Probing the tunnelling site of electrons in strong field enhanced ionization of molecules

Wu, Jian; Meckel, M.; Schmidt, L. Ph. H.; Kunitski, Maksim; Voss, S.; Sann, H.; Kim, H.; Jahnke, T.; Czasch, A.; Dørner, R.

doi:10.1038/ncomms2130

Cited by 98 publications

(101 citation statements)

References 32 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…We use the rotating electric-field vector of the laser pulse as ultrafast clockwork and measure the asymptotic emission direction f el of the tunnelionized electron. The value of f el between 0 and 2p provides the laser phase, relative to an arbitrary reference axis in the laboratory frame, at the ionization instant t i [10][11][12][13][14][15] . However, it is not f el, but rather f el mol , the phase of the laser field relative to the molecular axis at time t i , which determines the degree of anisotropy in bond breaking.…”

Section: Resultsmentioning

confidence: 99%

“…The first technique combines a single attosecond pulse with an intense near-infrared laser pulse, such that the attosecond pulse acts as a start and the phase-locked infrared pulse streaks a freed electron in energy [6][7][8][9] . The second technique, termed 'attosecond angular streaking', uses elliptically polarized light [10][11][12][13][14][15] and adopts either the major axis of the elliptical field or the carrier-envelope phase (CEP) of a CEP-stabilized pulse to provide a reference time. A released electron is then driven to a certain direction by the rotating electric field, which maps the ionization instant within one laser cycle (T p B2.6 fs at 790 nm) to the 2p interval of electron emission directions (B7.3 attosecond for 1°) in the polarization plane.…”

mentioning

confidence: 99%

See 1 more Smart Citation

Understanding the role of phase in chemical bond breaking with coincidence angular streaking

Magrakvelidze

Schmidt

et al. 2013

Nat Commun

Self Cite

View full text Add to dashboard Cite

Electron motion in chemical bonds occurs on an attosecond timescale. This ultrafast motion can be driven by strong laser fields. Ultrashort asymmetric laser pulses are known to direct electrons to a certain direction. But do symmetric laser pulses destroy symmetry in breaking chemical bonds? Here we answer this question in the affirmative by employing a two-particle coincidence technique to investigate the ionization and fragmentation of H 2 by a long circularly polarized multicycle femtosecond laser pulse. Angular streaking and the coincidence detection of electrons and ions are employed to recover the phase of the electric field, at the instant of ionization and in the molecular frame, revealing a phase-dependent anisotropy in the angular distribution of H þ fragments. Our results show that electron localization and asymmetrical breaking of molecular bonds are ubiquitous, even in symmetric laser pulses. The technique we describe is robust and provides a powerful tool for ultrafast science.

show abstract

Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

Understanding the role of phase in chemical bond breaking with coincidence angular streaking

Magrakvelidze

Schmidt

et al. 2013

Nat Commun

Self Cite

View full text Add to dashboard Cite

show abstract

“…The observed forwardbackward dissociation asymmetries imply that the electron is preferentially emitted from the down-field site, in contradiction with the DIU physical picture. Recently, a single-color elliptically polarized laser pulse is used to probe the tunnelling site of electrons from the dimer ArXe by angular streaking technique [23,24]. Wu et al reported that the ionization more easily happens at the up-field site, supporting the DIU physical picture.…”

mentioning

confidence: 82%

“…Wu et al reported that the ionization more easily happens at the up-field site, supporting the DIU physical picture. Because the intuitive physical picture is based on the quasi-static theory, lacking a perspective on the dynamics of ionization processes, controversy still exists in these experiments.To understand the long-standing issues about EI [22,23,[25][26][27], in this Letter, we investigate the electron dynamics and the tunnelling site by carefully examining time evolution of the electron density and ionization rate with numerically solving time-dependent Schrödinger equation (TDSE). A more comprehensive physical picture is established for EI dynamics of diatomic molecules.…”

mentioning

confidence: 99%

Tunneling site of electrons in strong-field-enhanced ionization of molecules

et al. 2014

View full text Add to dashboard Cite

We investigated electron emissions in strong field enhanced ionization of asymmetric diatomic molecules by quantum calculations. It is demonstrated that the widely-used intuitive physical picture, i.e., electron wave packet direct ionization from the up-field site (DIU), is incomplete. Besides DIU, we find another two new ionization channels, the field-induced excitation with subsequent ionization from the down-field site (ESID), and the up-field site (ESIU). The contributions from these channels depend on the molecular asymmetry and internuclear distance. Our work provides a more comprehensive physical picture for the long-standing issue about enhanced ionization of diatomic molecules.PACS numbers: 32.80. Rm, 31.90.+s, 32.80.Fb Tunnelling ionization is one of the most fundamental quantum effects when atoms and molecules are exposed to strong laser field. As the doorway step of various strong-field processes, such as, high-order harmonic and attosecond pulse generation [1,2], double ionization [3,4] and high-order above-threshold ionization [5,6], understanding the ionization dynamics is of essential importance for controlling the electron dynamics in these processes. Moreover, molecular ionization signal itself also preserves some information of the molecular structure, and thus can be used to image molecular structure [7,8]. Therefore, the ionization has attracted significant interests over the past several decades. Theories, including PPT [9], ADK [10], have been well established for atoms. Lots of efforts have also been made to extend these theories to molecules [11]. Nevertheless, because the molecules have more degrees of freedom and more complicated structure, the underlying physics becomes richer and the ionization dynamics is still not completely clear yet. It has been demonstrated that when the molecule is stretched to a critical internuclear distance R c the ionization probability sharply increases, which is called enhanced ionization (EI) [12][13][14][15][16][17][18][19]. An intuitive physical picture [12][13][14] based on the quasi-static tunneling theory [20] have been proposed to explain the behavior of molecular EI. When the molecular is stretched to the critical distance R c , an inner potential barrier between the two cores emerges and localizes the electron population at each of cores. Then, the up-field population only needs to tunnel through the inner barrier directly to the continuum, which is considerably easier than tunnelling through the outer barrier between the down-field core and the continuum. Thus a remarkable enhancement of the ionization probability happens around the critical distance R c . According to the intu- * Corresponding author: pengfeilan@hust.edu.cn † Corresponding author: lupeixiang@mail.hust.edu.cn itive physical picture, electron wave packet direct ionization from the up-field site (DIU) is considered responsible for molecular EI. Although such a DIU physical picture has been commonly used to analyze and explain the experiments of molecular ionization and related ...

show abstract

“…Our work clarifies the long-standing controversy and strengthens the theoretical basis of molecular orbital tomography. The fast development of strong-field physics has provided versatile perspectives for probing the structure and ultrafast electron dynamics in atoms and molecules with attosecond andÅngstörm resolutions [1][2][3][4][5]. A fascinating application, known as molecular orbital tomography (MOT) based on high-order harmonic generation (HHG), has attracted a great deal of attention for its potential use of observing chemical reactions in molecules by directly imaging the valence molecular orbital [6][7][8][9][10][11][12][13][14].…”

mentioning

confidence: 99%

Molecular-orbital tomography beyond the plane-wave approximation

Xiao

Lan

et al. 2014

Phys. Rev. A

View full text Add to dashboard Cite

The use of plane wave approximation in molecular orbital tomography via high-order harmonic generation has been questioned since it was proposed, owing to the fact that it ignores the essential property of the continuum wave function. To address this problem, we develop a theory to retrieve the valence molecular orbital directly utilizing molecular continuum wave function which takes into account the influence of the parent ion field on the continuum electrons. By transforming this wave function into momentum space, we show that the mapping from the relevant molecular orbital to the high-order harmonic spectra is still invertible. As an example, the highest orbital of N2 is successfully reconstructed and it shows good agreement with the ab initio orbital. Our work clarifies the long-standing controversy and strengthens the theoretical basis of molecular orbital tomography. The fast development of strong-field physics has provided versatile perspectives for probing the structure and ultrafast electron dynamics in atoms and molecules with attosecond andÅngstörm resolutions [1][2][3][4][5]. A fascinating application, known as molecular orbital tomography (MOT) based on high-order harmonic generation (HHG), has attracted a great deal of attention for its potential use of observing chemical reactions in molecules by directly imaging the valence molecular orbital [6][7][8][9][10][11][12][13][14]. Following the pioneering work by Itatani et al.[6] which successfully reconstructed the highest occupied molecular orbital (HOMO) of N 2 using high-order harmonic spectra from aligned molecules, MOT has been extended to more complex species such as CO 2 [10] and asymmetric molecules of HeH 2+ [11] and CO [12,13]. The original MOT theory is based on the plane wave approximation (PWA), which assumes that the continuum wave functions are unperturbed by the electron interaction with the parent ion and can be viewed as plane waves [6]. With this assumption, the transition dipole is given in the form of the Fourier transform of the HOMO weighted by the dipole operator. Thus by performing inverse Fourier transform, the HOMO of the molecule can be reconstructed. However, it is a drastic simplification to represent continuum wave functions of a molecule by plane waves, especially in the low-energy region where most HHG experiments are performed. Many effects during the rescattering process in HHG are not treated properly such as the distortion of the continuum wave function due to the molecular potential. Recent works demonstrated that HHG from molecules was influenced by the Coulomb potential of the parent ion and some features of high-order harmonics are attributable to the distortion of continuum wave function [15][16][17]. Thereby, * pengfeilan@hust.edu.cn † lupeixiang@hust.edu.cn the tomographical image of the molecular orbital can be greatly modulated. All these features make the foundation of original MOT procedure unstable. For this reason, the theoretical foundation of MOT has been questioned [18][19][20] since it was propose...

show abstract

Probing the tunnelling site of electrons in strong field enhanced ionization of molecules

Cited by 98 publications

References 32 publications

Understanding the role of phase in chemical bond breaking with coincidence angular streaking

Understanding the role of phase in chemical bond breaking with coincidence angular streaking

Tunneling site of electrons in strong-field-enhanced ionization of molecules

Molecular-orbital tomography beyond the plane-wave approximation

Contact Info

Product

Resources

About