Attosecond dynamics of nano-localized fields probed by photoelectron spectroscopy

This work focuses on the interaction of few-cycle laser pulses with
nanosystems. Special emphasis is placed on the spatio-temporal
evolution of the induced near-fields. Measurements on
carrier-envelope-phase (CEP) controlled photoemission from isolated
SiO2 nanospheres are taken by single-shot velocity map imaging
(VMI) combined with CEP tagging. The obtained photoelectron spectra
show a pronounced dependence on the CEP and extend to unexpectedly
high energies. Comparison with numerical simulations identify the
additional Coulomb forces of the liberated electron cloud as an
effective additional acceleration mechanism for distinct
trajectories. For larger spheres, an asymmetry in the field
distribution is classically predicted. This asymmetry is also
observed in the photoelectron momentum distributions. The mapping
between position and momentum space in the VMI approach are
investigated by analyzing the correlation of the photoelectron's
birth and detection position. In a second set of experiments,
photoemission at intensities exceeding 10^14 W/cm^2 from isolated
nanospheres of different composition (SiO2, ZrO2, TiO2, Si, Au) is
examined by stereo time-of-flight spectroscopy. It is found that
the measured cutoff energies scale non-linearly with laser
intensity depending on the material properties of the nanosystem. A
trend towards a unified behavior for high intensities is observed
indicating a drastic change in optical properties within the
duration of the few-cycle laser pulse. The charge carrier
generation mechanisms that could lead to such a transient effect
are discussed. For a better understanding of the interaction of
few-cycle fields with nanosystems, a direct access to the temporal
evolution of (plasmonic) near-fields is highly desirable. The
efforts on the realization of nanoplasmonic attosecond streaking
spectroscopy are presented. Numerical simulations are used to
identify the influence of the inhomogeneous near-field
distributions on the streaking process. First experimental results
obtained from Au nanotips show clear streaking features of
sub-micron localized near-fields. The near-field oscillations are
found to be phase offset as compared to reference measurements. The
exact origin of the streaking features of the Au tip and possible
improvements of the experimental approach are discussed.