6 research outputs found
Loading the Antenna Gap with Two-Dimensional Electron Gas Transistors: A Versatile Approach for the Rectification of Free-Space Radiation
Light
conversion into dc current is of paramount interest for a
wide range of upcoming energy applications. Here we integrated dipole
antennas with field-effect transistors based on a two-dimensional
electron gas, with the specific aim of rectifying free-space radiation
exploiting both artificial and natural nonlinearities. In the present
work, resonant conditions of antenna-coupled field-effect rectifiers
have been identified in a terahertz experiment based on the well-established
GaAs transistor technology. Rectification of free-space radiation
has been observed in a broad 0.15–0.40 THz range by implementing
quasi-optical coupling with a substrate lens to an AlGaAs/GaAs heterostructure
transistor into the gap of a cross-dipole antenna. The short- and
the open-circuit resonances have been clearly identified through a
comparison between experimental photocurrent spectra, electromagnetic
simulations, and antenna models. The former depends only on the dipole
antenna geometry, while the latter is determined by the impedance
matching between the antenna and the integrated device and, as such,
can be even tuned to the desired frequency by applying a dc gate bias.
In addition, the high-mobility two-dimensional electron gas supports
plasma wave cavity resonances featuring natural hydrodynamic nonlinearity.
The resonant peaks corresponding to the different rectification mechanisms
have been identified and discussed in terms of simple lumped-element
models. The demonstrated concepts are extrapolated toward infrared
frequencies, where novel application demands and novel two-dimensional
electron gas materials for antenna-coupled rectifiers are emerging
Fractal-Like Plasmonic Metamaterial with a Tailorable Plasma Frequency in the near-Infrared
In
this work, we show that modulating the fractal dimension of
nanoporous gold allows its effective dielectric response to be tailored
over a wide spectral range of infrared wavelengths. In particular,
the plasma edge and effective plasma frequency depend linearly on
the fractal dimension, which can be controlled by varying the pore
and ligament sizes. Importantly, the fractal porous metal exhibits
superior plasmonic properties compared to its bulk counterpart. These
properties, combined with a longer skin depth on the order of 100–200
nm, enables the penetration of optical energy deep into the nanopores
where molecules can be loaded, thus, achieving more effective light–matter
coupling. These findings may open new pathways to engineering the
optical response of fractal-like or self-similar metamaterials without
the need for sophisticated lithographic patterning
Thermoplasmonic Effect of Surface-Enhanced Infrared Absorption in Vertical Nanoantenna Arrays
Thermoplasmonics
is a method for increasing temperature remotely
using focused visible or infrared laser beams interacting with plasmonic
nanoparticles. Here, local heating induced by mid-infrared quantum
cascade laser illumination of vertical gold-coated nanoantenna arrays
embedded into polymer layers is investigated by infrared nanospectroscopy
and electromagnetic/thermal simulations. Nanoscale thermal hotspot
images are obtained by a photothermal scanning probe microscopy technique
with laser illumination wavelength tuned at the different plasmonic
resonances of the arrays. Spectral analysis indicates that both Joule
heating by the metal antennas and surface-enhanced infrared absorption
(SEIRA) by the polymer molecules located in the apical hotspots of
the antennas are responsible for thermoplasmonic resonances, that
is, for strong local temperature increase. At odds with more conventional
planar nanoantennas, the vertical antenna structure enables thermal
decoupling of the hotspot at the antenna apex from the heat sink constituted
by the solid substrate. The temperature increase was evaluated by
quantitative comparison of data obtained with the photothermal expansion
technique to the results of electromagnetic/thermal simulations. In
the case of strong SEIRA by the Cî—»O bond of poly-methylmethacrylate
at 1730 cm<sup>–1</sup>, for focused mid-infrared laser power
of about 20 mW, the evaluated order of magnitude of the nanoscale
temperature increase is of 10 K. This result indicates that temperature
increases of the order of hundreds of K may be attainable with full
mid-infrared laser power tuned at specific molecule vibrational fingerprints
Superconductivity-Induced Transparency in Terahertz Metamaterials
A plasmonic
analogue of electromagnetically induced transparency
is activated and tuned in the terahertz (THz) range in asymmetric
metamaterials fabricated from high critical temperature (<i>T</i><sub>c</sub>) superconductor thin films. The asymmetric design provides
a near-field coupling between a superradiant and a subradiant plasmonic
mode, which has been widely tuned through superconductivity and monitored
by Fourier transform infrared spectroscopy. The sharp transparency
window that appears in the extinction spectrum exhibits a relative
modulation up to 50% activated by temperature change. The interplay
between ohmic and radiative damping, which can be independently tuned
and controlled, allows for engineering the electromagnetically induced
transparency of the metamaterial far beyond the current state-of-the-art,
which relies on standard metals or low-<i>T</i><sub>c</sub> superconductors
Detection of Strong Light–Matter Interaction in a Single Nanocavity with a Thermal Transducer
The
concept of strong light–matter coupling has been demonstrated
in semiconductor structures, and it is poised to revolutionize the
design and implementation of components, including solid state lasers
and detectors. We demonstrate an original nanospectroscopy technique
that permits the study of the light–matter interaction in single
subwavelength-sized nanocavities where far-field spectroscopy is not
possible using conventional techniques. We inserted a thin (∼150
nm) polymer layer with negligible absorption in the mid-infrared range
(5 μm < λ < 12 μm) inside a metal–insulator–metal
resonant cavity, where a photonic mode and the intersubband transition
of a semiconductor quantum well are strongly coupled. The intersubband
transition peaks at λ = 8.3 μm, and the nanocavity is
overall 270 nm thick. Acting as a nonperturbative transducer, the
polymer layer introduces only a limited alteration of the optical
response while allowing to reveal the optical power absorbed inside
the concealed cavity. Spectroscopy of the cavity losses is enabled
by the polymer thermal expansion due to heat dissipation in the active
part of the cavity, and performed using atomic force microscopy (AFM).
This innovative approach allows the typical anticrossing characteristic
of the polaritonic dispersion to be identified in the cavity loss
spectra at the single nanoresonator level. Results also suggest that
near-field coupling of the external drive field to the top metal patch
mediated by a metal-coated AFM probe tip is possible, and it enables
the near-field mapping of the cavity mode symmetry including in the
presence of a strong light–matter interaction
Origin of optical nonlinearity in plasmonic semiconductor nanostructures
The development of nanoscale nonlinear elements in photonic integrated circuits is hindered by the physical limits to the nonlinear optical response of dielectrics, which requires that the interacting waves propagate in transparent volumes for distances much longer than their wavelength. Here we present experimental evidence that optical nonlinearities in doped semiconductors are due to free-electron and their efficiency could exceed by several orders of magnitude that of conventional dielectric nonlinearities. Our experimental findings are supported by comprehensive computational results based on the hydrodynamic modeling, which naturally includes nonlocal effects, of the free-electron dynamics in heavily doped semiconductors. By studying third-harmonic generation from plasmonic nanoantenna arrays made out of heavily n-doped InGaAs with increasing levels of free-carrier density, we discriminate between hydrodynamic and dielectric nonlinearities. As a result, the value of maximum nonlinear efficiency as well as its spectral location can now be controlled by tuning the doping level. Having employed the common material platform InGaAs/InP that supports integrated waveguides, our findings pave the way for future exploitation of plasmonic nonlinearities in all-semiconductor photonic integrated circuits