Extreme Ultraviolet Superfluorescence in Xenon and Krypton

TL;DR

This study demonstrates superfluorescence in the extreme ultraviolet range from xenon and krypton gases induced by high-intensity free-electron laser pulses, combining experimental observations with a new quantum theoretical model.

Contribution

It provides the first comprehensive experimental and theoretical analysis of EUV superfluorescence in noble gases, highlighting the role of inner-shell ionization and Auger decay.

Findings

Superfluorescent emission observed in Xe and Kr gases.

Emission intensity grows exponentially with increased pressure or pump energy.

Line broadening correlates with superfluorescence yield.

Abstract

We present a comprehensive experimental and theoretical study on superfluorescence in the extreme ultraviolet wavelength regime. Focusing a high-intensity free-electron laser pulse in a cell filled with Xe or Kr gas, the medium is quasi instantaneously population-inverted by inner-shell ionization on the giant resonance followed by Auger decay. On the timescale of 100 ps a macroscopic polarization builds up in the medium, resulting in superfluorescent emission of several Xe and Kr lines in the forward direction. As the number of emitters in the system is increased by either raising the pressure or the pump-pulse energy, the emission shows an exponential growth of over 4 orders of magnitude and reaches saturation. With increasing yield, we observe line broadening, a manifestation of superfluorescence in the spectral domain. Our novel theoretical approach, based on a full quantum treatment of the atomic system and the irradiated field, shows quantitative agreement with the experiment and supports our interpretation.