Long-lived refractive index changes induced by femtosecond ionization in gas-filled single-ring photonic crystal fibers

TL;DR

This study reveals that femtosecond ionization in gas-filled photonic crystal fibers causes long-lasting refractive index changes and mechanical vibrations, influencing high-repetition-rate laser pulse propagation.

Contribution

It demonstrates the long-lived nature of ionization-induced index changes and mechanical oscillations, and how gas choice affects ionization and subsequent optical effects in fiber systems.

Findings

Refractive index changes last for tens of microseconds.

Mechanical vibrations occur at megahertz frequencies.

Lighter gases reduce ionization and index change strength.

Abstract

We investigate refractive index changes caused by femtosecond photoionization in a gas-filled hollow-core photonic crystal fiber. Using spatially-resolved interferometric side-probing, we find that these changes live for tens of microseconds after the photoionization event - eight orders of magnitude longer than the pulse duration. Oscillations in the megahertz frequency range are simultaneously observed, caused by mechanical vibrations of the thin-walled capillaries surrounding the hollow core. These two non-local effects can affect the propagation of a second pulse that arrives within their lifetime, which works out to repetition rates of tens of kilohertz. Filling the fiber with an atomically lighter gas significantly reduces ionization, lessening the strength of the refractive index changes. The results will be important for understanding the dynamics of gas-based fiber systems operating at high intensities and high repetition rates, when temporally non-local interactions between successive laser pulses become relevant.