Abstract
We present the first measurement of the attosecond emission generated from underdense plasma produced on a solid target. We generate high-order harmonics of a femtosecond Ti:sapphire laser focused in a weakly ionized underdense chromium plasma. Using the "Reconstruction of Attosecond Beating by Interference of Two-photon Transitions" (RABITT) technique, we show that the 11th to the 19th harmonic orders form in the time domain an attosecond pulse train with each pulse having 300 as duration, which is only 1.05 times the theoretical Fourier transform limit. Measurements reveal a very low positive group delay dispersion of 4200 as2. Beside its fundamental interest, high-order harmonic generation in plasma plumes could thus provide an intense source of attosecond pulses for applications.
Highlights
High-order harmonic generation (HHG) occurs when an intense short laser pulse is focused into a gas of atoms
We present the first measurement of the attosecond emission generated from underdense plasma produced on a solid target
High-order harmonic generation in plasma plumes could provide an intense source of attosecond pulses for applications
Summary
High-order harmonic generation (HHG) occurs when an intense short laser pulse is focused into a gas of atoms It was first shown theoretically [1] and experimentally [2, 3] that the generated radiation consists of pulses with attosecond duration. Aligned linear molecules allow a coherent control of the attosecond emission [11], or a tomographic reconstruction of the radiating orbital [12, 13], but no real improvement in the efficiency Due to their high ionization potentials, singly charged ions are interesting candidates since they can withstand higher laser intensity and can potentially generate both more intense radiation and higher harmonic orders. Note that overdense plasma is able to produce high harmonics but through the collective oscillations of the free electrons; this process has been shown recently to result in a train of attosecond pulses [16]
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