Gating attosecond pulse train generation using multicolor laser fields

H. -C. Bandulet, D. Comtois, E. Bisson, A. Fleischer, H. Pépin, J. -C. Kieffer, P. B. Corkum, and D. M. Villeneuve

Phys. Rev. A 81, 013803 – Published 5 January 2010

Abstract

The process of high-order harmonic generation leads to the production of a train of attosecond-duration extreme ultraviolet (XUV) pulses, with one pulse emitted per optical half-cycle. For attosecond pump-probe experiments, a single, isolated attosecond pulse is preferable, requiring an almost continuous spectrum. We show experimentally and numerically that the addition of a second laser field, and later a third, at a noncommensurate frequency relative to the driving field can modify the subcycle shape of the electric field, leading to the appearance of additional spectral components between the usual odd harmonics and in some cases a quasicontinuum. We perform a parametric study of the frequency ratio between the two first laser fields, the result of which is in good agreement with theoretical selection rules. We also show numerically that using three laser frequencies from an optical parametric amplifier can achieve a single attosecond pulse from a 24-fs laser pulse.

Received 15 April 2009

DOI:https://doi.org/10.1103/PhysRevA.81.013803

Authors & Affiliations

H. -C. Bandulet¹, D. Comtois¹, E. Bisson¹, A. Fleischer², H. Pépin¹, J. -C. Kieffer¹, P. B. Corkum², and D. M. Villeneuve²

¹Institut National de la Recherche Scientifique, 1650 Boulevard Lionel-Boulet, Varennes, Québec J3X 1S2, Canada
²National Research Council of Canada, 100 Sussex Drive, Ottawa, Ontario K1A 0R6, Canada

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Vol. 81, Iss. 1 — January 2010

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Images

Figure 1
Typical experimental high-order harmonic spectra generated in argon with an OPA wavelength of 1400 nm ( $I \approx 3 \times 10^{14}$ $W / {cm}^{2}$ ) in (a), showing only odd harmonic orders, and with the addition of a weak 800-nm field ( $I \approx 10^{13}$ $W / {cm}^{2}$ ) in (b). (c) Spectra shown in (a)(red or gray line) and (b)(black line) after integration in the vertical direction. $Ω$ and $ω_{1}$ are the XUV and driving frequencies, respectively.Reuse & Permissions
Figure 2
(a) Schematic of the positions of the frequency components predicted by the model of Fleischer and Moiseyev [28]. (b, c) Experimentally recorded XUV spectra from the HHG in argon using two driving frequencies: $ω_{1}$ is the IR driving field ( $I \approx 10^{14} W / {cm}^{2}$ at all wavelengths) and $ω_{2}$ is the weaker 800-nm field ( $I \approx 10^{13} W / {cm}^{2}$ ). Each horizontal line is the spectrum for a particular OPA signal wavelength ( $ω_{1}$ ). Panel (b) has only the OPA wavelength, while panel (c) has both fields simultaneously present. The color (shading) scale is logarithmic in intensity. The lines from the model have been superimposed for $n_{2} = 0$ , $+ 1$ , and $+ 2$ .Reuse & Permissions
Figure 3
HHG spectra produced in krypton by (a) the signal at 1450 nm ( $I \approx 3 \times 10^{14} W / {cm}^{2}$ ), (b) the idler at 1785 nm ( $I \approx 1.5 \times 10^{14} W / {cm}^{2}$ ), (c) the two beams simultaneously present, and then (d) delayed in time by 200 fs. The vertical scales are shown relative to (a). Here, $ω_{2} / ω_{1} = 0.81$ , that is, close to the case where $ω_{2} \to ω_{1}$ for which the model predicts a dense spectrum consisting of many hyper-Raman lines.Reuse & Permissions
Figure 4
HHG spectra generated in krypton by the OPA signal beam at 1325 nm ( $I \approx 3 \times 10^{14} W / {cm}^{2}$ ) in (a). The OPA signal is combined with (b) 20 $μ$ J at 800 nm ( $I \approx 10^{13} W / {cm}^{2}$ ), (c) 100 $μ$ J at 2020 nm ( $I \approx 10^{13} W / {cm}^{2}$ ), and (d) both 800 and 2020 nm. The HHG amplitude is shown relative to (a).Reuse & Permissions
Figure 5
The electric field resulting from the sum of three fields corresponding to 800, 1300, and 2080 nm. The last two wavelengths represent the signal and idler of an OPA pumped by 800 nm. Each field has a Gaussian envelope with an intensity FWHM of 24 fs. The field is now sufficiently aperiodic that a single attosecond pulse will be generated at the peak of the envelope. The dashed line shows (shifted vertically) the predicted XUV intensity as calculated with a time-dependent Schrodinger equation model with a smoothed hydrogen atom potential. Each electric field had an amplitude of 0.02 a.u. The relative phase was such that all three are sines at the peak of the envelope, the optimum condition for generating an isolated pulse. The XUV was filtered for photons greater than 50 eV. Propagation of the fields was not included.Reuse & Permissions

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