106 research outputs found
Analogue Gravity and ultrashort laser pulse filamentation
Ultrashort laser pulse filaments in dispersive nonlinear Kerr media induce a
moving refractive index perturbation which modifies the space-time geometry as
seen by co-propagating light rays. We study the analogue geometry induced by
the filament and show that one of the most evident features of filamentation,
namely conical emission, may be precisely reconstructed from the geodesics. We
highlight the existence of favorable conditions for the study of analogue black
hole kinematics and Hawking type radiation.Comment: 4 pages, revised versio
Quantum dot opto-mechanics in a fully self-assembled nanowire
We show that fully self-assembled optically-active quantum dots (QDs)
embedded in MBE-grown GaAs/AlGaAs core-shell nanowires (NWs) are coupled to the
NW mechanical motion. Oscillations of the NW modulate the QD emission energy in
a broad range exceeding 14 meV. Furthermore, this opto-mechanical interaction
enables the dynamical tuning of two neighboring QDs into resonance, possibly
allowing for emitter-emitter coupling. Both the QDs and the coupling mechanism
-- material strain -- are intrinsic to the NW structure and do not depend on
any functionalization or external field. Such systems open up the prospect of
using QDs to probe and control the mechanical state of a NW, or conversely of
making a quantum non-demolition readout of a QD state through a position
measurement.Comment: 20 pages, 6 figure
Exciton Footprint of Self-assembled AlGaAs Quantum Dots in Core-Shell Nanowires
Quantum-dot-in-nanowire systems constitute building blocks for advanced
photonics and sensing applications. The electronic symmetry of the emitters
impacts their function capabilities. Here, we study the fine structure of
gallium-rich quantum dots nested in the shell of GaAs-AlGaAs core-shell
nanowires. We used optical spectroscopy to resolve the splitting resulting from
the exchange terms and extract the main parameters of the emitters. Our results
indicate that the quantum dots can host neutral as well as charges excitonic
complexes and that the excitons exhibit a slightly elongated footprint, with
the main axis tilted with respect to the growth axis. GaAs-AlGaAs emitters in a
nanowire are particularly promising for overcoming the limitations set by
strain in other systems, with the benefit of being integrated in a versatile
photonic structure
Efficient generation of isolated attosecond pulses with high beam-quality by two-color Bessel-Gauss beams
The generation of isolated attosecond pulses with high efficiency and high
beam quality is essential for attosec- ond spectroscopy. We numerically
investigate the supercontinuum generation in a neutral rare-gas medium driven
by a two-color Bessel-Gauss beam. The results show that an efficient smooth
supercontinuum in the plateau is obtained after propagation, and the spatial
profile of the generated attosecond pulse is Gaussian-like with the divergence
angle of 0.1 degree in the far field. This bright source with high beam quality
is beneficial for detecting and controlling the microscopic processes on
attosecond time scale.Comment: 3 pages, 3 figure
Generation and control of extreme-blue shifted continuum peaks in optical Kerr media
We demonstrate tunable, extremely blueshifted continuum in \u3bb=1.055 \u3bcm ultrashort laser pulse filamentation in silica. Close to threshold, the continuum appears as a single, isolated blue peak. The spectral position of the two supercontinuum components can be tuned and a regime with encompassing fundamental and second harmonic is possible to achieve. At higher energies, the continuum expands in bandwidth starting from the blue peak. The spectral dynamics and tunability are explained in terms of X-wave generation and intrafilament pulse splitting which may be controlled by modifying the input pulse focusing conditions
Characterization and analysis of InAs/p-Si heterojunction nanowire-based solar cell
The growth of compound semiconductor nanowires on the silicon platform has opened many new perspectives in the area of electronics, optoelectronics and photovoltaics. We have grown a 1 x 1 mm(2) array of InAs nanowires on p-type silicon for the fabrication of a solar cell. Even though the nanowires are spaced by a distance of 800 nm with a 3.3% filling volume, they absorb most of the incoming light resulting in an efficiency of 1.4%. Due to the unfavourable band alignment, carrier separation at the junction is poor. Photocurrent increases sharply at the surrounding edge with the silicon, where the nanowires do not absorb anymore. This is further proof of the enhanced absorption of semiconductors in nanowire form. This work brings further elements in the design of nanowire-based solar cells
Characterization and analysis of InAs/p-Si heterojunction nanowire-based solar cell
The growth of compound semiconductor nanowires on the silicon platform has opened many new perspectives in the area of electronics, optoelectronics and photovoltaics. We have grown a 1 x 1 mm(2) array of InAs nanowires on p-type silicon for the fabrication of a solar cell. Even though the nanowires are spaced by a distance of 800 nm with a 3.3% filling volume, they absorb most of the incoming light resulting in an efficiency of 1.4%. Due to the unfavourable band alignment, carrier separation at the junction is poor. Photocurrent increases sharply at the surrounding edge with the silicon, where the nanowires do not absorb anymore. This is further proof of the enhanced absorption of semiconductors in nanowire form. This work brings further elements in the design of nanowire-based solar cells
Polarization response of nanowires a la carte
Thanks to their special interaction with light, semiconductor nanowires have opened new avenues in photonics, quantum optics and solar energy harvesting. One of the major challenges for their full technological deployment has been their strong polarization dependence in light absorption and emission. In the past, metal nanostructures have been shown to have the ability to modify and enhance the light response of nanoscale objects. Here we demonstrate that a hybrid structure formed by GaAs nanowires with a highly dense array of bow-tie antennas is able to modify the polarization response of a nanowire. As a result, the increase in light absorption for transverse polarized light changes the nanowire polarization response, including the polarization response inversion. This work will open a new path towards the widespread implementation of nanowires applications such as in photodetection, solar energy harvesting and light emission
Suppression of three dimensional twinning for a 100% yield of vertical GaAs nanowires on silicon
Multiple seed formation by three-dimensional twinning at the initial stages of growth explains the manifold of orientations found when self-catalyzed GaAs nanowires grow on silicon. This mechanism can be tuned as a function of the growth conditions by changing the relative size between the GaAs seed and the Ga droplet. We demonstrate how growing under high V/III ratio results in a 100% yield of vertical nanowires on silicon(111). These results open up the avenue towards the efficient integration of III-V nanowire arrays on the silicon platform
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