Patent ID: 8137469

Claim:
A process for making doped or undoped silica glass material, comprising the following steps: (I) providing at least one stream of glass soot particles comprising silica via a soot-generating device; and (II) directing the at least one stream of glass soot particles to an essentially planar deposition supporting surface of a deposition substrate rotatable about a rotation axis, such that at least one layer of glass soot is deposited on the deposition supporting surface to form a soot preform, said layer having an area A 1 and a thickness T 1 ; wherein in step (II), the deposition supporting surface has an essentially uniform temperature such that the temperature of the deposition support surface is within ±25° C. of an average temperature and wherein the deposition supporting surface is heated to a temperature of between 500° C. and 1000° C. by an active heating source adjacent to a side of the substrate opposite the deposition supporting surface and having controllable heating power, wherein the active heating source is a planar susceptor of an induction heating system and has a surface that forms a flat plane free of an opening or aperture and is adjacent to the side of the deposition support surface, wherein a layer of refractory felt is disposed between the substrate and the active heating component, and wherein the soot-generating device is allowed to move relative to the deposition supporting surface, and the velocity of the soot-generating device relative to the deposition supporting surface is modulated such that in at least half of the area of the layer of glass soot deposited and through at least the center half thickness, local soot density variation is low.