Abstract
The photoionization of Lithium (Li+) via its doubly-excited state 2s2p 1P in intense free electron laser (FEL) radiation is studied. A recently developed perturbative statistical description of the atomic dynamics is used to calculate the ionization yield. It is observed that the FEL temporal fluctuations affect the lineshape significantly, strongly dependent on the product of the pulse’s coherence time with its intensity, ∼τcI0, which is a measure of the effect of the field in one correlation time. The weak-field long-pulse asymmetric resonant Fano-profile is broadened to resemble a Voight profile. As the intensity increases, the subsequent ionization of Li2+ takes over and causes further distortion of the lineshape for Li+.
Highlights
The advent of high-order harmonic generation (HOHG) and Free-Electron Laser (FEL) sources in the last two decades has made available radiation which is sufficiently short to compete with sub-femtosecond atomic characteristic times and sufficiently intense to compare and surpass the static interatomic electric fields by orders of magnitudes [1,2,3,4,5]
An important characteristic of this radiation is that it can spatially penetrate the interior of atomic-size systems and interact with the innermost electrons directly; a property which is in complete contrast with intense, long-wavelength, laser (i.e., Ti:Sapphire) where the outermost electrons act as a shield and disallow probe of the inner regions even if the necessary energy is available in the form of multiphoton absroptions
In the present work we investigate the lineshape of the ionization of Li+ for FEL fields in the proximity of the 2s2p1 P autioinization resonance (AIS)
Summary
The advent of high-order harmonic generation (HOHG) and Free-Electron Laser (FEL) sources in the last two decades has made available radiation which is sufficiently short to compete with sub-femtosecond atomic characteristic times and sufficiently intense to compare and surpass the static interatomic electric fields by orders of magnitudes [1,2,3,4,5]. In the case of ionization with FEL sources very often the measurements of observables are taken after the target systems have interacted many times with pulses which differ each other in random ways (multishot experiments); the experimental reports provide only statistically averaged values of the observables. For this class of experiments it is inevitable that the temporal fluctuations in the atomic photoionization dynamics should be properly taken into account, in principle, for a fair comparison with the experimental data. For the presentation of the formulas, atomic units (a.u.) are used throughout the text; For the reader’s convenience other units (e.g., eV, fs) are used in the discussion section and the figures caption
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