Abstract: The present invention provides a TiO2—SiO2 glass whose coefficient of linear thermal expansion in the range of the time of irradiation with EUV light is substantially zero when used as an optical member of an exposure tool for EUVL and which has extremely high surface smoothness. The present invention relates to a TiO2-containing silica glass having a TiO2 content of from 7.5 to 12% by mass, a temperature at which a coefficient of linear thermal expansion is 0 ppb/° C., falling within the range of from 40 to 110° C., and a standard deviation (?) of a stress level of striae of 0.03 MPa or lower within an area of 30 mm×30 mm in at least one plane.

Abstract: A method for manufacturing a preform for optical fibers by a vapor deposition process wherein an intermediate step is carried out between one deposition phase and the next deposition phase(s), wherein the intermediate step includes supplying an etching gas to the supply side of the hollow substrate tube.

Abstract: Disclosed are process and apparatus for making high purity fused silica glass materials. The process involves depositing soot particles onto an essentially planar deposition supporting surface and modulation of motion of the soot-generating device relative to the deposition supporting surface to result in a low local soot density variation. The apparatus is designed to implement the planar deposition process. The invention makes it possible to produce fused silica glass without the use of potentially contaminating refractory bricks.

Abstract: A method for producing a fused silica glass containing titania includes synthesizing particles of silica and titania by delivering a mixture of a silica precursor and a titania precursor to a burner, growing a porous preform by successively depositing the particles on a deposition surface while rotating and translating the deposition surface relative to the burner, and consolidating the porous preform into a dense glass.

Abstract: The invention relates to a method for manufacturing a final optical fiber preform by overcladding, said method comprising the steps of providing a primary preform; positioning said primary preform within at least one tube, wherein the at least one tube partly covers the primary preform to create a zone to be overcladded, being an overclad zone, which overclad zone is located on the primary preform outside the at least one tube; injecting a gas into the annular space between the primary preform and the at least one tube under overpressure relative to the pressure outside the at least one tube; overcladding the primary preform in the overclad zone with an overcladding material using an overcladding device. The invention also relates to an apparatus for carrying out the method. The invention allows overcladding a primary preform at low cost while maximally limiting the incorporation of impurities into the silica overclad.

Abstract: A fused silica glass and a fused silica article having a combined concentration of at least one of OH and OD of up to about 50 ppm. The fused silica glass is formed by drying a fused silica soot blank or preform in an inert atmosphere containing a drying agent, followed by removal of residual drying agent from the dried soot blank by heating the dried soot blank in an atmosphere comprising an inert gas and of oxygen.

Abstract: There is provided a manufacturing apparatus of a porous glass base material which can prevent soot from being formed on an upper surface (ceiling) of the process chamber, and reduce the amount of soot that comes off the upper surface and falls. A manufacturing apparatus of a porous glass base material 4 deposits glass particles produced by subjecting a material gas to flame hydrolysis, onto a starting member 1 placed vertically. Here, a plurality of gas inlets 5 are provided in one or more lateral walls of a process chamber including a burner 2 for the deposition therein, in upper portions of the lateral walls and along a ceiling of the process chamber.

Abstract: Microstructured optical fiber and method of making. Glass soot is deposited and then consolidated under conditions which are effective to trap a portion of the consolidation gases in the glass to thereby produce a non-periodic array of voids which may then be used to form a void containing cladding region in an optical fiber. Preferred void producing consolidation gases include nitrogen, argon, CO2, oxygen, chlorine, CF4, CO, SO2 and mixtures thereof.

Abstract: A method of making an optical fiber preform includes depositing silica glass soot on the inside of a substrate tube via a chemical vapor deposition operation. The silica glass soot is consolidated into silica glass under controlled conditions such that the consolidated silica glass on the interior of the substrate tube contains a non-periodic array of gaseous voids in a cladding region of the optical fiber preform. The optical fiber preform may be used to produce an optical fiber having a core and a cladding containing voids formed from the gaseous voids of the cladding region of the optical fiber preform. The core of the optical fiber has a first index of refraction and the cladding has a second index of refraction less than that of the core.

Abstract: An apparatus for measuring the weight of a preform for optical fibers during a chemical deposition process for the formation of a preform is disclosed. The apparatus has at least one elastic constraint associated with at least one end portion of an elongated element made of a chemical deposition substrate for the formation of the preform, a device for inducing an oscillation, for example axial, on said elongated element, a device for detecting the frequency of oscillation of said elongated element, and a device for calculating the weight of the preform according to the detected frequency of oscillation. Advantageously, the device allows the realisation of a method for measuring the weight of the preform wherein the errors in measurement caused by thermal drift effects, by the axial distribution of the masses on the preform and by loads which are different from the mass of the preform in formation are reduced to below the required precision in measurement.

Abstract: Optical fiber preforms can comprise a glass preform structure with an inner cavity. A powder can be placed within the inner cavity having an average primary particle size of less than about one micron. The powder can be in the form of an unagglomerated particles or a powder coating with a degree of agglomeration or hard fusing ranging from none to significant amounts as long as the primary particles are visible in a micrograph. Powders can be placed within a preform structure by forming a slurry with a dispersion of submicron/nanoscale particles within a cavity within the preform. In other embodiments, a powder coating is formed within a preform structure by depositing the powder coating directly from a reaction product stream. The formation of the powder coating can be formed within the reaction chamber or outside of the reaction chamber by flowing the product particle stream through a conduit leading to the preform structure. In additional embodiments, a powder coating is placed on an insert, e.g.

Abstract: The invention relates to an optical fibre comprising a gain medium which is equipped with: a core (22) which is formed from a transparent material and nanoparticles (24) comprising a doping element and at least one element for enhancing the use of said doping element; and an outer cladding (26) which surrounds the core. The invention is characterised in that the doping element is erbium (Er) and in that the enhancing element is selected from among antimony (Sb), bismuth (Bi) and a combination of antimony (Sb) and bismuth (Bi). According to the invention, one such fibre is characterised in that the size of the nanoparticles is variable and is between 1 and 500 nanometres inclusive, and preferably greater than 20 nm.

Abstract: Known methods for producing a semifinished product for an optical component of synthetic quartz glass of high homogeneity require a great number of forming or shaping steps for homogenization, which is troublesome in terms of energy and time and entails the risk that impurities might be introduced.

Abstract: The present invention relates to a device for manufacturing an optical preform by means of an internal vapour deposition process, said device comprising an energy source and a substrate tube, which substrate tube comprises a supply side for supplying glass-forming precursors and a discharge side for discharging constituents that have rot been deposited on the interior of the substrate tube, said energy source being movable along the length of the substrate tube between a point of reversal at the supply side and a point of reversal at the discharge side.

Abstract: A glass powder or a glass-ceramic powder is provided that includes multicomponent glasses with at least three elements, where the glass powder or a glass-ceramic powder has a mean particle size of less than 1 ?m. In some embodiments, the mean particle size is less than 0.1 ?m, while in other embodiments the mean particle size is less than 10 nm.

Abstract: A method is provided for forming an optical fiber amplifier. The method comprises providing a composite preform having a gain material core that includes one or more acoustic velocity varying dopants to provide a longitudinally varying acoustic velocity profile along the gain material core to suppress Stimulated Brillouin Scattering (SBS) effects by raising the SBS threshold and drawing the composite preform to form the optical fiber amplifier.

Abstract: An apparatus for and method of depositing material on a substrate, the method comprising the steps of: delivering from a first outlet a stream of droplets of a precursor liquid towards a substrate; applying an electric field between the first outlet and the substrate; and delivering from a second outlet a flow of fuel about the stream of droplets such as to provide an annular flame combustion region between the first outlet and the substrate through which at least a portion of the stream of droplets passes before reaching the substrate, whereby the precursor liquid is one or both of chemically reacted and decomposed to provide the deposited material.

Abstract: The invention starts from a known method for producing a glass body, comprising forming a cylindrical blank by successive deposition of a plurality of material layers on the outer surface of a substrate body which is rotating about its longitudinal axis, by using an arrangement of a plurality of depositors which are directed onto the substrate body and which are fed via supply lines with process media for material layer deposition and which are moved without a reversing movement relative to the longitudinal axis of the substrate body. Starting therefrom, to provide a method for producing a glass body of high homogeneity that can be realized in a constructionally simple way, the invention suggests that the movement of the depositor arrangement along the longitudinal axis of the substrate body should be accompanied by a displacement of the substrate body.

Abstract: A method for manufacturing a preform having a core and a multilayer clad, includes covering a circumference of a rod including at least the core and an inner clad layer with a first tube including at least a high viscosity clad layer, and unifying the rod and the first tube by heating and contracting the first tube.

Abstract: A cane having optical properties includes: a core formed of a semiconductor material; and a transparent cladding formed of glass, glass-ceramic, or polymer coaxially oriented about the core, the cane may be used to produce a photovoltaic device, including: a semiconductor core including at least one p-n junction, defined by respective n-type and p-type regions; a substantially transparent cladding in coaxial relationship with the semiconductor core, forming a longitudinally oriented cane; and first and second electrodes, each being electrically coupled to a respective one of the n-type and p-type regions.

Abstract: A method and device for vaporizing a liquid reactant. A vaporizing plate having a top surface defines a liquid flow channel, the channel being laterally delimited by edges having a height greater than a minimum thickness of liquid reactant required to generate vapor under film or nucleate boiling regime. A heating system is associated to the vaporizing plate for heating the liquid reactant over a minimum temperature required to generate vapor under nucleate or, preferably, film boiling regime. A cap covers the vaporizing plate to collect the vapor at a predetermined pressure and provided with a vapor exit and a liquid feeder feeds the liquid reactant onto the vaporizing plate.

Abstract: In a known method for the production of a blank mold for optical fibers, a fluorine-doped SiO2 enveloping glass is produced on a core glass cylinder that rotates about its longitudinal axis, wherein a silicon-containing starting substance is fed to a plasma burner, said substance is then oxidized in a plasma flame assigned to the plasma burner to obtain SiO2 particles, the SiO2 particles are deposited by layers on the enveloping surface of the cylinder of the core glass cylinder in the presence of fluorine and sintered into the enveloping glass. The invention aims at providing an economical method, which builds upon the above-mentioned method, in order to produce a blank mold from which optical multi-mode fibers (52) can be obtained.

Abstract: A known method for producing synthetic quartz glass with a predetermined hydroxyl group content comprises the following steps: a porous SiO2 soot body is produced by flame hydrolysis or oxidation of a silicon-containing start compound and by layerwise deposition of SiO2 particles on a rotating support; the soot body is subjected to a dehydration treatment in a reaction gas-containing drying atmosphere at a drying temperature for removing hydroxyl groups; and the SiO2 soot body is vitrified into a body consisting of the synthetic quartz glass. Starting from this, and in order to permit a reproducible and reliable manufacture of synthetic, UV-radiation resistant quartz glass with predetermined hydroxyl group content and low chlorine content, it is suggested according to the invention that the dehydration treatment according to method step (b) comprises a drying phase during which ozone is used as the reaction gas, whereby the ozone content of the drying atmosphere is between 0.5% by vol. and 10% by vol.

Abstract: A method for preparing doped oxide material, in which method substantially all the reactants forming the oxide material are brought to a vaporous reduced form in the gas phase and after this to react with each other in order to form oxide particles. The reactants in vaporous and reduced form are mixed together to a gas flow of reactants, which gas flow is further condensated fast in such a manner that substantially all the component parts of the reactants reach a supersaturated state substantially simultaneously by forming oxide particles in such a manner that there is no time to reach chemical phase balances.

Abstract: A method for feeding a flow of gas to a burner for manufacturing an optical fiber preform. The burner has a plurality of coaxial tubes, each two adjacent coaxial tubes defining an annular channel between themselves; an annular gas distribution chamber at one extremity of the annular channels and in fluid communication therewith, the annular distribution chamber being delimited in the radial direction by an inner and an outer surface. The flow of gas is introduced into the distribution chamber so that the direction of its radially outermost portion is tangential to the radially outer surface of the distribution chamber. The method allows obtaining a better gas velocity distribution in the annular channels.

Abstract: Device and method for chemical deposition on an elongated member of vitreous material in which a rotating gripping member causes a first end portion of the elongated member to rotate. The second end portion of the elongated member is borne by a pair of supporting members which are axially spaced apart (L1) and are capable of permitting angular rotational movement and axial sliding of the second end portion. Each supporting member also applies a radial constraint preventing the second end portion from moving away from the axis of rotation, thus forcing the second portion and the elongated member to lie with a longitudinal axis coaxial with the axis of rotation. Any curvature of the elongated member is corrected and recovered in this way.

Abstract: A fiber stub assembly is provided that has a cladding layer that is reduced in diameter near the end of the stub into which light is launched from a light source. The portion of the stub having the cladding layer with the reduced diameter is surrounded by a light-absorbing material that is in contact with the inner surface of the ferule and with the outer surface of the cladding layer. The light-absorbing material and the outer surface of the cladding layer have indices of refraction that are matched, or very close to one another, such that any modes of light that are propagating in the cladding layer that impinge on the interface propagate into the light-absorbing material and are absorbed thereby. The reduced diameter of the cladding layer and the surrounding light-absorbing material form a pin hole opening through which light is received.

Abstract: A method for manufacturing an optical fiber preform and an optical fiber preform apparatus are provided which can reduce hydroxyl groups in an optical fiber preform to a sufficient level without requiring any special equipment or operating conditions. When an optical fiber preform is manufactured by the vapor-phase deposition method, the dehydrating treatment is performed on a porous core preform that is obtained by depositing glass microparticles. In this treatment, a dehydrating agent is supplied to a dehydration apparatus through a feeding pipe and a main feeding pipe made of a material having a water permeance factor of 1.0×10?11 g·cm/cm2·s·cmHg or less, thereby manufacturing an optical fiber preform.

Abstract: Embodiments of the invention include a method for making optical fiber having reduced aging or hydrogen aging loss over the life of the fiber and optical fiber systems including such optical fibers. Improved silicon-oxygen stoichiometry during one or more preform manufacturing steps reduces the amount of Si defects generated in the optical fiber preform. Also, deuterium exposure of optical fiber drawn from the preform reduces the likelihood of having atomic defects such as Si defects in the optical fiber that, over time, attract and bond with hydrogen atoms to form molecules that contribute to increased water absorption loss. The inventive method produces optical fibers with improved transmission characteristics, e.g., optical fibers made by methods according to embodiments of the invention have transmission loss at 1385 nanometers that is less than 0.33 dB/km and the aging loss increase thereafter is less than 0.04 dB/km.

Abstract: The invention relates to an optical fibre comprising a gain medium which is equipped with: a core (22) which is formed from a transparent material and nanoparticles (24) comprising a doping element and at least one element for enhancing the use of said doping element; and an outer cladding (26) which surrounds the core. The invention is characterised in that the doping element is erbium (Er) and in that the enhancing element is selected from among antimony (Sb), bismuth (Bi) and a combination of antimony (Sb) and bismuth (Bi). According to the invention, one such fibre is characterised in that the size of the nanoparticles is variable and is between 1 and 500 nanometres inclusive, and preferably greater than 20 nm.

Abstract: A device including at least one gripping member, rotatably mounted about an axis Z-Z, adapted to hold at least one end of at least one elongated element for chemical vapour deposition for forming a preform. The device includes at least one burner being mobile along a direction substantially parallel to the axis Z-Z and adapted to deposit, on the elongated element, a chemical substance for forming a preform, and at least one suction element arranged on the opposite side of the burner on a portion of a wall of the device on the opposite side of the gripping member from the burner. At least one air suction member, mobile along direction Z, is provided with motion synchronous with respect to the burner. The wall with the air suction member has a pair of respective upper and lower tapes rigidly associated with the burner.

Abstract: A method and device for manufacturing a preform for optical fibres through chemical deposition on a substrate for deposition arranged vertically. A chemical deposition chamber includes at least one gripping member rotatably mounted about an axis Z-Z and adapted to hold at least one end of at least one elongated substrate for chemical deposition for the formation of a preform. The chamber includes at least one burner which is mobile along a direction Z substantially parallel to the axis Z-Z and adapted to deposit on the elongated substrate, a chemical substance for the formation of a preform and at least one suction element for collecting exhaust chemical substances. The suction element is arranged on the opposite side of the burner with respect to the axis Z-Z and is mobile along the direction Z and is positioned at a lower height than the burner.

Abstract: The invention concerns a method for making an optical fiber (18) including the following steps: producing a preform (10) containing nanoparticles provided with an active element including at least one recess (14) proximate at least part of the nanoparticles; fiber drawing of the preform (10) by introducing a non-oxidizing gas in the recess (14), thereby limiting the risks of oxidizing the nanoparticles of the preform (10). The preform (10) designed to the manufacture of an optical fiber (18) by the inventive method comprises nanoparticles provided with an active element in a doped zone (12) and at least one recess (14) proximate the doped zone (12).

Abstract: An Outside Vapor Deposition (OVD) apparatus for making an optical fiber preform with uniform deposition of silica particles through uniform heating to the overall length of the preform includes a mandrel having a predetermined length and driven to rotate and a burner for emitting a combustion gas together with a combustion gas toward the mandrel and burning the combustion gas to make silica particles to that the silica particles are deposited on a surface of the mandrel, wherein the burner has a length corresponding to the length of the mandrel and provides uniform temperature throughout the overall length of the mandrel at the same time.

Abstract: The present invention relates to a method for manufacturing an optical preform by employing an internal vapor deposition process. The method uses an energy source and a substrate tube, wherein the energy source is movable over the length of the substrate tube between a point of a reversal at the supply side and a point of a reversal at the discharge side.

Abstract: A method of forming a glass sheet includes obtaining a preform generated from a glass composition and conveying the preform through a channel having a temperature that decreases along a length of the channel to form a glass sheet having a predetermined width and thickness.

Abstract: A known method for producing synthetic quartz glass with a predetermined hydroxyl group content comprises the following steps: a porous SiO2 soot body is produced by flame hydrolysis or oxidation of a silicon-containing start compound and by layerwise deposition of SiO2 particles on a rotating support; the soot body is subjected to a dehydration treatment in a reaction gas-containing drying atmosphere at a drying temperature for removing hydroxyl groups; and the SiO2 soot body is vitrified into a body consisting of the synthetic quartz glass. Starting from this, and in order to permit a reproducible and reliable manufacture of synthetic, UV-radiation resistant quartz glass with predetermined hydroxyl group content and low chlorine content, it is suggested according to the invention that the dehydration treatment according to method step (b) comprises a drying phase during which ozone is used as the reaction gas, whereby the ozone content of the drying atmosphere is between 0.5% by vol. and 10% by vol.

Abstract: A preform for a low loss fiber optic cable and method and apparatus for fabricating such a preform is provided. The method includes providing AlCl3 and CVD precursors and locally doping CaCl3. Alkali and/or alkaline earth fluxing agents can be introduced. The alkali and/or alkaline earths are doped along with the aluminum into the silica glass core.

Abstract: A multi-tube burner is provided which includes a cylindrical outermost nozzle and at least one cylindrical inner nozzle provided coaxially with the outermost nozzle to form annular jet openings for gases used to manufacture a glass preform. The angle between a center axis of an outer circumference of the outermost nozzle and a distal end portion of each of the inner nozzles is 90°± not more than 3°. Furthermore, the distance between the center axis of the outer circumference of the outermost nozzle and each of center axes of inner circumferences and outer circumferences of the inner nozzles is not more than 0.20 mm.

Abstract: An apparatus for fabricating a soot preform for an optical fiber. The soot preform is fabricated by depositing glass particles on a starting rod capable of being rotated and pulled up. The apparatus comprises elements as follows. A reaction chamber is used for depositing the glass particles on the starting rod. An upper room is located above the reaction chamber for receiving the soot preform formed in the upper portion of the reaction chamber. At least one core burner is installed in the reaction chamber. A gas-supplying inlet is located in the top part of the sidewall of the reaction chamber closest to burner(s), and a gas-exhausting outlet is located in the top part of another sidewall opposite to the gas-supplying inlet. In addition, at least one cladding burner is installed in the reaction chamber.

Abstract: The present invention provides an optical fiber preform manufacturing method and a burner apparatus employed for this method. In this manufacturing method, when glass particles are synthesized in an oxy-hydrogen flame emitted from a burner to form a porous optical fiber preform by depositing glass particles in the radial direction of a starting member, the relationship between the flow rate vm (m/sec) of a source material gas or a mixed gas of the source material gas and an additive gas discharged from the burner, and the flow rate vs (m/sec) of an inert gas is such that ?0.06 vm+1.4?vs??0.02 vm+1.8, and vs?0.40, while the relationship between the flow volume Vm (1/min) of the source material gas discharged from the burner and the flow volume Vs (1/min) of the inert gas is such that Vs/Vm?0.2.

Abstract: A waveguide having an angled surface is created by depositing an optical core material onto a substrate having two levels. In one embodiment, a high density plasma deposition may be used to deposit the optical core material.

Abstract: These glass bodies are light weight porous structures such as a boules of high purity fused silica (HPFS). More specifically, the porous structures are supports for HPFS mirror blanks. Porous glass is made utilizing flame deposition of pure silica or doped silica in a manner similar to the production of high purity fused silica. Bubbles or seeds are formed in the glass during laydown. Finely divided silicon carbide (SiC) particles are used to form the bubbles. At least one layer of porous glass is formed in the boule.

Abstract: The invention includes methods of making a fluorine doped soot particle. One method of the invention includes the steps of (1) delivering a silicon containing precursor to a first opening in a burner face; (2) delivering a source of oxygen to a second opening, wherein the second opening is spaced apart from the first opening such that the silicon precursor and oxygen source react to form a soot particle having a surface area of more than about 20 m2/g; and (3) delivering a fluorine precursor to a third opening, said third opening is spaced apart from the first opening. A second method of the invention includes the steps of (A) delivering a silicon containing precursor to a first opening in a burner face; (B) delivering a fluorine precursor to a second opening, wherein said second opening is spaced apart from said first opening; and (C) delivering a fuel to a third opening, said third opening is spaced apart from said first opening.

Abstract: A burner and a method for producing an inorganic soot such as silica comprising a plurality of substantially planar layers having multiple openings therethrough formed by a micromachining process. The openings are in fluid communication with a precursor inlet and a gas inlet to permit the gas and the precursor to flow through and exit the burner. The burner produces a flame from a combustible gas in which the precursor undergoes a chemical reaction to form the soot.

Abstract: A method for feeding a flow of gas to a burner for manufacturing an optical fibre preform. The burner has a plurality of coaxial tubes, each two adjacent coaxial tubes defining an annular channel between themselves; an annular gas distribution chamber at one extremity of the annular channels and in fluid communication therewith, the annular distribution chamber being delimited in the radial direction by an inner and an outer surface. The flow of gas is introduced into the distribution chamber so that the direction of its radially outermost portion is tangential to the radially outer surface of the distribution chamber. The method allows obtaining a better gas velocity distribution in the annular channels.

Abstract: A method and device for manufacturing a preform for optical fibres through chemical deposition on a substrate for deposition arranged vertically. A chemical deposition chamber includes at least one gripping member rotatably mounted about an axis Z-Z and adapted to hold at least one end of at least one elongated substrate for chemical deposition for the formation of a preform. The chamber includes at least one burner which is mobile along a direction Z substantially parallel to the axis Z-Z and adapted to deposit on the elongated substrate, a chemical substance for the formation of a preform and at least one suction element for collecting exhaust chemical substances. The suction element is arranged on the opposite side of the burner with respect to the axis Z-Z and is mobile along the direction Z and is positioned at a lower height than the burner.

Abstract: A method for manufacturing an optical fiber preform includes a process A of applying flame polishing to a center glass rod, a process B of determining a ratio ra/rb, which is a ratio of a radius ra of the center glass rod expressed in millimeters with respect to a radius rb of a target optical fiber preform expressed in millimeters, based on a refractive index profile of a target optical fiber preform, and a process C of determining an amount of fine glass particles to be deposited on the center glass rod so that a ratio ra/rb/c falls within a range from 0.002 to 0.01, where “c” is a maximum value of hydroxyl group concentration expressed in ppm in the vicinity of a boundary between the center glass rod and an outer layer, which is formed by depositing fine glass particles on the center rod and by being vitrified.

Abstract: A method for manufacturing a glass base material for an optical fiber by forming a core rod having a core section and a portion of a clad, forming an additional clad by depositing glass particles on circumference of the core rod, and performing a sintering and vitrifying process on an obtained porous base material, includes the step of forming the core rod in order that the relation 3.75≦a/m≦6 is satisfied, where ‘a’ denotes an outer diameter of a section corresponding to the core rod, and ‘m’ denotes a mode field diameter at 1385 nm in wavelength with regard to the optical fiber obtained by drawing the glass base material.

Abstract: This invention relates to the production of high purity fused silica glass through oxidation or flame hydrolysis of a vaporizable silicon-containing compound. More particularly, this invention is directed to the use of vaporizable, halide-free compounds in said production. In the preferred practice, a polymethylsiloxane comprises said vaporizable, halide-free compound.