Temporal Coherence of Ultrashort High-Order Harmonic Pulses

Bellini, Marco; Lyngå, C; Tozzi, A.; Gaarde, M. B.; Hänsch, Theodor W.; L’Huillier, Anne; Wahlström, Claes‐Göran

doi:10.1103/physrevlett.81.297

Cited by 358 publications

(210 citation statements)

References 14 publications

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“…This creates two spatially separated XFID sources which interfere in the far field ( Fig. 3(a)) [18]. Well-contrasted interference fringes were observed on the detector, reflecting the coherent nature of the XFID process.…”

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confidence: 99%

“…We manipulate the emission using a delayed IR pulse and show that all the key features of TRAX experiments can be observed. Since the measurement is not interferometric anymore and is therefore insensitive to the phase of the emission we implement a two-source interferometry scheme [18] to directly measure the XFID phase. The high sensitivity of our background-free technique enables us to use a broad range of gas pressures, revealing a strong influence of collisions in the T-REX signal even at backing pressures as low as a few tens of mbars, in a range where many TRAX measurements were performed.…”

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confidence: 99%

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

et al. 2017

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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 ...

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

et al. 2017

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“…Regarding the dependence of the EUV-phaseamplitude distribution on q for the plateau harmonics, two intensity-dependent quantum interfering electron trajectories, the long (L) and the short (S), with different flight times, contribute. This is due to gradient forces induced by the driving field onto the electron trajectories, primarily to the off-axis and on-axis harmonic emission [29,[31][32][33] with phases φ L q (I ) and φ S q (I ), respectively. In the deep cutoff spectral region the two trajectories degenerate into one with a single phase.…”

Section: Mapping the Electron Wave-packet Interferencesmentioning

confidence: 99%

“…Figure 2(a) shows the profiles of the plateau harmonics on the surface of the focusing mirror. The outer part of the beam contains mainly radiation resulting from the "long" electron trajectories while the inner part by the "short" [31]. The calculated EUV focus images are obtained by the Debye integral [37], after applying the Huygens-Fresnel principle on a spherical mirror with a 10 cm radius of curvature.…”

Section: Mapping the Electron Wave-packet Interferencesmentioning

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Revealing quantum path details in high-field physics

et al. 2014

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The fundamental mechanism underlying harmonic emission in the strong-field regime is governed by tunnel ionization of the atom, followed by the motion of the electron wave packet in the continuum, and finally by its recollision with the atomic core. Due to the quantum nature of the process, the properties of the electron wave packet strongly correlate with those of the emitted radiation. Here, by spatially resolving the interference pattern generated by overlapping the harmonic radiation emitted by different interfering electron quantum paths, we have succeeded in unravelling the intricacies associated with the recollision process. This has been achieved by mapping the spatial extreme-ultraviolet (EUV)-intensity distribution onto a spatial ion distribution, produced in the EUV focal area through the linear and nonlinear processes of atoms. By in situ manipulation of the intensity-dependent motion of the electron wave packets, we have been able to directly measure the difference between the harmonic emission times and electron path lengths resulting from different electron trajectories. Due to the high degree of accuracy that the present approach provides, we have been able to demonstrate the quantum nature of the recollision process. This is done by quantitatively correlating the photoemission time and the electron quantum path-length differences, taking into account the energy-momentum transfer from the driving laser field into the system. This information paves the way for electron-photon correlation studies at the attosecond time scale, while it puts the recollision process from the semiclassical prospective into a full quantum-mechanical context.

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“…H igh-order harmonic generation (HHG) in gases has opened new domains as the extreme ultraviolet (XUV) beams have specific properties 1-3 like short duration down to the attosecond level 4,5 and good spatial coherence 6 . Using high-energy ultrashort laser pulses to generate attosecond pulses in gases is now largely studied as it should provide highenergy attosecond pulses 7 suitable for XUV induced nonlinear processes 8,9 and coherent XUV imaging 10,11 .…”

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Spatio–spectral structures in high-order harmonic beams generated with Terawatt 10-fs pulses

et al. 2014

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A large international effort is nowadays devoted to increase the energy of the extreme ultraviolet pulses by using high-peak power ultrashort fundamental pulses (Terawatt level). Using such fundamental pulses brings specific constraints that need to be addressed. Here we study high-order harmonic generation in gases with 10 fs pulses at Terawatt peak power and demonstrate that extreme ultraviolet beams can be highly structured and complex in various conditions. We use a single-shot spatially resolved spectral detection and demonstrate direct observation of the spatio-temporal coupling occuring in the generating medium. Clear and reproducible complex spatio-spectral structures are observed in the far field. Similar structures are reproduced with simulations and we show that they are intimately associated to the high nonlinearity of high-order harmonic generation. Those findings are of prime importance for the generation of high-energy attosecond pulses and reveal important issues for their applications.

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Temporal Coherence of Ultrashort High-Order Harmonic Pulses

Cited by 358 publications

References 14 publications

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

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

Revealing quantum path details in high-field physics

Spatio–spectral structures in high-order harmonic beams generated with Terawatt 10-fs pulses

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