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要旨:
In this dissertation, experimental studies on the interaction of intense few-cycle
pulses with doped helium nanodroplets are reported. In single-pulse measurements,
the dopant induced ignition of He nanodroplets by 10 fs near-infrared (NIR) pulses
of peak intensities in the range of 1014-1015 Wcm-2 is demonstrated. This results
in the complete ionization of all the 104 He atoms in the droplet triggered by less
than 10 dopant atoms residing at the center. These experimental observations aided
by a theoretical model demonstrate for the first time, a very efficient absorption
and resonant coupling of intense NIR laser fields to cluster nanoplasmas on a 10 fs
timescale. In pump-probe studies performed with two 10 fs pulses, the effects of
doping these large He nanodroplets with few atoms (1....50) on the previously
known nanoplasma resonance due to ionic expansion are investigated. The crucial
roles played by the highly-charged dopant ions at the center and the surrounding
by helium ions on this expansion occurring on sub- or few-picosecond timescales are
studied. This highlights the prominent dynamical role of the fast expanding shells
of He ions, which was not apparent from previous experiments. Hence, the pumpprobe
studies reported in this work call for a revised view of the expansion-induced
resonance in such composite nanoplasmas.
