiO2 particles and TiO2 particles, respectively; (E) depositing the SiO2 particles and the TiO2 particles on a deposition surface while forming a titanium-doped SiO.sub.2 soot body; (F) vitrifying the titanium-doped SiO.sub.2 soot body while forming the synthetic quartz glass, whereby the TiO2 concentration of the synthetic quartz glass is between 5% by weight and 11% by weight. The liquid SiO.sub.2 feedstock material comprises at least one additional component made of the polyalkylsiloxane D3 having a weight fraction of mD3 and one additional component made of the polyalkylsiloxane D5 having a weight fraction of mD5 at a weight ratio of mD3/mD5 in a range of 0.01 to 1, and the liquid SiO.sub.2 feedstock material provided is evaporated while maintaining the weight ratio of mD3/mD5 and at least 99% by weight thereof are evaporated to form the gaseous SiO.sub.2 feedstock vapor.

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.

A method is provided that includes: forming a low-index trench region with a first density; forming an inner barrier layer comprising silica around the trench region at a second density greater than the first density; depositing silica-based soot around the first barrier layer to form an overclad region at a third density less than the second density; inserting a core cane into a trench-overclad structure; forming an outer barrier layer comprising silica in an outer portion of the overclad region at a fourth density greater than the third density; flowing a down dopant-containing gas through the trench-overclad structure to dope the trench region with the down dopant, and wherein the barrier layers mitigate diffusion of the down-dopant into the overclad region; and consolidating the trench-overclad and the core cane.

Methods for selecting titania-doped quartz glass which experiences a reduction in OH group concentration of less than or equal to 100 ppm upon heat treatment at 900° C. for 100 hours as suitable material for the EUV lithography member.