Before you set up the preform, I recommend leak testing the rotary seal. I do this by flowing oxygen through the rotary seal. Start by plugging the end of the rotary seal with a solid quartz tube. Next, lower the regulated O2 pressure to ~ 5 psi, slightly above what the system will see during deposition. Observing the O2 carrier mass flow controller, you will see it go to zero if the system is leak tight. This procedure will leak test the oxygen carrier line throughout the gas system, from input to rotary seal. Taking time to conduct this leak test is worthwhile. If a leak is present in the rotary seal, you can potentially add moisture and/or lose part of the gas stream, which would reduce layer thickness and potentially refractive index. If the leak rate changes during the run, it can result in axial preform variability.

 

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