Long-Lived Refractive-Index Changes Induced by Femtosecond Ionization in Gas-Filled Single-Ring Photonic-Crystal Fibers

Plasma recombination always follows photoionization of gas by intense femtosecond laser pulses, causing refractive-index changes via thermal and hydrodynamic effects. In gas-filled hollow-core photonic-crystal fibers, these phenomena are induced by self-compressing pulses with μJ energies. Probing from the side of the fiber, the authors see refractive-index changes lasting tens of μs, and plasma-driven acoustic waves that excite MHz vibrations in the microstructure of the fiber. These results are important for the development of high-intensity, high-repetition-rate lasers where, in addition to nonlinear optics, plasma physics and optoacoustics also become relevant.