Multiple ionization of ions and atoms by intense ultrafast laser pulses

Suresh, M.; McKenna, J.; Srigengan, B.; Williams, Ian D.; English, E. M. L.; Stebbings, Sarah L.; Bryan, William A.; Newell, W R; Divall, E. J.; Hooker, C. J.; Langley, A. J.

doi:10.1016/j.nimb.2005.03.176

Cited by 17 publications

(15 citation statements)

References 3 publications

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“…Hence, for obtaining the same ionisation rate, the intensity and thus electric field of the circularly polarised pulse has to be increased. Theoretical calculations of the TI rate lead to I (lin) = 0.65I (cir) , as the intensity relationship for achieving this [44]. This has been verified experimentally for atoms and small molecules [44,45], including CO 2 [16].…”

Section: Ellipticity Dependencementioning

confidence: 61%

“…However, it has been pointed out in section 2.1.2 that the ionisation yield per pulse in a circularly polarised field is lower than in a linearly polarised one at the same intensity. For achieving the same ionisation rate in atoms and small molecules, the intensity relationship I (lin) = 0.65I (cir) has been verified [16,44,45]. Yet in this experimental setup, significant focal volume averageing is expected, such that one cannot rely on this exact relationship.…”

Section: Experiments 721 Setup and Proceduresmentioning

confidence: 84%

“…The resulting values for ∆A are displayed in table 7.1. The reason for this could be the large focal volume averageing effect that has been avoided in experiments where ionisation rate matching for linear and circular polarisation has been achieved successfully [44,45]. In this section the O + (1,0) channel is discussed.…”

Section: Discussionmentioning

confidence: 99%

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Resolving Strong Field Dynamics in Cation States of CO_2 via Optimised Molecular Alignment

Oppermann

2014

Springer Theses

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In this thesis, the role of the molecular structure in strong field induced processes in CO 2 is resolved by the use of optimised impulsive molecular alignment. Two processes were investigated: recollision induced ionisation and the dissociation of the molecular ion CO + 2 . Both processes are driven by the initial tunneling ionisation of CO 2 . Through the use of molecular alignment, the orbital symmetries of the involved molecular ionic states were resolved, revealing the internal molecular dynamics in the form of ionisation and excitation pathways.A novel data analysis procedure was developed to extract the alignment distribution and rotational temperature of the impulsively aligned molecular ensemble. This facilitated the optimisation of molecular alignment in mixed gas samples and was demonstrated for N 2 , O 2 and CO 2 seeded in Ar.The recollision induced or nonsequential double ionisation (NSDI) of CO 2 was then studied in the molecular frame. The process was fully characterised by measuring the shape of the recolliding electron wavepacket and the angularly resolved inelastic electronion recollision cross section. The results reveal the contribution from both the ionic ground and first excited state of CO + 2 to the NSDI mechanism. This study was extended to the strong field induced dissociation of impulsively aligned CO + 2 . It was found that dissociation is driven by a parallel dipole transition from the second excited ionic state B to the predissociating state C, whilst recollision excitation was shown to not play a role. The strong field induced coupling of the ionic states B and C could thus be controlled by the laser polarisation.The results obtained in this thesis further the understanding of population dynamics of cation states in strong field processes. This is of special interest for extending molecular strong field physics to the study of electronic degrees of freedom and their coupling to the nuclear motion. had hoped for in a research degree and I cannot thank Jon enough for making it such an enriching experience, both professionally and personally.

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Section: Ellipticity Dependencementioning

confidence: 61%

Section: Experiments 721 Setup and Proceduresmentioning

confidence: 84%

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Resolving Strong Field Dynamics in Cation States of CO_2 via Optimised Molecular Alignment

Oppermann

2014

Springer Theses

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“…Similarly, a vast amount of reported study on the effect of polarization on fragmentation shows a substantial suppression of fragmentation channel when polarization is altered from linear to circular for non-resonant dissociation [15][16][17][18][19][20][21][22]. Such suppression with circular polarization has been associated with electron re-scattering or re-collision (ERC) [23] though the molecular fragmentation pattern has been unaffected by laser polarization [24,25].…”

Section: Introductionmentioning

confidence: 98%

Chirp and polarization control of femtosecond molecular fragmentation

2012

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We explore the simultaneous effect of chirp and polarization as the two control parameters for non-resonant photo-dissociation of n-propyl benzene. Experiments performed over a wide range of laser intensities show that these two control knobs behave mutually exclusively. Specifically, for the coherently enhanced fragments (C 3 H 3 + , C 5 H 5 + ) with negatively chirped pulses and C 6 H 5 + with positively chirped pulses, polarization effect is the same as compared to that in the case of transform-limited pulses. Though a change in polarization affects the overall fragmentation efficiency, the fragmentation pattern of n-propyl benzene molecule remains unaffected in contrast to the chirp case.

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“…With circularly polarized pulses, ionized electrons have large transverse momenta and hence a negligible probability of recollision. Thus, inelastic rescattering effects are seen as an enhancement to the linear double ionization signal [12] or, by conservation of flux, a corresponding decrease in the linear single ionization signal [13]. It might be expected that recombination could similarly be observed as a loss of flux in the single ionization linear signal when compared to the corresponding circular signal.…”

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confidence: 99%

Excited Ions in Intense Femtosecond Laser Pulses: Laser-Induced Recombination

et al. 2007

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Electron-ion recombination in a laser-induced electron recollision is of fundamental importance as the underlying mechanism responsible for the generation of high-harmonic radiation and hence for the production of attosecond pulse trains in the extreme ultraviolet and soft x-ray spectral regions. By using an ion beam target, remotely prepared to be partially in long-lived excited states, the recombination process has for the first time been directly observed and studied. DOI: 10.1103/PhysRevLett.99.173002 PACS numbers: 32.80.Rm, 32.80.Wr Intense ultrashort laser pulses are an important tool for probing the nonlinear physics of atoms, molecules and clusters in the inherent strong fields. Such studies have been used to elucidate fundamental quantum processes in the regime where electric (E) field strengths are of a similar order of magnitude to that binding electrons and where pulse time scales approaching a femtosecond constrain the quantum dynamics. In addition some of the resulting processes are being harnessed, for example, high-harmonic generation to produce attosecond x-ray pulses [1] in order to further probe atomic systems [2] and for practical nanotechnological applications [3,4].Arguably the single most important aspect of intense field studies is the ''rescattering'' of an ionized electron from its ionic core in a linearly polarized pulse. Proposed in a seminal paper by Corkum [5], the process relies on the ejected electron periodically revisiting the core as it is driven to and from it by the oscillating E-field of the laser. Acceleration in the external field, coupled with Coulombic acceleration and focussing may lead to recollision with the ion core. The narrow momentum distribution of the wave packet results in a significant probability of electron-ion interaction. This opens up the fascinating prospect of studying electron-ion scattering phenomena, notoriously difficult to investigate in a conventional beam-beam approach [6], with the added bonus that the electron ''pulse'' is on a femtosecond time scale [7].The possible electron collision mechanisms, i.e., elastic scattering, inelastic scattering, and recombination, have all been observed by various means. Elastic scattering leads to momentum transfer, such that the scattered electron is unlikely to further recollide with the core and will be observable at the high energy extreme of the detected electron spectrum, contributing to the above-threshold ionization process [8]. Inelastic scattering contributes to the nonsequential ionization process, either directly by electron impact ionization [9] or indirectly by excitation followed by tunnelling ionization in the field [10]. Recombination, which may be regarded as the inverse of above-threshold ionization, has been observed by detection of the stabilizing photon, the source of high-harmonic generation [11]. However, the underlying effect of laserinduced recombination has not been independently experimentally studied in the femtosecond pulse regime, and indeed recombination has never been detect...

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Multiple ionization of ions and atoms by intense ultrafast laser pulses

Cited by 17 publications

References 3 publications

Resolving Strong Field Dynamics in Cation States of CO_2 via Optimised Molecular Alignment

Resolving Strong Field Dynamics in Cation States of CO_2 via Optimised Molecular Alignment

Chirp and polarization control of femtosecond molecular fragmentation

Excited Ions in Intense Femtosecond Laser Pulses: Laser-Induced Recombination

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