Autoionizing states driven by stochastic electromagnetic fields

Abstract

We have examined the profile of an isolated autoionizing resonance driven by a pulse of short duration and moderately strong field. The analysis has been based on stochastic differential equations governing the time evolution of the density matrix under a stochastic field. Having focused our quantitative analysis on the 2s2p( 1 P ) resonance of Helium, we have investigated the role of field fluctuations and of the duration of the pulse. We report surprisingly strong distortion of the profile, even for peak intensity below the strong field limit. Our results demonstrate the intricate connection between intensity and pulse duration, with the latter appearing to be the determining influence, even for a seemingly short pulse of 50 fs. Further effects that would arise under much shorter pulses are discussed.PACS numbers: 32.80. Aa, 32.80.Hd, 32.70.Jz, 32.80.Rm Autoionizing (AI) states, also referred to as resonances, in atoms and molecules belong to a rich field of Atomic Molecular and Optical (AMO) physics, representing a paradigm of discrete states embedded in continua. Typically, they can be excited either by photoabsorption or by collisions. The literature on the subject is vast, but luckily a relatively recent review [1] provides an interesting guide to the origins of the field, as well as a substantial collection of references to both theoretical and experimental work. The simplest case in point is represented by a so-called "isolated AI resonance", which means that the width of its excitation profile is much smaller than the energy distance from the nearest AI resonance. A textbook example of an isolated resonance is provided by the doubly excited 2s2p( 1 P ) state of Helium, which has been studied in exhaustive detail, both theoretically and experimentally, over the last 60 or so years [1]. The field has more recently been enriched with fascinating details on the temporal evolution of AI through the exploitation of coherent few cycle pulses [2,3,4].Traditional photoabsorption studies of AI resonances have been carried out mainly by means of synchrotron radiation, where weak, practically monochromatic radiation excites the resonance. The most easily observed quantities, as a function of the arXiv:1707.09172v1 [physics.atom-ph]

Strong-Field Extreme-Ultraviolet Dressing of Atomic Double Excitation

“…2. We note that changes of the resonance profile have also been predicted by recent theoretical calculations [25][26][27], whereas here we identify the mechanism of dressing-induced phase shifts on a timescale shorter than the autoionization lifetime, which we believe is the main reason for twisting the Fano line into a more symmetric shape with higher XUV photon fluence.…”

“…On the other hand, strongly driving an autoionizing state directly with intense short-wavelength fields, as proposed theoretically in [11,12], has not been demonstrated experimentally. Very recently, this topic has received new theoretical interest [25][26][27], now coming experimentally within reach with state-of-the-art FEL pulses. The latter have nowadays indeed become the workhorse for the study of resonant nonlinear light-matter interaction in the XUV and x-ray spectral domain [28][29][30][31][32][33][34][35].…”

Effects of field fluctuations on driven autoionizing resonances

“…Moreover the complete theory of an AI resonance driven strongly by a stochastic field, with intensity fluctuations, poses challenging problems not readily amenable to the theoretical tools developed for strongly driven transitions between bound states [2]. In a recent short paper [13], we have reported a first assessment of the basic effects to be expected. The present paper provides a more detailed exposition of the theory, as well as a partial account of the effect of intensity fluctuations.…”

Resonances in the Hulthén potential: benchmark calculations, critical behaviors, and interference effects

“…The nature of resonances, which includes, e.g. their creation and decay, radiative or non-radiative interaction with the bound and continuum spectra as well as other resonances [6,7], and their evolution under external environment or electromagnetic fields [8][9][10][11] still inspires fascinating research that enriches our understanding of the fundamental properties of quantum systems.…”