6 research outputs found
Functional Plasmonic Nanocircuits with Low Insertion and Propagation Losses
We experimentally demonstrate plasmonic
nanocircuits operating
as subdiffraction directional couplers optically excited with high
efficiency from free-space using optical Yagi-Uda style antennas at
λ<sub>0</sub> = 1550 nm. The optical Yagi-Uda style antennas
are designed to feed channel plasmon waveguides with high efficiency
(45% in coupling, 60% total emission), narrow angular directivity
(<40°), and low insertion loss. SPP channel waveguides exhibit
propagation lengths as large as 34 μm with adiabatically tuned
confinement and are integrated with ultracompact (5 × 10 μm<sup>2</sup>), highly dispersive directional couplers, which enable 30
dB discrimination over Δλ = 200 nm with only 0.3 dB device
loss
Mode Switching and Filtering in Nanowire Lasers
Coherent
light sources confining the light below the vacuum wavelength barrier
will drive future concepts of nanosensing, nanospectroscopy, and photonic
circuits. Here, we directly image the angular emission of such a light
source based on single semiconductor nanowire lasers. It is confirmed
that the lasing switches from the fundamental mode in a thin ZnO nanowire
to an admixture of several transverse modes in thicker nanowires approximately
at the multimode cutoff. The mode competition with higher order modes
substantially slows down the laser dynamics. We show that efficient
photonic mode filtering in tapered nanowires selects the desired fundamental
mode for lasing with improved performance including power, efficiency,
and directionality important for an optimal coupling between adjacent
nanophotonic waveguides
Structural and morphological modifications of thermally reduced cerium oxide ultrathin epitaxial films on Pt(111)
The modifications of the stoichiometry, morphology and surface structure of cerium oxide ultrathin films
induced by thermal treatments under vacuum and oxygen partial pressure were studied using in situ X-ray
photoemission spectroscopy, scanning tunnelling microscopy and low energy electron diffraction. The
effect of the film nominal thickness, heating temperature and heating time on the degree of reduction of
the film was investigated. The reduction is more relevant on the film surface, where different ordered
surface structures were observed at different degrees of reduction for very thin films. The obtained results
are discussed taking into account the dimensionality of the oxide and the effects of the proximity of the Pt
substrate. After reduction it was always possible to re-oxidize the films back to their original oxidation
state by thermal treatment under oxygen-rich conditions
On-Demand Coupling of Electrically Generated Excitons with Surface Plasmons via Voltage-Controlled Emission Zone Position
The
ability to confine and manipulate light below the diffraction
limit is a major goal of future multifunctional optoelectronic/plasmonic
systems. Here, we demonstrate the design and realization of a tunable
and localized electrical source of excitons coupled to surface plasmons
based on a polymer light-emitting field-effect transistor (LEFET).
Gold nanorods that are integrated into the channel support localized
surface plasmons and serve as nanoantennas for enhanced electroluminescence.
By precise spatial control of the near-infrared emission zone in the
LEFET via the applied voltages the near-field coupling between electrically
generated excitons and the nanorods can be turned on or off as visualized
by a change of electroluminescence intensity. Numerical calculations
and spectroscopic measurements corroborate significant local electroluminescence
enhancement due to the high local density of photonic states in the
vicinity of the gold nanorods. Importantly, the integration of plasmonic
nanostructures hardly influences the electrical performance of the
LEFETs, thus, highlighting their mutual compatibility in novel active
plasmonic devices
Continuous Wave Nanowire Lasing
Tin-doped cadmium sulfide nanowires
reveal donor–acceptor
pair transitions at low-temperature photoluminescence and furthermore
exhibit ideal resonator morphology appropriate for lasing at continuous
wave pumping. The continuous wave lasing mode is proven by the evolution
of the emitted power and spectrum with increasing pump intensity.
The high temperature stability up to 120 K at given pumping power
is determined by the decreasing optical gain necessary for lasing
in an electron–hole plasma
Unveiling the Role of Electron-Phonon Scattering in Dephasing High-Order Harmonics in Solids
High-order harmonic generation (HHG) in solids is profoundly influenced by the dephasing of the coherent electron-hole motion driven by an external laser field. The exact physical mechanisms underlying this dephasing, crucial for accurately understanding and modelling HHG spectra, have remained elusive and controversial, often regarded more as an empirical observation than a firmly established principle. In this work, we present comprehensive experimental findings on the wavelength-dependency of HHG in both single-atomic-layer and bulk semiconductors. These findings are further corroborated by rigorous numerical simulations, employing ab initio real-time, real-space time-dependent density functional theory and semiconductor Bloch equations. Our experimental observations necessitate the introduction of a novel concept: a momentum-dependent dephasing time in HHG. Through detailed analysis, we pinpoint momentum-dependent electron-phonon scattering as the predominant mechanism driving dephasing. This insight significantly advances the understanding of dephasing phenomena in solids, addressing a long-standing debate in the field. Furthermore, our findings pave the way for a novel, all-optical measurement technique to determine electron-phonon scattering rates and establish fundamental limits to the efficiency of HHG in condensed matter