Abstract
Recent progress in sub-laser-cycle gating of high-order harmonic generation promises to push the limits on optical pulse durations below the atomic unit of time, 24 as, which corresponds to a bandwidth broader than 75 eV. However, the available techniques for attosecond pulse measurement are valid only for narrow-bandwidth spectra, due to one of the key approximations made in the phase retrieval. Here we report a new technique for characterizing attosecond pulses, whereby the spectral phase of the attosecond pulse is extracted from the oscillation component with the dressing laser frequency in the photoelectron spectrogram. This technique, termed PROOF (Phase Retrieval by Omega Oscillation Filtering), can be applied to characterizing attosecond pulses with ultrabroad bandwidths.
Highlights
Single isolated attosecond pulses are an exciting new tool for probing electron dynamics in matter
Other methods such as XUV SPIDER have been proposed [4,5], the measurement of isolated attosecond pulses has so far been performed with the attosecond streak camera or attosecond transient recorder technique [6,7], whereby the attosecond XUV pulse is converted into its electron replica through photoemission in atoms
Two-photon transition interference has been used to characterize the average duration of pulses in an attosecond pulse train
Summary
Single isolated attosecond pulses are an exciting new tool for probing electron dynamics in matter. Generation of attosecond pulses with much shorter pulse durations has not been limited by the available bandwidth of the extreme ultraviolet (XUV) light, as continuum spectra supporting pulse durations of 16 as and 45 as have recently been produced using double optical gating (DOG) [2] and polarization gating (PG) [3] Such pulses could not be temporally characterized with current pulse measurement techniques. It assumes that the bandwidth of the attosecond pulse is much smaller than the central energy of the photoelectrons This central momentum approximation is needed to apply the FROG phase retrieval techniques developed for measurement of femtosecond lasers [8], and it poses a limitation on the shortest attosecond pulses that can be characterized at a given center photon energy. For characterizing 25 as pulses centered at 100 eV, the required laser intensity would produce high-energy photoelectrons through multiphoton and field ionization of the target atoms, which would overlap with the attosecond photoelectron spectrum and destroy much of the information encoded in the streaked spectrogram
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