A. L'Huillier, J. Mauritsson, P. Johnsson. T. Remetter, E. Gustafsson, T.
Ruchon and M. Swoboda,
Department of Physics, Lund University, P. O. Box 118, SE-221 00
Lund, Sweden
The characteristic plateau region of the harmonic spectrum produced when an
atom is ionized in an intense infrared laser field spans from the
ultraviolet into the soft X-ray region, thus providing enough bandwidth to
produce pulses of hundred attoseconds. However, the different frequency
components in the harmonic spectrum are not naturally
synchronized. Ensuring or imposing a sufficient degree of synchronization
over a certain spectral bandwidth, combined with the filtering of this
bandwidth is the biggest problem that must be overcome for the production
of short attosecond pulses. In this communication, we report on the
different technologies that can be used to spectrally filter and phase
control high-order harmonics in order to produce sub-200 as pulses on
target in a wide energy region [1-4].
Applications of attosecond pulses are emerging. We will present
applications of attosecond pulses to time-resolved studies of ionization of
rare gas atoms by attosecond pulses in presence of an infrared laser pulse
[3-5] and to interferometric measurements of electron wave packets [6]. Our
experiments consist in measuring the angular and energy-resolved electron
emission from atoms exposed to a train of attosecond pulses in presence of
an infrared laser field using a velocity map imaging technique. The
momentum distributions depend on the timing of injection of the electron
wave packets in the continuum relative to the laser cycle. We will
especially discuss the results presented in [6] where the interferences
between wave packets created at a given time in the infrared cycle and
those created half a cycle later are studied as a function of the relative
delay between the infrared field and the attosecond pulses. In some
cases, information on the phase of the electron wave packet can be
extracted from the interferograms, in a way resembling spectral-shearing
interferometry of optical pulses.
[1] R. López-Martens et al, Phys. Rev. Lett. 94, 033001 (2005)
[2] A.-S. Morlens et al., Opt. Lett. 31, 1558 (2006)
[3] P. Johnsson et al., in preparation
[4] J. Mauritsson et al., Phys. Rev. Lett., in press (2006)
[5] P. Johnsson et al., Phys. Rev. Lett. 95, 013001 (2005)
[6] T. Remetter et al, Nature Physics 2, 323 (2006)
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