Abstract: A monochromatic light beam scans a silica reference and a translucent body, both submerged in index matching fluid and the deflection angle of the beam is measured as it exits the reference, the translucent body and the fluid. This deflection angle of the light beam exiting the reference is compared with the undeflected beam passing through only the fluid. The difference, if any, is used to offset the measurements of the deflection angles of the light beam exiting the translucent body to correct them so that the profile is referenced to the index of silica.

Abstract: Undeposited reactants (i.e., soot) passing through a glass substrate tube (12), during the fabrication of a lightguide perform by the Modified Chemical Vapor Deposition (MCVD) process, flow into a reactant exhaust system (50) and are carried therethrough by a uniformly flowing reactant-free gas. The reactants pass through an exhaust tube (52), a reactant collection chamber (54), through a pressure control apparatus (56;114) and into a gas scrubber. The pressure within the exhaust system (50) is maintained substantially constant during the MCVD process by continuously monitoring the pressure therein and adjusting the pressure control apparatus (56;114) accordingly. Additionally, a continuous, uniform flow of soot-free gas is directed into the exhaust system to assist in the removal of the undeposited reactants therefrom.