A technique for optically accessing ultra-high vacuum environments, via a photonic-crystal fiber with a long small hollow core, is described. The small core and the long bore enable a pressure ratio of over 10-8 to be maintained between two environments, while permitting efficient and unimpeded delivery of light, including ultrashort optical pulses. This delivery can be either passive or can encompass nonlinear optical processes such as optical pulse compression, deep UV generation, supercontinuum generation, or other useful phenomena.
Ermolov, A., Mak, K. F., Tani, F., Hölzer, P., Travers, J. C., & Russell, P. S. J. (2013). Low loss hollow optical-waveguide connection from atmospheric pressure to ultra-high vacuum. Applied Physics Letters, 103(26), . https://doi.org/10.1063/1.4860947