Experimental Separation of Subcycle Ionization Bursts in Strong-Field Double Ionization of H2

Abstract

We report on the unambiguous observation of the subcycle ionization bursts in sequential strong-field double ionization of H 2 and their disentanglement in molecular frame photoelectron angular distributions. This observation was made possible by the use of few-cycle laser pulses with a known carrier-envelope phase, in combination with multiparticle coincidence momentum imaging. The approach demonstrated here will allow sampling of the intramolecular electron dynamics and the investigation of charge-statespecific Coulomb distortions on emitted electrons in polyatomic molecules.

Exploring photoelectron angular distributions emitted from molecular dimers by two delayed intense laser pulses

“…Thus, one of the results of this study is that DFPADs can, with adaptations, be read in a similar way as MFPADs. Furthermore, by applying methods based on angular streaking developed previously [9,13,14] and with the support from semiclassical trajectory simulations we are able to show that the dominant process underlying the rotation is scattering of the second-emitted electron on the neighboring molecular ion as it is driven away by the strong laser field. This finding adds to the emerging evidence for the key importance of laser-subcycle electron scattering dynamics in strong-field driven dimers [29] and clusters [33].…”

“…The reaction microscope used in our experiments to measure in coincidence the momenta of two molecular ions and two electrons emerging from the interaction of a sequence of two intense laser pulses with a cold jet of molecules generated by ultrasonic expansion of N 2 and O 2 gas is described elsewhere [9,13,14]. The laser pulses used in the experiments had both a central wavelength of 790 nm and a duration of about 25fs.…”

“…If combined with coincidence imaging of the photoion momenta, this technique allows for the measurement of molecular frame photoelectron angular distributions (MFPADs) of a single molecule, which can provide unique insight into the intramolecular dynamics with femtosecond resolution [3]. This method can also be implemented with an intense, elliptically polarized laser pulse as the ionizing probe [4][5][6][7][8][9]. In that case, the rotating electric field vector of the probe pulse can be exploited for mapping laser-subcycle time to electron momentum, a concept known as angular streaking [9][10][11][12][13][14].…”

“…This method can also be implemented with an intense, elliptically polarized laser pulse as the ionizing probe [4][5][6][7][8][9]. In that case, the rotating electric field vector of the probe pulse can be exploited for mapping laser-subcycle time to electron momentum, a concept known as angular streaking [9][10][11][12][13][14]. When distortions of the such obtained MFPADs due to the parent ion's Coulomb potential [5,7], the field-driven electronic dynamics [6], or the nuclear dynamics [9,13] that take place concomitantly with the photoelectron emission are properly accounted for, molecular dynamics can be extracted from them with subfemtosecond resolution.…”

“…In this article we describe experiments and simulations performed with the aim of investigating to what extent photoelectron angular distributions (PADs) measured with a strong, elliptically polarized laser field can be used to extract structural and dynamical information from molecules bound in a heterodimer complex. To this end we studied with a reaction microscope [9,13,14,31,32] the PADs from sequential double ionization of N 2 -N 2 and N 2 -O 2 dimers during two delayed intense laser pulses in coincidence with the photoions ejected during subsequent fragmentation of the dimers. Our main concern was to understand which information about the laser-molecule interaction is contained in the measured PADs and how this information can be extracted.…”