Revealing molecular structure and dynamics through high-order harmonic generation driven by mid-IR fields

Torres, Ricardo; Siegel, Thomas; Brugnera, Leonardo; Procino, I.; Underwood, Jonathan G.; Altucci, C.; Velotta, R.; Springate, E.; Froud, C. A.; Turcu, I. C. Edmond; Patchkovskii, Serguei; Ivanov, Misha; Smirnova, Olga; Marangos, J. P.

doi:10.1103/physreva.81.051802

Cited by 98 publications

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“…In experiments we demonstrate that this leads to robust control over the trajectory contributions using a drive field from a femtosecond laser composed of the fundamental ω at 800 nm (intensity ∼ 1.2 × 10 14 W cm −2 ) and its weaker orthogonally polarized second harmonic 2ω (intensity ∼ 0.3 × 10 14 W cm −2 ) with the relative phase between the ω and 2ω fields varied simply by tilting a fused silica plate. This is the first demonstration of short and long quantum trajectory control at the single-atom level.High harmonic generation (HHG) has been extensively studied in the last decade as, for instance, a tool to generate attosecond pulses [1] and to measure both fast nuclear dynamics [2] and hole migration in molecular cations [3,4]. Measuring nuclear and electron dynamics from the emitted harmonics is termed HHG spectroscopy and has hitherto concentrated upon isolating the contribution of the electron trajectories that return most quickly to the core [5] (the short trajectories) to provide a well defined temporal mapping for the emission of different frequency harmonics in the spectrum [2].…”

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Trajectory Selection in High Harmonic Generation by Controlling the Phase between Orthogonal Two-Color Fields

et al. 2011

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We demonstrate control of short and long quantum trajectories in high harmonic emission through the use of an orthogonally polarized two color field. By controlling the relative phase φ between the two fields we show via classical and quantum calculations that we can steer the 2-dimensional trajectories to return, or not, to the core and so control the relative strength of the short or long quantum trajectory contribution. In experiments we demonstrate that this leads to robust control over the trajectory contributions using a drive field from a femtosecond laser composed of the fundamental ω at 800 nm (intensity ∼ 1.2 × 10 14 W cm −2 ) and its weaker orthogonally polarized second harmonic 2ω (intensity ∼ 0.3 × 10 14 W cm −2 ) with the relative phase between the ω and 2ω fields varied simply by tilting a fused silica plate. This is the first demonstration of short and long quantum trajectory control at the single-atom level.High harmonic generation (HHG) has been extensively studied in the last decade as, for instance, a tool to generate attosecond pulses [1] and to measure both fast nuclear dynamics [2] and hole migration in molecular cations [3,4]. Measuring nuclear and electron dynamics from the emitted harmonics is termed HHG spectroscopy and has hitherto concentrated upon isolating the contribution of the electron trajectories that return most quickly to the core [5] (the short trajectories) to provide a well defined temporal mapping for the emission of different frequency harmonics in the spectrum [2]. To extend these measurement concepts we would like to harness the second set of quantum trajectories, the long trajectories, which return after a longer time in the continuum and so increase the temporal range available in the measurement. Ideally this should be done without changing any other aspect of the experimental conditions e.g. the intensity. Hitherto long trajectories could only be optimised by adjusting the macroscopic phase-matching, a procedure that inevitably alters the experimental intensity. We demonstrate a simple experimental technique that provides a powerful tool to achieve the direct selection of the quantum trajectories for a single atom without changing the field intensity. We find that the phase between two orthogonally polarized fields at ω and 2ω determines whether the momentum transfer from the 2ω field permits or frustrates the recollision. We observed that the phases of the second harmonic field that optimise the recollision differ by π/2 for the short and long trajectory. This provides robust control over the single atom quantum trajectories and allows to efficiently switch between trajectories, shifting the emission time for some harmonics by more than 0.3 of an optical period.In the simplified picture, commonly applied to describe HHG, an electron is ionised near the peak of the laser electric field and is driven away from its parent ion. When the field changes direction, the electron is driven back and may recombine [5], emitting a photon with fre- quency that is an odd multip...

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Trajectory Selection in High Harmonic Generation by Controlling the Phase between Orthogonal Two-Color Fields

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“…In the past few years, there have been many experimental and theoretical studies on the HHG of CO 2 from many laboratories, using lasers with different wavelengths and intensities, for CO 2 molecules that are randomly distributed or partially aligned. In particular, for CO 2 molecules that are partially aligned along the polarization axis of the probe laser, many experiments have shown that the HHG spectra exhibit minima and the positions of the minima shift with laser intensities [65,178,187]. The shift of the minimum position with laser intensities has been attributed to the interference between the contributions to HHG from the HOMO-2 with the one from the HOMO, despite HOMO-2 lying at 4.4 eV deeper than the HOMO.…”

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confidence: 99%

“…[ 170,187] appear to show a very weak minimum at photon energy near 45 eV. Without more careful study including different intensities and wavelengths, however, this is not conclusive.…”

Section: Single Homo Orbital Contribution At Low Laser Intensitymentioning

confidence: 92%

“…Similar analysis of this type can be found in Refs. [187,188]. The minimum in the HOMO spectra is due to the minimum in the averaged PR transition dipole of HOMO shown in Fig.…”

Section: Hhg Spectra Of Aligned Comentioning

confidence: 99%

“…The angular distributions of the aligned molecules are obtained by solving the TDSE of rotational wave packet (see Appendix B). The degree of alignment is cos 2 θ =0.60 in The minima in the HHG spectra of CO 2 and their dependence on laser intensity have been widely discussed in the literature [65,187]. In Fig.…”

Section: Hhg Spectra Of Aligned Comentioning

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Theory of Nonlinear Propagation of High Harmonics Generated in a Gaseous Medium

Jin

2013

Springer Theses

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In this thesis, we establish the theoretical tools to investigate high-order harmonic generation (HHG) by intense infrared lasers in a gaseous medium. The macroscopic propagation of both the fundamental and the harmonic fields is taken into account by solving Maxwell's wave equations, while the single-atom (or single-molecule) response is obtained by quantitative rescattering theory. The initial spatial mode of the fundamental laser is assumed either a Gaussian or a truncated Bessel beam. On the examples of Ar, N 2 and CO 2 , we demonstrate that the available experimental HHG spectra with isotropic and aligned target media can be accurately reproduced theoretically even though the HHG spectra are sensitive to the experimental conditions. We show that the macroscopic HHG can be expressed as a product of a macroscopic wave packet and a photorecombination cross section, where the former depends on laser and experimental conditions while the latter is the property of the target only. The factorization makes it possible to retrieve the single-atom or single-molecule structure information from experimental HHG spectra. As for the multiple molecular orbital contribution in HHG, it causes the disappearance of the minimum in the HHG spectrum of aligned N 2 with the increase of laser intensity, and the position of minimum in HHG spectrum of aligned CO 2 depending on many factors is also attributed to it, which could explain why the minima observed in different laboratories may differ. For an important application of HHG as ultrashort light source, we show that measured continuous harmonic spectrum of Xe due to the reshaping of the fundamental laser field can be used to produce an isolated attosecond pulse by spectral and spatial filtering in the far field. For on-going application of using HHG to ionize aligned molecules, we present the photoelectron angular distribution from aligned N 2 and CO 2 in the laboratory frame, which can be compared directly with future experiments. demonstrate that the available experimental HHG spectra with isotropic and aligned target media can be accurately reproduced theoretically even though the HHG spectra are sensitive to the experimental conditions. We show that the macroscopic HHG can be expressed as a product of a macroscopic wave packet and a photorecombination cross section, where the former depends on laser and experimental conditions while the latter is the property of the target only. The factorization makes it possible to retrieve the single-atom or single-molecule structure information from experimental HHG spectra. As for the multiple molecular orbital contribution in HHG, it causes the disappearance of the minimum in the HHG spectrum of aligned N 2 with the increase of laser intensity, and the position of minimum in HHG spectrum of aligned CO 2 depending on many factors is also attributed to it, which could explain why the minima observed in different laboratories may differ. For an important application of HHG as ultrashort light source, we show that measured continu...

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Perspektiven für das Verständnis fundamentaler Elektronenkorrelationen durch Attosekundenspektroskopie

Kraus

Wörner

2018

Angewandte Chemie

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Zusammenfassung Molekülorbitale sind ein sehr erfolgreiches Konzept in der Chemie zur Beschreibung der elektronischen Struktur von Molekülen. Diese Beschreibung ist jedoch unzureichend, wenn die Elektronen in Molekülen stark korreliert sind und nicht als unabhängige Teilchen behandelt werden können. Die Auswirkungen solcher Elektronenkorrelationen sind allgegenwärtig in der Spektroskopie innerer Valenzelektronen durch Ultraviolet-und Röntgenstrahlen, ausserdem können Elektronenkorrelationen Ladungswanderungen in Molekülen vorantreiben und sind verantwortlich für viele exotische Eigenschaften stark korrelierter Materialien. Zeitaufgelöste Spektroskopie mit Attosekundenzeitauösung kann im Allgemeinen Elektronendynamik in Echtzeit verfolgen und kann dadurch einen experimentellen Zugang zu Phänomenen erönen, welche durch Elektronenkorrelation vorangetrieben werden. Die Spektroskopie hoher Harmonischer im Speziellen verwendet die präzise zeitabgestimmte Rekollision von laser-beschleunigten Elektronen, um die elektronische Struktur und Dynamik des untersuchten Systems auf einer sub-Femtosekunden Zeitskala zu messen. In diesem Übersichtsartikel diskutieren wir die Möglichkeiten der Spektroskopie hoher Harmonischer, um Elektronendynamik in Molekülen zu verfolgen. Wir besprechen, wie die Spektroskopie hoher Harmonischer auf qualitative und quantitative Weise analysiert werden kann, um die detaillierte Elektronendynamik in Molekülen nach Ionisierung zu verfolgen. Diese Fortschritte machen die Spektroskopie hoher Harmonischer zu einer vielversprechenden Methode, um fundamentale Elektronenkorrelationen aufzudecken und experimentelle Daten zu komplexen Elektronendynamiken bereitzustellen. * peter.kraus@berkeley.edu † hwoerner@ethz.ch; www.atto.ethz.ch 1

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Revealing molecular structure and dynamics through high-order harmonic generation driven by mid-IR fields

Cited by 98 publications

References 27 publications

Trajectory Selection in High Harmonic Generation by Controlling the Phase between Orthogonal Two-Color Fields

Trajectory Selection in High Harmonic Generation by Controlling the Phase between Orthogonal Two-Color Fields

Theory of Nonlinear Propagation of High Harmonics Generated in a Gaseous Medium

Perspektiven für das Verständnis fundamentaler Elektronenkorrelationen durch Attosekundenspektroskopie

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