Plasmonic generation of attosecond pulses and attosecond imaging of surface plasmons

Attosecond pulses are ultrashort radiation bursts produced via high
harmonic generation (HHG) during a highly nonlinear excitation
process driven by a near infrared (NIR) laser pulse. Attosecond
pulses can be used to probe the electron dynamics in ultrafast
processes via the attosecond streaking technique, with a resolution
on the attosecond time scale. In this thesis it is shown that both
the generation of attosecond (AS) pulses and the probing of
ultrafast processes by means of AS pulses, can be extended to cases
in which the respective driving and streaking fields are produced
by surface plasmons excited on nanostructures at NIR wavelengths.
Surface plasmons are optical modes generated by collective
oscillations of the surface electrons in resonance with an external
source. In the first part of this thesis, the idea of high harmonic
generation (HHG) in the enhanced field of a surface plasmon is
analyzed in detail by means of numerical simulations. A NIR pulse
is coupled into a surface plasmon propagating in a hollow core
tapered waveguide filled with noble gas. The plasmon field
intensity increases for decreasing waveguide radius, such that at
the apex the field enhancement is sufficient for producing high
harmonic radiation. It is shown that with this setup it is possible
to generate isolated AS pulses with outstanding spatial and
temporal structure, but with an intensity of orders of magnitude
smaller than in standard gas harmonic arrangements. In the second
part, an experimental technique for the imaging of surface
plasmonic excitations on nanostructured surfaces is proposed, where
AS pulses are used to probe the surface field by means of
photoionization. The concept constitutes an extension of the
attosecond streak camera to ``Attosecond Photoscopy'', which allows
space- and time-resolved imaging of the plasmon dynamics during the
excitation process. It is numerically demonstrated that the
relevant parameters of the plasmonic resonance buildup phase can be
determined with subfemtosecond precision. Finally, the method used
for the numerical solution of the Maxwell's equations is discussed,
with particular attention to the problem of absorbing boundary
conditions. New insights into the mathematical formulation of the
absorbing boundary conditions for Maxwell's equations are provided.