High-Harmonic Spectroscopy: From Femtosecond to Attosecond Molecular Dynamics

Wörner, Hans Jakob

doi:10.2533/chimia.2011.299

Cited by 4 publications

(5 citation statements)

References 30 publications

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“…The observed minima spanned the range 51 -78 fs (for harmonics 21 to 13) and are in quantitative agreement with the wave packet calculations discussed above, as shown in Ref. [50]. These minima are thus caused by the increasing internuclear separation of the molecule, where the de Broglie wavelength λ e of the recombining photoelectron fulfills a destructive interference condition with respect to the electron-hole wavefunction of the dissociating molecule.…”

Section: Discussion Of Results On the Photodissociation Of Br 2 Molecsupporting

confidence: 89%

Time-resolved high-harmonic spectroscopy of valence electron dynamics

Kraus

Wörner

2013

Chemical Physics

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Time-Resolved High-Harmonic Spectroscopy (TRHHS) is an emerging technique for probing valence electron dynamics in molecules undergoing photochemical reactions. A general description of the technique including experimental and theoretical aspects is given. The relation of TRHHS to other time-resolved techniques is discussed, with particular emphasis on the specificities of TRHHS. Coherence endows TRHHS with two of its original properties: the interference of excited and unexcited molecules makes it highly sensitive to small excitation fractions and to the phase of photorecombination matrix elements. In addition, the technique is also sensitive to the variation of the vertical ionization potential, providing additional insights into the photochemical dynamics. The principles of the technique are discussed in relation to recent results on the photochemistry of Br 2 and NO 2 , revealing its sensitivity to different aspects of the dynamics, most notably electronic dynamics occurring in non-adiabatic dynamics.

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Section: Discussion Of Results On the Photodissociation Of Br 2 Molecsupporting

confidence: 89%

Time-resolved high-harmonic spectroscopy of valence electron dynamics

Kraus

Wörner

2013

Chemical Physics

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“…This is illustrated through minima in the amplitude of emission observed during the photodissociation of Br 2 that are consistent with destructive quantum interference. [13,22] Moreover, oscillations observed in the diffracted highharmonic yield in the case of NO 2 are consistent with the evolution of the electronic character of the molecular wave packet as it crosses a conical intersection. [15][16][17]23] Second, TRHHS is sensitive to the variation of the vertical ionization potential along the reaction coordinate.…”

Section: Discussionsupporting

confidence: 75%

“…[13] The high-harmonic amplitudes have been shown to provide additional insights into the evolution of the electronic structure as a function of the reaction coordinate, such as harmonic-order dependent minima that probe the internuclear separation of the molecule as it dissociates. [13,22] The high-harmonic phases reveal the fast variation of the vertical ionization potential with internuclear separation and have also been found to be sensitive to the molecular orientation, as revealed by comparing experiments performed with either ing no off-axis spots, t = 0 (panel b), where one observes both wavemixing and diffraction from the transient grating, and finally t > 0 (panel c), where only transient grating diffraction spots are visible.…”

Section: Methodsmentioning

confidence: 95%

Probing Electronic Dynamics during Photochemical Reactions

Tehlar

Kraus

Wörner³

2013

Chimia

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This review discusses a new method for probing the evolution of the valence-electron structure of molecules during chemical reactions. The method relies on the interaction of an intense infrared laser pulse with molecules that results in the emission of attosecond pulses (1 as = 10–18 s) in a process known as high-harmonic generation. Time-resolved high-harmonic spectroscopy measures the phase and amplitude of attosecond pulses emitted from the reacting molecules through interference with the emission from the unexcited molecules. This coherent detection mechanism provides a high sensitivity to small excitation fractions and direct access to both the amplitude and the phase of attosecond pulses, the latter of which is otherwise very difficult to measure. These observables reveal several complementary aspects of excited-state photochemical dynamics such as dissociation, adiabatic wave-packet evolution and conical intersection dynamics.

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“…High-harmonic spectroscopy of condensed matter High-harmonic spectroscopy has been widely used in atomic and molecular systems 97 , but that knowledge cannot be directly implemented in condensed matter systems because underlying microscopic dynamics are different. In solid-state materials, the laser field-driven electrons are in the proximity of the periodic Coulomb potential, so the usual strong-field approximation 98 , which is the foundation of the three-step re-collision model 4,5 , becomes qualitatively invalid.…”

Section: Applications Of Attosecond X-ray Sourcesmentioning

confidence: 99%

Attosecond science based on high harmonic generation from gases and solids

Li¹,

Lu²,

Chew³

et al. 2020

Nat Commun

242

126

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Recent progress in high power ultrafast shortwave and mid-wave infrared lasers has enabled gas-phase high harmonic generation (HHG) in the water window and beyond, as well as the demonstration of HHG in condensed matter. In this Perspective, we discuss the recent advancements and future trends in generating and characterizing soft X-ray pulses from gasphase HHG and extreme ultraviolet (XUV) pulses from solid-state HHG. Then, we discuss their current and potential usage in time-resolved study of electron and nuclear dynamics in atomic, molecular and condensed matters. T abletop attosecond light sources in the soft X-ray (SXR) spectral region based on highharmonic generation are highly desirable in chemical and material sciences since they can spectroscopically identify specific elements, as well as the oxidation states, charge states and even the spin states of those elements 1. One of the important spectral regions is the "water window" (282-533 eV), which covers the atomic K-shell excitation of carbon and oxygen. Although high harmonics in the water window were first generated with Ti:Sapphire lasers centered at 800 nm more than 20 years ago 2,3 , the X-ray photon flux was too low for timeresolved applications. The mechanism of HHG in gases can be explained by the semiclassical three-step model 4-6. When driving laser-field strength reaches~10 8 V m −1 , the bound electron in the atomic gas can tunnel through the Coulomb potential barrier and become a free electron. In the oscillating laser field, the free-electron wave packet may return to its parent ion with the right time of birth. At recombination, the interference between the wave packets of the returning and bound electrons produces an oscillating dipole that emits attosecond radiation. Returning electrons with various kinetic energy will recombine at different times giving rise to the chirp in the attosecond radiation 7. This process repeats twice for every optical cycle. The temporal beating of attosecond pulses results in the high-harmonic combs in the spectral domain. Empowered by the advances in driving lasers with center wavelengths around 1.8 μm, soft X-ray high harmonics can be generated with a moderate intensity of 10 14 W cm −2 (see Box 1 for details). Significant progress has recently been made in developing attosecond light within the water window 8. By spectrally broadening pulses from an Optical Parametric Amplifier (OPA) using a gas-filled hollow-core fiber 9 or by broadband phase matching in an Optical Parametric Chirped Pulse Amplifier (OPCPA) 10 , two-cycle, mJ-level pulses centered with 1 kHz repetition

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High-Harmonic Spectroscopy: From Femtosecond to Attosecond Molecular Dynamics

Cited by 4 publications

References 30 publications

Time-resolved high-harmonic spectroscopy of valence electron dynamics

Time-resolved high-harmonic spectroscopy of valence electron dynamics

Probing Electronic Dynamics during Photochemical Reactions

Attosecond science based on high harmonic generation from gases and solids

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