The present invention features a liquid, solvent-free, silica precursor and two-photon 3D printing process to meet the increasing needs of high-precision glass micro-optics and address the major limitations of current three-dimensional (3D) printing optics. The printed optical elements may be fully converted to transparent inorganic glass at temperatures as low as 600? C. with shrinkages as low as 17%. The present invention includes a complete process chain, from material development, printing process, and performance evaluation of the printed glass micro-optics. 3D printing of glass micro-optics with isotropic shrinkage, micrometer resolution, low deviation peak-to-valley value (<100 nm), and low surface roughness (<6 nm) has been demonstrated. The present invention enables the rapid fabrication of complex glass micro-optics previously impossible using conventional glass optics fabrication processes.

In a known composite material with a fused silica matrix there are regions of silicon-containing phase embedded. In order to provide a composite material which is suitable for producing components for use in high-temperature processes for heat treatment even when exacting requirements are imposed on impermeability to gas and on purity, it is proposed in accordance with the invention that the composite material be impervious to gas, have a closed porosity of less than 0.5% and a specific density of at least 2.19 g/cm.sup.3, and at a temperature of 1000 C. have a spectral emissivity of at least 0.7 for wavelengths between 2 and 8 m.

A synthetic quartz glass lid for use in optical device packages is prepared by furnishing a synthetic quartz glass lid precursor comprising a synthetic quartz glass substrate (1) and a metal or metal compound film (2), and forming a metal base adhesive layer (3) on the metal or metal compound film (2). The metal or metal compound film contains Ag, Bi, and at least one element selected from P, Sb, Sn and In.

A method for producing synthetic quartz glass by fusion of SiO.sub.2 granulate involves synthesizing amorphous SiO.sub.2 primary particles, granulating the amorphous SiO.sub.2 primary particles to form an open-pore SiO.sub.2 granulate, sintering the open-pore SiO.sub.2 granulate by heating in a sintering atmosphere at a sintering temperature and for a sintering period to form a densified SiO.sub.2 granulate, and melting the densified SiO.sub.2 granulate at a melting temperature to form the synthetic quartz glass. To provide an inexpensive production of low-bubble transparent components of quartz glass despite the use of still open-pore SiO.sub.2 granulate, the sintering atmosphere, sintering temperature and sintering duration are adjusted such that the densified SiO.sub.2 granulate still comprises open pores but manifests a material-specific infrared transmission T.sub.1700 at a wavelength of 1700 nm. This transmission is in the range of 50-95% of the infrared transmission T.sub.1700 of quartz glass granules of the same material.

Processes for fusing opaque fused quartz to clear fused quartz to form ultraviolet light transmission windows comprise surrounding a clear fused quartz ingot with an opaque fused quartz sleeve or opaque fused quartz particles, then heating the clear and opaque fused quartz together in a furnace, past the transition temperature of the opaque fused quartz, in order to join the two types of quartz together around the perimeter of the clear fused quartz ingot, but without substantial mixing beyond the interface.

In one method for producing opaque quartz glass, a green body is produced from a slip containing fine, amorphous SiO.sub.2 particles and coarse SiO.sub.2 reinforcement bodies and the green body is sintered by way of a sintering treatment into a blank made from the opaque quartz glass. The reinforcement bodies with a specific density D.sub.K1 are here embedded in a SiO.sub.2 matrix with a specific glass density D.sub.M. Starting from this, in order to provide a blank of opaque quartz glass that is less susceptible to cracking and illustrates homogeneous transmission even in the case of small wall thicknesses, in one aspect sinterable reinforcement bodies are used, the specific density D.sub.K0 of which prior to the sintering treatment is lower than the specific glass density D.sub.M, and which due to the sintering treatment reach the specific density D.sub.K1 which differs from the specific glass density D.sub.M by less than 10%.

To provide opaque quartz glass having no water absorbing properties and being excellent in infrared light shielding properties, and a method for its production. In the production of opaque quartz glass of the present invention, a fine amorphous silica powder and a pore forming agent are mixed, then molded and heated at a predetermined temperature, to obtain opaque quartz glass wherein contained pores are closed pores, the average pore size of pores is from 5 to 20 m, and the content density of pores is high, whereby the heat shielding properties are high.

A method of making a self-supporting inorganic sheet, including: electrostatically depositing a dry inorganic powder on a surface to form an inorganic layer on the surface; and sintering the resulting inorganic layer to form a self-supporting sintered inorganic sheet. The method can additionally include, for example, separating of the self-supporting sintered inorganic sheet from the surface, optionally contacting the separated sintered inorganic sheet with a coupling agent, infiltrating the separated sintered inorganic sheet with a polymer with or without contacting with a coupling agent, or a combination thereof. Also disclosed is a sheet article made by the method.

A method for forming an optical quality glass is provided. The method includes contacting silica soot particles with a basic additive, forming a silica soot compact, and removing the basic additive from the silica soot compact. A method of forming a cladding portion of an optical fiber preform is also provided.

In a known composite material with a fused silica matrix there are regions of silicon-containing phase embedded. In order to provide a composite material which is suitable for producing components for use in high-temperature processes for heat treatment even when exacting requirements are imposed on impermeability to gas and on purity, it is proposed in accordance with the invention that the composite material be impervious to gas, have a closed porosity of less than 0.5% and a specific density of at least 2.19 g/cm.sup.3, and at a temperature of 1000 C. have a spectral emissivity of at least 0.7 for wavelengths between 2 and 8 m.