Angle-resolved RABBITT: theory and numerics

Abstract

I. ABSTRACTAngle-resolved (AR) RABBIT measurements offer a high information content measurement scheme, due to the presence of multiple, interfering, ionization channels combined with a phase-sensitive observable in the form of angle and time-resolved photoelectron interferograms. In order to explore the characteristics and potentials of AR-RABBIT, a perturbative 2-photon model is developed; based on this model, example AR-RABBIT results are computed for model and real systems, for a range of RABBIT schemes. These results indicate some of the phenomena to be expected in AR-RABBIT measurements, and suggest various applications of the technique in photoionization metrology. Article history• arXiv (this version) The RABBIT methodology -"reconstruction of attosecond harmonic beating by interference of two-photon transitions" [1] -essentially defines a scheme in which XUV pulses are combined with an IR field, and the two fields are applied to a target gas. The gas is ionized, and the photoelectrons detected. In the typical case, the IR field is at the same fundamental frequency ω as the field used to drive harmonic generation, and the XUV field generated is an atto-second pulse train with harmonic components nω, with odd-n only. In this case, if the intensity of the IR field is low to moderate, the resultant photoelectron spectrum will be comprised of discrete bands corresponding to direct 1-photon XUV ionization, * paul.hockett@nrc.ca and sidebands corresponding to 2-photon XUV+IR transitions [1]. (The energetics of this situation are illustrated in fig. 1.) Temporally, if the XUV pulses are short relative to the IR field cycle, the sidebands will also show significant time-dependence, since they will be sensitive to the optical phase difference between the XUV and IR fields, with an oscillatory frequency of 2ω. In this case, a measurement which is angle-integrated, or made at a single detection geometry, can be viewed as a means to characterising the properties of the XUV pulses (spectral content and optical phase), provided that the ionizing system is simple or otherwise well-characterised [1]; RABBIT can therefore be utilised as a pulse metrology technique [1,2], and this is the typical usage.Conversley, RABBIT can also be regarded as a photoelectron metrology technique, since it is sensitive to the magnitudes and phases of the various photoionization pathways accessed. In contrast to most traditional (energy-resolved) photoelectron spectroscopy techniques, RABBIT has the distinction of interfering pathways resulting from different 1-photon transition energies: it is thus sensitive to the energy-dependence of the photoionization dynamics, as well as to the partial-wave components within each pathway. An angle-resolved (AR) RABBIT measurement is particularly powerful in this regard, since the partial-wave phases are encoded in the angular part of the photoelectron interferogram. Although this is a potentially powerful technique, the underlying photoionization dynamics may be extremely complicated, hence quantitati...

Time delays from one-photon transitions in the continuum

“…For such continuumcontinuum transitions, we measure a delay between outgoing s-and d-electrons as large as 12 as close to the ionisation threshold in helium. Both single-active-electron and first-principles ab initio simulations confirm this observation for helium and hydrogen, demonstrating the universality of the observed delays.Recently, experimental evidence of a strong effect of the IR-induced cc-transitions on the angular dependence of the total photoemission delays has been reported [14,15] stimulating several independent investigations on the origin of this effect [21,[23][24][25][26][27]. In this work, arXiv:1907.03607v1 [physics.atom-ph]…”

“…Recently, experimental evidence of a strong effect of the IR-induced cc-transitions on the angular dependence of the total photoemission delays has been reported [14,15] stimulating several independent investigations on the origin of this effect [21,[23][24][25][26][27]. In this work, arXiv:1907.03607v1 [physics.atom-ph]…”

Attosecond-resolved photoionization of chiral molecules

“…To find signatures of chirality in the photoionization delays, we resolved the angular dependence of the photoionization dynamics (14,37,38). We integrated the photoelectron signal in slices of 10°around different ejection angles a from the polarization plane of the light and then measured the associated delays (Dt cc f/b ).…”

Simulation of angular-resolved RABBITT measurements in noble-gas atoms

“…These experiments bring sensitive information on ultrafast electron dynamics influenced by correlation and exchange effects. Theoretical modeling of the angular resolved RABBITT process have been provided within the framework of lowest order perturbation theory (LOPT) [4,5] and non-perturbatively, by solving the time-dependent Schrödinger equation (TDSE) [2,6]. As in our preceding paper [6], we solved TDSE for a noble gas atom (He and Ne) driven by an ionizing XUV and dressing IR fields in the configuration of a typical RABBITT measurement.…”