Selection of an electron path of high-order harmonic generation in a two-colour femtosecond laser field

Kim, Chul Min; Nam, Chang Hee

doi:10.1088/0953-4075/39/16/005

Cited by 43 publications

(17 citation statements)

References 25 publications

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“…The introduction of a second orthogonally polarized second-harmonic field increased the conversion efficiency of odd harmonics, which has been reported both in gaseous [22] and plasma [23] HHG studies. In the case of a tin plasma, we also observed strong enhancement of the even (16th) harmonic, which was of the same range of intensity as the odd ones [ Fig.…”

Section: Experimental Studiesmentioning

confidence: 62%

Experimental and theoretical studies of two-color-pump resonance-induced enhancement of odd and even harmonics from a tin plasma

et al. 2012

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We study high-order harmonic generation from a laser-produced tin plasma using 780 and 390 nm, 40 fs, 1 kHz pulses. Varying the chirp of the laser radiation, we observe variation of the harmonic frequency and intensity. The enhanced 16th and 17th harmonics are attributed to the influence of the strong ionic transitions of tin. Theoretical calculations of the photoabsorption spectra reveal the decisive role of Sn II and Sn III transitions in the enhancement of single harmonics. Varying the fundamental frequency we study numerically the spectral width where the harmonic is enhanced. We find, both theoretically and experimentally, that this width is wider than the one of the corresponding resonance in the photoabsorption spectrum. The resonance line modification can be explained by the Stark shift of the autoionizing state in the laser field, as well as the photoionization of this state.

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Section: Experimental Studiesmentioning

confidence: 62%

Experimental and theoretical studies of two-color-pump resonance-induced enhancement of odd and even harmonics from a tin plasma

et al. 2012

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“…It has been shown that two orthogonally polarized fields can be successfully used for imaging atomic wavefunctions [8] or the generation of shorter attosecond pulses [9,10]. It has been proposed that by controlling the relative phase of the two pulses, long and short trajectory selection can be achieved [11]. In this paper we report the first experimental demonstration of trajectory selection in HHG using a bi-chromatic driving field.…”

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confidence: 92%

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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“…In recent years, the orthogonally polarized two-color (OTC) laser pulses have captured the attention of the strong-field community due to their broad applications, such as the generating of clean high-harmonic spectrum [7][8][9], the steering of the electrons with subfemtosecond precision [10][11][12], the tomographic reconstruction of molecular orbitals [13,14], and the directional proton emission in dissociation of molecules [15]. More recently, the OTC pulses were used to investigate experimentally atomic double ionization close to the saturation regime of Ne + [16].…”

Section: Introductionmentioning

confidence: 99%

Intensity-dependent two-electron emission dynamics with orthogonally polarized two-color laser fields

Yuan

Xia

et al. 2015

Phys. Rev. A

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In this paper, we explore the intensity-dependent strong-field double ionization of Ne with orthogonally polarized two-color laser pulses consisting of 800-and 400-nm laser fields. The yield of Ne 2+ as a function of the relative phase φ of the two colors experiences a qualitative transition as the laser intensity decreases from the saturation regime to the far-below-saturation regime. In the saturation regime, our simulations well reproduce the recent experimental observations [Phys. Rev. Lett. 112, 193002 (2014)]. Turning to the far-below-saturation regime, however, we find that the observed small knee structure totally disappears and the maximum yield of Ne 2+ is shifted by a π/2 phase. This is explained by the competition between the trajectory concentration effect and the φ-dependent ionization rate of the tunneling electron. The possibility of controlling over the two-electron emission direction along the 400-nm field through the laser intensity is also investigated. We show that the two-electron emission direction can be reversed by changing the laser intensity for some vales of φ, while this fails for some other values of φ.

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Selection of an electron path of high-order harmonic generation in a two-colour femtosecond laser field

Cited by 43 publications

References 25 publications

Experimental and theoretical studies of two-color-pump resonance-induced enhancement of odd and even harmonics from a tin plasma

Experimental and theoretical studies of two-color-pump resonance-induced enhancement of odd and even harmonics from a tin plasma

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

Intensity-dependent two-electron emission dynamics with orthogonally polarized two-color laser fields

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