High vacuum compatible fiber feedthrough for hot alkali vapor cells

We demonstrate a method to produce vacuum tight, metal free, bakeable and alkali compatible feedthroughs for optical fibers. The manufacturing process mainly relies on encasing fibers made of fused silica with glass materials with lower melting points by heating. We analyze the vacuum and optical performance of the devices by various methods including helium leak checking and several spectroscopic schemes, among others electromagnetically induced transparency involving Rydberg states.