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A known method for producing a hollow cylinder of synthetic quartz glass comprises the steps of: (a) providing an inner tube of synthetic quartz glass having an inner bore defined by an inner wall, (b) cladding the inner tube (3′) with an SiO2 soot layer (4′), and (c) sintering the SiO2 soot layer w

A known method for producing a hollow cylinder of synthetic quartz glass comprises the steps of: (a) providing an inner tube of synthetic quartz glass having an inner bore defined by an inner wall, (b) cladding the inner tube (3′) with an SiO2 soot layer (4′), and (c) sintering the SiO2 soot layer with formation of the hollow cylinder. Starting therefrom, to indicate a method in which on the one hand the sintering process is completed before the hollow cylinder is further processed together with the core rod, and in which on the other hand a complicated machining of the inner bore of the hollow cylinder of quartz glass is not required, the invention suggests that during sintering the surface temperature of the inner wall of the inner tube should be kept below the softening temperature.

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1. A method for producing a hollow cylinder of synthetic quartz glass, said method comprising: a) providing an inner tube of synthetic quartz glass having an inner bore defined by an inner wall;b) cladding the inner tube with an SiO2 soot layer;c) sintering the SiO2 soot layer so as to form the holl

1. A method for producing a hollow cylinder of synthetic quartz glass, said method comprising: a) providing an inner tube of synthetic quartz glass having an inner bore defined by an inner wall;b) cladding the inner tube with an SiO2 soot layer;c) sintering the SiO2 soot layer so as to form the hollow cylinder; wherein, during sintering, the inner wall of the inner tube has a surface temperature that is kept below a softening temperature; and wherein during sintering, the surface temperature of the inner wall of the inner tube is less than 1400° C. 2. The method according to claim 1, wherein the quartz glass of the inner tube has a lower cooling temperature, and, during sintering, the surface temperature of the inner wall is greater than the lower cooling temperature of the quartz glass of the inner tube. 3. A method for producing a hollow cylinder of synthetic quartz glass, said method comprising: d) providing an inner tube of synthetic quartz glass having an inner bore defined by an inner wall;e) cladding the inner tube with an SiO2 soot layer;f) sintering the SiO2 soot layer so as to form the hollow cylinder; wherein, during sintering, the inner wall of the inner tube has a surface temperature that is kept below a softening temperature; and wherein the inner wall is subjected to forced cooling. 4. The method according to claim 3, wherein the forced cooling comprises passing a cooling fluid or gas through the inner bore. 5. The method according to claim 4, wherein the cooling fluid or gas is a hydrogen-free inert gas. 6. The method according to claim 3, wherein a cooling fluid or gas is conducted in a closed cooling circuit in the forced cooling. 7. The method according to claim 1, wherein the inner tube has a wall thickness of less than 20 mm. 8. The method according to claim 1, wherein the soot layer is vitrified in a zone type sintering method. 9. The method according to claim 1, wherein the inner wall is produced without use of any tools in a melt. 10. The method according to claim 1, wherein, after sintering, the hollow cylinder of quartz glass is subjected to an annealing process. 11. The method according to claim 1, wherein an inner wall of the hollow cylinder of quartz glass is cleaned after vitrification. 12. A method for producing a hollow cylinder of synthetic quartz glass, said method comprising: g) providing an inner tube of synthetic quartz glass having an inner bore defined by an inner wall;h) cladding the inner tube with an SiO2 soot layer;i) sintering the SiO2 soot layer so as to form the hollow cylinder; wherein, during sintering, the inner wall of the inner tube has a surface temperature that is kept below a softening temperature; and wherein the quartz glass of the inner tube contains a dopant effecting a reduction of the refractive index. 13. The method according to claim 1, wherein the inner tube of quartz glass has a hydroxyl group content of less than 1 wt ppm. 14. The method according to claim 1, and further comprising providing the hollow cylinder obtained according to said method step (c) as the inner tube in performing a subsequent iteration of method steps (a) and (b). 15. A method for producing a hollow cylinder of synthetic quartz glass, said method comprising: j) providing an inner tube of synthetic quartz glass having an inner bore defined by an inner wall;k) cladding the inner tube with an SiO2 soot layer;l) sintering the SiO2 soot layer so as to form the hollow cylinder; wherein, during sintering, the inner wall of the inner tube has a surface temperature that is kept below a softening temperature; and wherein the inner tube has one or more inner bores of an oval or polygonal cross section. 16. A method for producing an optical component, said method comprising: producing a hollow cylinder of synthetic quartz glass includingproviding an inner tube of synthetic quartz glass having an inner wall defining an inner bore;cladding the inner tube with an SiO2 andsintering the SiO2 soot layer so as to form the hollow cylinder;fixing a core rod in the inner bore of the hollow cylinder so as to form a coaxial arrangement; andelongating the coaxial arrangement into the optical component, wherein, during the sintering of SiO2 soot layer, the inner wall of the inner tube has a surface temperature that is kept below a softening temperature; andwherein during sintering, the surface temperature of the inner wall of the inner tube is less than 1400° C. 17. The method according to claim 16, wherein the quartz glass of the inner tube has a lower cooling temperature, and during sintering, the surface temperature of the inner wall is greater than the lower cooling temperature of the quartz glass of the inner tube. 18. The method according to claim 1, wherein during sintering, the surface temperature of the inner wall of the inner tube is less than 1250° C. 19. The method according to claim 1, wherein the inner tube of quartz glass has a hydroxyl group content of less than 0.1 wt ppm. 20. The method according to claim 16, wherein during sintering, the surface temperature of the inner wall of the inner tube is less than 1250° C.