Shakeup Excitation during Optical Tunnel Ionization

Litvinyuk, Igor; Légaré, François; Dooley, P. W.; Villeneuve, D. M.; Corkum, P. B.; Zanghellini, Jürgen; Pegarkov, A. I.; Fabián, Christian; Brabec, Thomas

doi:10.1103/physrevlett.94.033003

Cited by 62 publications

(43 citation statements)

References 17 publications

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“…In contrast, in the limit of multiphoton or tunneling ionization, characteristic for strong laser fields, the highest occupied molecular orbital (HOMO) is most efficiently ionized, thereby creating ground-state ions that are often stable against dissociation. Hence, the alignment of the molecules [5] prior to ionization has been imperative for gaining access to MFPADs in strong laser fields [6,7]. However, this approach has limitations.…”

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confidence: 99%

Angular Tunneling Ionization Probability of Fixed-in-SpaceH2Molecules in Intense Laser Pulses

et al. 2009

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Angular tunneling ionization probability of fixed-in-space H₂ molecules in intense laser pulsesWe propose a new approach to obtain molecular frame photoelectron angular distributions from molecules ionized by intense laser pulses. With our method we study the angular tunnel ionization probability of H 2 at a wavelength of 800 nm over an intensity range of 2-4:5 Â 10 14 W=cm 2 . We find an anisotropy that is stronger than predicted by any existing model. To explain the observed anisotropy and its strong intensity dependence we develop an analytical model in the framework of the strong-field approximation. It expresses molecular ionization as a product of atomic ionization rate and a Fourier transform of the highest occupied molecular orbital filtered by the strong-field ionization process.

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confidence: 99%

Angular Tunneling Ionization Probability of Fixed-in-SpaceH2Molecules in Intense Laser Pulses

et al. 2009

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“…For molecules, where ionization can occur via multiple pathways 15 , this assumption will not hold. For the present case of a noble gas the energy values for excited states with different principal quantum number are energetically so high above the ground state that ionization into them is negligible.…”

Section: Early Release Of the Second Electronmentioning

confidence: 99%

Timing the release in sequential double ionization

Pfeiffer¹,

Cirelli²,

Smolarski³

et al. 2011

Nature Phys

209

227

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The timing of electron release in strong-field double ionization poses great challenges both for conceptual definition and for conducting experimental measurements. Here we present coincidence momentum measurements of the doubly charged ion and of the two electrons arising from double ionization of argon using elliptically polarized laser pulses. Based on a semi-classical model, the ionization times are calculated from the measured electron momenta across a large intensity range. This paper discusses how this method provides timings on a coarse and on a fine scale, similar to the hour and the minute hand of a clock. We found that the ionization time of the first electron is in good agreement with the simulation, whereas the ionization of the second electron occurs significantly earlier than predicted.A mong all the methods used to measure time, one of the most fundamental is to measure the angle of a rotating hand, such as is done on an analogue watch face. This principle can be employed in strong-field ionization using laser pulses with close-to-circular polarization. In the attoclock the rotating electric field vector is used to deflect photo-ionized electrons, such that the instant of ionization is mapped to the final angle of the momentum, similar to the minute hand of a clock. The attoclock technique is based on the definition of 'time' by 'counting cycles' 1,2 . During one period the watch hand completes one cycle, such that measuring the emission angle of the electron enables us to measure time at a precision well below one optical period 2 . Thus the measurement provides attosecond timing without using an attosecond pulse.Here we use the attoclock to measure the ionization times of the two electrons in the double ionization of argon. As a result of depletion the averaged ionization time of the electrons is shifted towards the beginning of the pulse, thus requiring a multi-cycle measurement. The magnitude of the electron momenta follows the envelope of the laser pulse and gives a coarse timing for the electron release (that is 'the hour hand of the clock'). The emission angle of the electrons subsequently gives the fine timing (that is 'the minute hand of the clock').The result of the attoclock measurements addresses a fundamental question in double ionization: are there electron correlation mechanisms that are not induced by recollision? With linearly polarized fields in strong-field double ionization the dominating ionization mechanism is induced by recollision of the first emitted electron 3,4 . With close-to-circular polarization, however, we can avoid this recollision and therefore investigate a conceptually even simpler process of few-body quantum mechanics.It is impossible, at present, to simulate this process based on the time dependent Schrödinger equation (TDSE) because of exceedingly large computing time requirements 5 . Instead one describes the process usually in terms of simplifying mechanisms, which can be classified as sequential double ionization (SDI) or non-sequential double ionization ...

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“…* markus.kitzler@tuwien.ac.at Furthermore, an intense laser field can also drive the transfer of population to electronically excited states [15][16][17][18][19][20][21] from which ionization can proceed more easily during the subsequent field cycles. Excitation of a molecule or molecular ion can also be induced by electron recollision, a process originally discovered and studied for atoms [22][23][24].…”

Section: Introductionmentioning

confidence: 99%

Role of proton dynamics in efficient photoionization of hydrocarbon molecules

et al. 2014

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We experimentally investigate the ionization mechanism behind the formation of remarkably high charge states observed in the laser-pulse-induced fragmentation of different hydrocarbon molecules by Roither et al. [Phys. Rev. Lett. 106, 163001 (2011)], who suggested enhanced ionization occurring at multiple C-H bonds as the underlying ionization mechanism. Using multiparticle coincidence momentum imaging we measure the yield of multiply charged fragmenting ethylene and acetylene molecules at several intensities and pulse durations ranging from the few-cycle regime to 25 fs. We observe, at constant intensity, a strong increase of the proton energy with increasing laser pulse duration. It is shown that this is caused by a strong increase in the yield of highly charged parent molecular ions with pulse duration. Based on experimental evidence we explain this increase by the necessary population of precursor states in the parent ion that feature fast C-H stretch dynamics to the critical internuclear distance, where efficient ionization via enhanced ionization takes place. For increasing pulse duration these precursor ionic states are more efficiently populated, which leads in turn to a higher enhanced-ionization probability for longer pulses. Our work provides experimental evidence for the existence of a multiple-bond version of enhanced ionization in polyatomic molecules.

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Shakeup Excitation during Optical Tunnel Ionization

Cited by 62 publications

References 17 publications

Angular Tunneling Ionization Probability of Fixed-in-SpaceH2Molecules in Intense Laser Pulses

Angular Tunneling Ionization Probability of Fixed-in-SpaceH2Molecules in Intense Laser Pulses

Timing the release in sequential double ionization

Role of proton dynamics in efficient photoionization of hydrocarbon molecules

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