Heteronuclear Limit of Strong-Field Ionization: Laser-Induced Fragmentation of HeH<sup>+</sup>

Wustelt, Philipp; Oppermann, Florian; Yue, Lun; Möller, Max; Stöhlker, Thomas; Lein, Manfred; Gräfe, Stefanie; Sayler, A. M.; Paulus, Gerhard G.

doi:10.1109/cleoe-eqec.2019.8872835

Cited by 3 publications

(6 citation statements)

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“…The measured DI yields in Fig. 3(j) are also aligned, with KER 8-25 eV, corresponding to the second ionization event occuring between R ∼ 5 − 25 [51]. The simulation with T = 3500 K in Fig.…”

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confidence: 70%

“…The experimental setup is identical to that described in Ref. [51]. Briefly, the HeH + ions are synthesized in a duoplasmatron ion source, accelerated to 10 keV kinetic energy, and focused towards the laser interaction region, where a tabletop Ti:Sapphire laser system provides 800nm-pulses with peak intensities of up to 10 17 W/cm 2 and intensity full width at half maximum duration τ ∼ 34 fs.…”

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confidence: 99%

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Strong-field polarizability-enhanced dissociative ionization

et al. 2018

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We investigate dissociative single and double ionization of HeH + induced by intense femtosecond laser pulses. By employing a semi-classical model with nuclear trajectories moving on field-dressed surfaces and ionization events treated as stochastical jumps, we identify a strong-field mechanism wherein the molecules dynamically align along the laser polarization axis and stretch towards a critical internuclear distance before getting dissociative ionized. As the tunnel-ionization rate is greater for larger internuclear distance and for aligned samples, ionization is enhanced. The strong dynamical rotation is traced back to a maximum in the parallel component of the internucleardistance-dependent polarizability tensor. Qualitative agreement with our experimental observations is found. Finally the criteria for observing the isotope effect for the ion angular distribution is discussed.PACS numbers: 33.80. Wz, 33.80.Eh, 42.50.Hz The ionization and dissociation of small molecules in intense laser fields is of fundamental interest and has captured the attention of physicists for many years [1][2][3]. When the ratio of the laser frequency to the peak electric field is sufficiently small, the ionization process can be considered as an electron tunneling through the instantaneous barrier formed by the field and the Coulomb potential of the system [4]. In molecules, such tunnelionization rates depend on the spatial separation between the nuclei [5-9], as well as the molecular orientation with respect to the laser polarization axis, where the ionization rate follows the shape of the highest-occupied molecular orbital [10][11][12]. In addition to these fixed-nuclei properties, the molecules will dynamically rotate and stretch in the field, potentially leading to fragmentation [8]. Here, we theoretically identify a new fragmentation pathway that involves the combination of the aforementioned strong-field dynamics. Namely, due to the force resulting from the internuclear-distance-dependent polarizability tensor, the molecule is simultaneously aligned and stretched towards a specific internuclear distance in the field-dressed ground state before being ionized. We denote it as polarizability-enhanced dissociative ionization (PEDI) and support our findings with experimental data.Polarizability effects have been explored extensively in strong-field physics, e.g. it has regularly appeared in the interpretation of strong-field ionization experiments [13,14], and the anisotropic polarizability is often exploited in molecular alignment experiments [15][16][17]. In dissociative ionization studies involving short laser pulses (tens of femtoseconds (fs) duration), often only the vibrational degrees of freedom are considered, while the rotational dynamics are disregarded. This is based on the intuition that the field-free rotational timescale of picoseconds is much greater than the vibrational timescale of fs and thus rotational motion can be safely neglected.However, as several works employing semiclassical methods [7,18,19] have show...

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Strong-field polarizability-enhanced dissociative ionization

et al. 2018

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“…In the case of polar (asymmetric) molecules on the contrary, the fragment ejection direction in asymmetric laser fields has been exclusively explained by the anisotropy of the tunneling ionization rate, which is determined by the shape of the ionizing molecular orbital (usually the highest occupied molecular orbital, HOMO) and the molecule's permanent dipole moment (Ohmura and Tachiya, 2008;Holmegaard et al, 2010;Dimitrovski et al, 2011;Li et al, 2011;Wu et al, 2012;Ohmura et al, 2014;Li et al, 2016;Wustelt et al, 2018;Yue et al, 2018;Endo et al, 2019;Ohmura et al, 2019), rather than by post-ionization interactions. Although post-ionization interactions should be important even for the dissociation of polar molecules, their contributions are generally buried under the strong anisotropy of the tunneling ionization rate.…”

Section: Introductionmentioning

confidence: 99%

Post-Ionization Dynamics of the Polar Molecule OCS in Asymmetric Laser Fields

et al. 2022

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We have investigated the dissociation mechanisms of the prototypical heavy polar molecule OCS into the two break-up channels of the dication, OCS2+ → O+ + CS+ and OC+ + S+, in phase-locked two-color intense laser fields. The branching ratio of the breaking of the C–O and C–S bonds followed a pronounced 2π-oscillation with a modulation depth of 11%, depending on the relative phase of the two-color laser fields. The fragment ejection direction of both break-up channels reflects the anisotropy of the tunneling ionization rate, following a 2π-periodicity, as well. The two dissociation pathways in the C–S bond breaking channel show different phase dependencies of the fragment ejection direction, which are assigned to post-ionization dynamics. These observations, resulting from the excitation with asymmetric two-color intense laser fields, supported by state-of-the-art theoretical simulations, reveal the importance of post-ionization population dynamics in addition to tunneling ionization in the molecular fragmentation processes, even for heavy polar molecules.

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“…For the asymmetric system, the TDSE simulations of strong-field ionization dynamics can be more easily executed. Moreover, it can also be manipulated in present strong-filed experiments [29]. Due to the effect of PD, the HeH + system in strong laser fields stretches rapidly toward larger internuclear distances R and the ionization of the molecule also mainly occurs at larger R [30].…”

Section: Methodsmentioning

confidence: 99%

“…For shorter laser wavelengthes, some electrons which are located in the ground state are pumped into then ionized from the first excited state, and the excited-state ionization channel therefore has an important role in strong-field dynamics of HeH + [32]. Here, we focus on longer wavelengthes (longer than 800 nm) for which the Stark-shifted ground-state channel, as introduced in figure 1, dominates in ionization [28,29].…”

Section: Offset Angles Of Heh +mentioning

confidence: 99%

Measuring ionization time lag of polar molecules with a calibrated attoclock

et al. 2023

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Electrons in atoms and molecules can not respond immediately to the action of intense laser field. There is a time lag (about 100 attoseconds) between instants of the field maximum and the ionization-rate maximum. This lag characterizes the response time of the electronic wave function to a strong-field ionization event and has important effects on dynamics of the ionized electron. For polar molecules with a large permanent dipole, the direct measurement or calculation of the absolute time lag is difficult. Here, a calibrated attoclock procedure, which is related to a simple Coulomb-induced temporal correction to electron trajectories, is proposed to measure the relative time lag of two different ionization events. Using this procedure, the relative lag of polar molecules in two consecutive half laser cycles can be probed with high time resolution.

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Heteronuclear Limit of Strong-Field Ionization: Laser-Induced Fragmentation of HeH⁺

Cited by 3 publications

References 5 publications

Strong-field polarizability-enhanced dissociative ionization

Strong-field polarizability-enhanced dissociative ionization

Post-Ionization Dynamics of the Polar Molecule OCS in Asymmetric Laser Fields

Measuring ionization time lag of polar molecules with a calibrated attoclock

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Heteronuclear Limit of Strong-Field Ionization: Laser-Induced Fragmentation of HeH+

Cited by 3 publications

References 5 publications

Strong-field polarizability-enhanced dissociative ionization

Strong-field polarizability-enhanced dissociative ionization

Post-Ionization Dynamics of the Polar Molecule OCS in Asymmetric Laser Fields

Measuring ionization time lag of polar molecules with a calibrated attoclock

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Heteronuclear Limit of Strong-Field Ionization: Laser-Induced Fragmentation of HeH⁺