Attosecond transient absorption spectroscopy: Shedding new light on fundamental light-matter interaction |
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| Lukas Gallmann | |
| ETH Zürich | |
| We employed attosecond transient absorption spectroscopy with isolated as well as with trains of attosecond pulses in a dense helium target in the vicinity of its ionization threshold. The experimental two-color IR/XUV pump-probe configuration reveals rather complementary aspects of the interaction of the two pulses with the target atoms. In a first experiment, the attosecond pulse train probes the interference of transiently bound electron wavepackets excited by the XUV but driven by the IR pulse [1]. The observed sub-cycle modulation of the absorption is strongly suppressed when performing the same experiment with isolated attosecond pulses. This provides evidence for the correctness of the electron wavepacket interference picture. In a second experiment using a similar experimental configuration, we probe the off-resonant interaction of the XUV pulse with the helium atoms. We show that the IR pulse interrupts the intrinsic virtual dipole response induced by the XUV [2]. This leads to the manifestation of net gain and absorption features of comparable magnitude in the XUV. The delay between XUV and IR pulse controls the manifestation of either gain or absorption.
[1] M. Holler, F. Schapper, L. Gallmann, U. Keller, Phys. Rev. Lett. 106, 123601 (2011) |