Ellipticity dependence of 400 nm-driven high harmonic generation

Khan, Sabih D.; Yan, Chao; Möller, Max; Zhao, Kun; Zhao, Baozhen; Chini, Michael; Paulus, G. G.; Chang, Zenghu

doi:10.1063/1.3653277

Cited by 43 publications

(32 citation statements)

References 18 publications

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“…The same dependence on parameters as in the above equation was recently found in the context of HHG [20]. This same dependence on parameters, both in Rydberg states and in HHG, is due to the condition that, in both cases, the initial transverse electron velocity must cancel out the drift due to the vector potential of the field.…”

Section: Derivation Of the Rydberg Yield As A Function Of Ellipticitysupporting

confidence: 76%

Rydberg state creation by tunnel ionization

Landsman

Pfeiffer²,

Hofmann³

et al. 2013

New J. Phys.

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It is well known from numerical and experimental results that the fraction of Rydberg states (excited neutral atoms) created by tunnel ionization declines dramatically with increasing ellipticity of laser light, in a way that is similar to high harmonic generation (HHG). We present a method to analyze this dependence on ellipticity, deriving a probability distribution of Rydberg states that agrees closely with experimental (Nubbemeyer et al 2008 Phys. Rev. Lett. 101 233001) and numerical results. We show using analysis and numerics that most Rydberg electrons are ionized before the peak of the electric field and therefore do not come back to the parent ion. Our work shows, for the first time, the similarities and differences in the process that distinguishes formation of Rydberg electrons from electrons involved in HHG: ionization occurs in a different part of the laser cycle, but the post-ionization dynamics are very similar in both cases, explaining why the same dependence on ellipticity is observed.

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Section: Derivation Of the Rydberg Yield As A Function Of Ellipticitysupporting

confidence: 76%

Rydberg state creation by tunnel ionization

Landsman

Pfeiffer²,

Hofmann³

et al. 2013

New J. Phys.

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“…r þ . The HHG efficiency is maximized for vanishing v y0 [24,25]. If the bound state has spherical symmetry, the amplitude ratio R is fully determined by the return velocity vector, namely, R ¼ jv y ð r Þ=v x ð r Þj.…”

mentioning

confidence: 99%

Determination of Ionization and Tunneling Times in High-Order Harmonic Generation

Zhao

Lein

2013

Phys. Rev. Lett.

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From the numerical solution of the time-dependent Schrödinger equation, we obtain the times of ionization and return of the laser-driven electron in high-order harmonic generation by probing the dynamics with a second harmonic field polarized orthogonal to the fundamental field and observing the harmonic emission in dependence on the two-color delay. Our retrieval method using complex-time evolution gives ionization and return times in excellent agreement with the quantum-orbit model, while a retrieval based on real-time classical dynamics can introduce substantial errors. Because of the imaginary parts, the harmonic signal polarized along the probe field is nonzero for any two-color delay. The tunneling time can be retrieved under an assumption for the return time. DOI: 10.1103/PhysRevLett.111.043901 PACS numbers: 42.65.Ky, 32.80.Rm High-order harmonic generation (HHG) from atoms or molecules exposed to strong laser pulses has been intensively investigated in the past two decades [1,2]. HHG as a highly nonlinear process provides a unique source of coherent extreme ultraviolet radiation in the form of single attosecond pulses or attosecond pulse trains, which paves the way for monitoring and controlling electronic dynamics on the attosecond time scale [3,4]. Because the HHG signal contains information about electronic dynamics and molecular structure, it is also extensively used for highharmonic spectroscopy [5][6][7][8][9][10].The key to understanding HHG is the three-step model [2]: An electron tunnels into the continuum through the potential barrier formed by the atomic potential and the laser field. Then the electron is accelerated as a free particle in the strong oscillating field. Finally, the electron may recollide with the parent ion and recombine to the initial state by emission of an extreme ultraviolet photon. The photon carries away the sum of the binding energy and the electronic kinetic energy acquired in the continuum. Classical electron dynamics in the continuum is sufficient to explain approximately the cutoff in the harmonic spectrum, but the initial tunnel ionization is a quantummechanical process that requires separate treatment. A complete quantum-mechanical description, based on the strong-field approximation, was developed to give a quantitative treatment of HHG [1]. Resulting from this approach is the quantum-orbit (QO) model, where each harmonic emission frequency is attributed to a few dominant quantum trajectories evolving in complex time [11]. The question arises how accurately reality follows these model trajectories, especially since time-resolved highharmonic spectroscopy is based on the knowledge of the electron excursion times. Another question concerns the physical meaning of the imaginary parts.With the development of time-resolved methods operating on the attosecond scale, the precise timing of electron release from an atom has been investigated for various types of ionization processes. As for single-photon ionization, isolated attosecond pulses were applied to set electr...

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“…Development of high-flux attosecond laser pulses for performing nonlinear optics and attosecond pump-attosecond probe experiments has attracted much interest in recent years [1][2][3]. In order to overcome the low conversion efficiency (∼10 −6 ) from the near-infrared (NIR) driving laser to the extreme ultraviolet (XUV) attosecond pulse, various techniques have been attempted, such as loose focusing [4], use of 400 nm driving lasers [3,5], and various quasi-phase-matching (QPM) techniques [6][7][8].…”

mentioning

confidence: 99%

“…In order to overcome the low conversion efficiency (∼10 −6 ) from the near-infrared (NIR) driving laser to the extreme ultraviolet (XUV) attosecond pulse, various techniques have been attempted, such as loose focusing [4], use of 400 nm driving lasers [3,5], and various quasi-phase-matching (QPM) techniques [6][7][8]. However, the highest achievable pulse energies to date have been on tens of microjoule level for attosecond pulse trains [4] and on the few-nanojoule level for isolated attosecond pulses [9].…”

mentioning

confidence: 99%

Mechanism of quasi-phase-matching in a dual-gas multijet array

et al. 2012

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Quasi-phase-matching in a dual gas (Ar-H 2 ) multijet array has recently been demonstrated to be a promising way to enhance the yield of high-order harmonics (HH). Here, we investigate the HH produced individually from these two gases under identical conditions. Our results indicate that the quasi-phase-matching results from the much lower recombination cross section of H 2 as compared to that of Ar in the energy range of interest, rather than from full ionization of H 2 by the driving laser as proposed previously.

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Ellipticity dependence of 400 nm-driven high harmonic generation

Abstract: High-order harmonic generation: A coherent ultrashort emission in the XUV range AIP Conf.

Cited by 43 publications

References 18 publications

Rydberg state creation by tunnel ionization

Rydberg state creation by tunnel ionization

Determination of Ionization and Tunneling Times in High-Order Harmonic Generation

Mechanism of quasi-phase-matching in a dual-gas multijet array

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