4 research outputs found
Probing Coherent Surface Plasmon Polariton Propagation Using Ultrabroadband Spectral Interferometry
Surface plasmon polaritons
(SPPs) are short-lived evanescent waves
that can confine light at the surface of metallic nanostructures and
transport energy over mesoscopic distances. They may be used to generate
and process information encoded as optical signals to realize nanometer-scale
and ultrafast all-optical circuitry. The propagation properties of
these SPPs are defined by the geometry and composition of the nanostructure.
Due to their short, femtosecond lifetimes, it has so far proven difficult
to track this propagation in the time domain and to directly study
the effect of the propagation on the shape of a coherent SPP wavepacket.
Here, we introduce an ultrabroadband far-field spectral interferometry
method, allowing for the reconstruction of the plasmonic field in
the time domain, to characterize coherent SPP propagation in metallic
nanostructures. Group velocity and dispersion of SPPs are determined
with high precision in a broad frequency range in the visible and
near-infrared region, and the propagating SPP field is tracked with
high time resolution over distances of tens of micrometers. Our results
shed new light on the interplay between nanostructure geometry and
coherent SPP propagation and hence are important for probing plasmonāmatter
interactions as well as for implementations of ultrafast plasmonic
circuitry
Spotlight on Excitonic Coupling in Polymorphic and Textured Anilino Squaraine Thin Films
Structural
diffraction analysis of an anilino squaraine with <i>branched</i> isobutyl side chains shows crystallization into
two polymorphic structures in the bulk and in spin-casted thin films.
We observe multipeaked and pleochroic absorption spectra being blue-(red)-shifted
for the monoclinic (orthorhombic) polymorph. We understand the packing
as Coulombic molecular H-(J)-aggregates supporting Davydov splitting.
Pictures of projected Davydov components in oriented thin films fit
well to polarization resolved spectro-microscopy and crossed-polarized
light microscopy investigations. By comparison with literature on
anilino squaraines with <i>linear</i> alkyl side chains,
we point out a general trend for steering the thin film excitonic
properties by simple side chain and/or processing condition variation.
Combined with the ability to locally probe the direction of transition
dipole moments, this adds value to the rational design of functional
thin films for optoelectronic applications, especially envisioning
ultrastrong lightāmatter interactions
Suppression of Radiative Damping and Enhancement of Second Harmonic Generation in Bullās Eye Nanoresonators
We report a drastic increase of the
damping time of plasmonic eigenmodes
in resonant bullās eye (BE) nanoresonators to more than 35
fs. This is achieved by tailoring the groove depth of the resonator
and by coupling the confined plasmonic field in the aperture to an
extended resonator mode such that spatial coherence is preserved over
distances of more than 10 Ī¼m. Experimentally, this is demonstrated
by probing the plasmon dynamics at the field level using broadband
spectral interferometry. The nanoresonator allows us to efficiently
concentrate the incident field inside the central aperture of the
BE and to tailor its local optical nonlinearity by varying the aperture
geometry. By replacing the central circular hole with an annular ring
structure, we obtain 50-times higher second harmonic generation efficiency,
allowing us to demonstrate the efficient concentration of long-lived
plasmonic modes inside nanoapertures by interferometric frequency-resolved
autocorrelation. Such a light concentration in a nanoresonator with
high quality factor has high potential for sensing and coherent control
of light-matter interactions on the nanoscale
Toward Plasmonics with Nanometer Precision: Nonlinear Optics of Helium-Ion Milled Gold Nanoantennas
Plasmonic nanoantennas are versatile
tools for coherently controlling
and directing light on the nanoscale. For these antennas, current
fabrication techniques such as electron beam lithography (EBL) or
focused ion beam (FIB) milling with Ga<sup>+</sup>-ions routinely
achieve feature sizes in the 10 nm range. However, they suffer increasingly
from inherent limitations when a precision of single nanometers down
to atomic length scales is required, where exciting quantum mechanical
effects are expected to affect the nanoantenna optics. Here, we demonstrate
that a combined approach of Ga<sup>+</sup>-FIB and milling-based He<sup>+</sup>-ion lithography (HIL) for the fabrication of nanoantennas
offers to readily overcome some of these limitations. Gold bowtie
antennas with 6 nm gap size were fabricated with single-nanometer
accuracy and high reproducibility. Using third harmonic (TH) spectroscopy,
we find a substantial enhancement of the nonlinear emission intensity
of single HIL-antennas compared to those produced by state-of-the-art
gallium-based milling. Moreover, HIL-antennas show a vastly improved
polarization contrast. This superior nonlinear performance of HIL-derived
plasmonic structures is an excellent testimonial to the application
of He<sup>+</sup>-ion beam milling for ultrahigh precision nanofabrication,
which in turn can be viewed as a stepping stone to mastering quantum
optical investigations in the near-field