Patent ID: 6920766

Claim:
An apparatus for producing a synthetic quartz glass preform by flame hydrolysis which is adapted for application of high-energy DUV-radiation in the wavelength range under 250 nm, has a leading plateau surface followed by a parabolic surface which is followed by a cylindrical surface, a core with an OH-content of ≧1150 ppm, a strain birefringence of ≦5 nm/cm, a H 2 -content of ≧1·10 18 molecules/cm 3 , a CI-content of ≦20 ppm, an amount of contaminating trace elements Cr, Co, Fe, Ni, Cu, V, Zn, Al, Li, K, Na up to 500 ppb and which is substantially free of stratifications, and has a stability of which towards high-energy DUV-radiation is given by a transmissions reduction of ΔT ≦0.1%/cm thickness, when the synthetic quartz glass is subjected to the following radiation, wavelength λ 1 =248 nm, laser shot frequency ≧300 Hz, laser shot rate ≧10 9 , and energy density ≦10 mJ/cm 2 , as well as wavelength λ 2 =193 nm, laser shot frequency ≧300 Hz, laser shot rate ≧10 9 , and energy density ≦5 mJ/cm 2 , the apparatus comprising: a burner having nozzles providing a silicon compound, hydrogen and oxygen and forming melted particles of a silicon composition at a temperature of at least 2,000° C.; a preform supporting arrangement for rotatably supporting the preform to rotate about a horizontal rotation axis; a horizontally arranged muffle, the muffle comprising an internal chamber extending horizontally, a larger opening and a smaller opening communicating with the chamber on opposite horizontal sides of the muffle; the larger opening being adapted for removing the preform and being open for exhausting gases; the smaller one for receiving the burner and being open around the burner for intaking air from the surrounding environment; the chamber substantially gradually narrowing from the larger opening to the smaller opening, the chamber having a parabolic portion adapted to envelope the parabolic surface of said preform at a distance “a” in the range of 5 mm to 100 mm, at least said parabolic portion being at least approximately rotation-symmetrical to the axis of rotation of said preform; and the burner being disposed opposite the plateau surface at a position having a central burner axis offset from and substantially parallel to the horizontal rotation axis so as to deposit the melted particles at a temperature of at least 2,000° C. on the plateau surface.