Role of Excited States In High-order Harmonic Generation

Beaulieu, Samuel; Camp, Seth; Descamps, D.; Comby, Antoine; Wanie, Vincent; Petit, S.; Légaré, François; Schafer, K. J.; Gaarde, Mette B.; Catoire, F.; Mairesse, Y.

doi:10.1103/physrevlett.117.203001

Cited by 75 publications

(66 citation statements)

References 30 publications

(35 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In that case, HHG is associated with a channel in which electrons are ionized from an excited state and recombine to the ground state. Recently, this channel was observed experimentally in studies of HHG in argon atoms [9]. In many cases the enhancement is only observed over a narrow band of harmonics [10,11].…”

Section: Introductionmentioning

confidence: 94%

High-order harmonic generation from highly excited states in acetylene

Mulholland

Dundas

2018

Phys. Rev. A

View full text Add to dashboard Cite

High-order harmonic generation (HHG) from aligned acetylene molecules interacting with mid infra-red (IR), linearly polarized laser pulses is studied theoretically using a mixed quantum-classical approach in which the electrons are described using time-dependent density functional theory while the ions are treated classically. We find that for molecules aligned perpendicular to the laser polarization axis, HHG arises from the highestoccupied molecular orbital (HOMO) while for molecules aligned along the laser polarization axis, HHG is dominated by the HOMO-1. In the parallel orientation we observe a double plateau with an inner plateau that is produced by ionization from and recombination back to an autoionizing state. Two pieces of evidence support this idea. Firstly, by choosing a suitably tuned vacuum ultraviolet pump pulse that directly excites the autoionizing state we observe a dramatic enhancement of all harmonics in the inner plateau. Secondly, in certain circumstances, the position of the inner plateau cut-off does not agree with the classical three-step model. We show that this discrepancy can be understood in terms of a minimum in the dipole recombination matrix element from the continuum to the autoionizing state. As far as we are aware, this represents the first observation of harmonic enhancement over a wide range of frequencies arising from autoionizing states in molecules.

show abstract

Section: Introductionmentioning

confidence: 94%

High-order harmonic generation from highly excited states in acetylene

Mulholland

Dundas

2018

Phys. Rev. A

View full text Add to dashboard Cite

show abstract

“…We excite a bound electronic wavepacket in argon atoms by absorption of 5 visible (VIS) photons, which then emits XFID radiation [17]. The spectrum of the exciting light does not overlap anymore with that of the emitted radiation.…”

mentioning

confidence: 99%

Phase-resolved two-dimensional spectroscopy of electronic wave packets by laser-induced XUV free induction decay

et al. 2017

Self Cite

View full text Add to dashboard Cite

We present a novel time-and phase-resolved, background-free scheme to study the extreme ultraviolet dipole emission of a bound electronic wavepacket, without the use of any extreme ultraviolet exciting pulse. Using multiphoton transitions, we populate a superposition of quantum states which coherently emit extreme ultraviolet radiation through free induction decay. This emission is probed and controlled, both in amplitude and phase, by a time-delayed infrared femtosecond pulse. We directly measure the laser-induced dephasing of the emission by using a simple heterodyne detection scheme based on two-source interferometry. This technique provides rich information about the interplay between the laser field and the Coulombic potential on the excited electron dynamics. Its background-free nature enables us to use a large range of gas pressures and to reveal the influence of collisions in the relaxation process.Transient Absorption Spectroscopy (TAS) in the extreme ultraviolet (XUV) range is a powerful technique for ultrafast dynamical studies, from the gas phase [1][2][3] to the solid state [4,5]. The recent progress of attosecond science has made the extension of TAS to the attosecond regime (ATAS) a reality. In the past few years, different configurations of ATAS experiments have emerged. In the first and most intuitive scheme, the XUV attosecond pulses probe a sample that has been pre-excited by an infrared (IR) pump laser pulse. This scheme was for instance used to follow the ultrafast coherent hole dynamics initiated in strong-field ionized krypton [1]. In the second arrangement, the XUV and IR pulses are temporally overlapped. The XUV absorption thus probes the IR-dressed atomic or molecular states, allowing the observation of light-induced states [6,7] as well as sub-cycle AC-Stark-shifts [8]. Finally, in what turned out to be the most widely used scheme, the XUV pulse comes first and serves as a pump, exciting a broadband superposition of quantum states through single-photon absorption. The wavepacket relaxes by coherently emitting XUV radiation (called XUV Free Induction Decay, XFID) that interferes with the incident light. A delayed IR laser field is used to follow or control the relaxation dynamics, such that these experiments can be seen as Transient Reshaping of the Absorption spectrum of the XUV light (TRAX) [9,10].In TRAX experiments, the delayed IR laser pulse has three main effects on the XFID emission ( Fig. 1) : (i) Damping of the emission by ionization of the excited states. This effect induces a lowering and a spectral broadening of the absorption features [2]. (ii) Field coupling of different electronic states, leading to population transfers. The resulting amplitude reshaping of the electronic wavepacket can be detected through temporal beatings in the absorption signal, as demonstrated in atoms [9,10] and molecules [11,12]. (iii) Phase shift induced by the Stark-shift of the excited states. This laser-induced phase was shown to enable full control over the absorption lineshapes, from Lorentz ...

show abstract

“…This would suggest that the first excited ( 2 S e ) state of Ar + may not be optimal for realising resonantly enhanced, multiphoton ionization yields in XIHHG schemes, or of driving HHG from an excited state. In connection with the latter, alternative strategies based on XUV free-induction decay [38][39][40], or direct ionization from an excited state followed by recombination to the ground state [38], offer considerable promise.…”

Section: Cooper Minimummentioning

confidence: 99%

“…It has been demonstrated, for instance, that if the system is prepared in a coherent superposition of different bound states [33][34][35], in which ionization proceeds primarily from the most weakly bound, the harmonic spectrum can present two distinct plateaus, with different conversion efficiencies [36,37]. More recently, HHG from excited states was addressed experimentally, exploiting the attosecond lighthouse effect [38]. There, it was shown that population of high-lying Rydberg states can lead to either XUV freeinduction decay [39,40], or near-threshold ionization followed by recombination to the ground state.…”

Section: Introductionmentioning

confidence: 99%

Extreme-ultraviolet-initiated high-order harmonic generation in Ar+

2018

View full text Add to dashboard Cite

We employ the R-matrix with time-dependence method to investigate extreme-ultravioletinitiated high-harmonic generation (XIHHG) in Ar + . Using a combination of extreme-ultraviolet (XUV, 92 nm, 3 × 10 12 Wcm −2 ) and time-delayed, infrared (IR, 800 nm, 3 × 10 14 Wcm −2 ) laser pulses, we demonstrate that control over both the mechanism, and timing, of ionization can afford significant enhancements in the yield of plateau, and sub-threshold, harmonics alike. The presence of the XUV pulse is also shown to alter the relative contribution of different electron emission pathways. Manifestation of the Ar + electronic structure is found in the appearance of a pronounced Cooper minimum. Interferences amongst the outer-valence 3p, and inner-valence 3s, electrons are found to incur only a minor suppression of the harmonic intensities, at least for the present combination of XUV and IR laser light. Additionally, the dependence of the XIHHG efficiency on time delay is discussed, and rationalized with the aid of classical trajectory simulations.

show abstract

Role of Excited States In High-order Harmonic Generation

Cited by 75 publications

References 30 publications

High-order harmonic generation from highly excited states in acetylene

High-order harmonic generation from highly excited states in acetylene

Phase-resolved two-dimensional spectroscopy of electronic wave packets by laser-induced XUV free induction decay

Extreme-ultraviolet-initiated high-order harmonic generation in Ar+

Contact Info

Product

Resources

About