Effects of Field Fluctuations on Driven Autoionizing Resonances

TL;DR

This paper develops a time-dependent theoretical framework to describe the excitation of autoionizing resonances by intense, fluctuating radiation sources like free electron lasers, revealing complex effects beyond traditional models.

Contribution

It introduces a systematic approach to account for pulse shape, duration, and stochastic fluctuations in modeling autoionizing resonance excitation.

Findings

Intensity fluctuations significantly alter excitation profiles.

Traditional Fano profiles are insufficient under intense, fluctuating fields.

Theoretical challenges of modeling stochastic effects are addressed.

Abstract

The excitation of an autoionizing resonance by intense radiation requires a theoretical description beyond the transition probability per unit time. This implies a time-dependent formulation incorporating all features of the radiation source, such as pulse temporal shape and duration, as well as stochastic properties, for pulses other than Fourier limited. The radiation from short wavelength free electron lasers is a case in point, as it is the only source that can provide the necessary intensity. In view of ongoing experiments with such sources, we present a systematic study for an isolated autoionizing resonance. We find that intensity, pulse duration and field fluctuations conspire in producing unexpected excitation profiles, not amenable to a description in terms of the usual Fano profile. In particular, the role of intensity fluctuations turns out to pose challenging theoretical problems part of which have been addressed herein.