21 May 2009 Mapping of attosecond ionization dynamics by recollision-free higher-order harmonic generation
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In the presence of a high-intensity optical field, electrons are released from atoms on an attosecond time scale. Moreover, in the tunnelling regime, this process displays a strong sensitivity to the carrier-envelope phase (CEP) of a few-cycle light pulse. Tunnelling ionization - a fascinating quantum mechanical phenomenon - leads to a quasi-stepwise increase of free electron density and, as a consequence, of the refractive index of the medium. These steps of the refractive index, corresponding to half-cycles of the driving optical field, impose a transient attosecond phase mask. By scattering probe light off this mask we detect quasi-periodic higher-order harmonics, the spectrum of which, unlike that of the harmonics originating from intrinsic nonlinearity or driven by electron re-collisions, do not depend on the probe intensity and recollision dynamics. The implemented noncollinear pump-probe experimental technique allows optical harmonics generated due to a tunnelling-ionization-induced modulation of the electric current to be spatially separated from the harmonics originating from atomic and ionic nonlinear susceptibilities, enabling background-free time-resolved detection of electron-tunnelling-controlled harmonic spectra and offering an attractive solution for attosecond optical metrology of gases and bulk solids.
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Aart J. Verhoef, Aart J. Verhoef, Alexander Mitrofanov, Alexander Mitrofanov, Evgenii E. Serebryannikov, Evgenii E. Serebryannikov, Daniil V. Kartashov, Daniil V. Kartashov, Aleksei M. Zheltikov, Aleksei M. Zheltikov, Andrius Baltuska, Andrius Baltuska, } "Mapping of attosecond ionization dynamics by recollision-free higher-order harmonic generation", Proc. SPIE 7354, Nonlinear Optics and Applications III, 73540U (21 May 2009); doi: 10.1117/12.823475; https://doi.org/10.1117/12.823475

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