  We propose supercritical xenon in a hollow-core photonic bandgap fiber as a
highly nonlinear medium, and demonstrate 200 nm control over the guidance
window of the fiber as the xenon goes through its supercritical phase
transition. The large optical polarizability and monoatomic nature of xenon are
predicted to allow large optical nonlinearity, on the same order as that of
fused silica, while maintaining greatly reduced Raman scattering, offering
benefits for nonlinear and quantum optics.
