Publications by Andrea Crottini

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V groove GaAs/AlGaAs quantum wires are investigated by spatially resolved photoluminescence spectroscopy using a low-temperature scanning near- field optical microscope. The spectra along the wires feature several sharp emission lines, which are understood as the emission from exciton states localized in inhomogeneities of the confining potential. It is expected that these exciton states spatially overlap and that their energies are correlated, which leads to level repulsion. The statistical analysis of the

Near-field optical spectroscopy is used to investigate the effects of disorder in the optical processes in semiconductor quantum wires. We observe photoluminescence emissions from extended, delocalized excitons at low temperatures (5 K) and low excitation densities. Combining high spectral and spatial resolution, we isolate homogeneous emission lines from excitons delocalized over distances up to 600 nm in the fundamental state. The energies of the emissions are consistent with different quantum spatial con

An optical device for amplifying or emitting an optical beam of given wavelength comprises an optical source (20) in combination with a primary optical device (10) which is a semiconductor optical amplifier (SOA), a gain-clamped semiconductor optical ampli ...

The optical speed-up at transparency principle has been successfully applied to a gain-clamped semiconductor optical amplifier yielding a remarkable acceleration in the gain recovery of the device as well as to the disappearance of the typical relaxation oscillations stemming from the coupling between the internal lasing mode and the carrier density. A record gain recovery time of 13 ps has been measured with an available gain of still 16 dB. A small-signal analysis of the semiconductor laser amplifier rate

We have directly measured, under operating conditions, the distributions of carrier densities and temperatures in a gain-clamped semiconductor optical amplifier designed for operation at 1.55 mum. As expected, longitudinal spatial hole burning is much smaller than in conventional semiconductor optical amplifiers and the effects of gain clamping are clearly evidenced. The amplifier nevertheless shows a sizeable temperature increase for both the lattice and the carriers at high currents, which are attributed

We report on the experimental observation of excitonic molecules (biexcitons) in high-quality V-shaped quantum wires. By means of spatially resolved near-field photoluminescence spectroscopy, first we unambiguously isolate excitons with a one-dimensional character, and secondly we present the optical transition from 1D biexciton to 1D exciton as a function of excitation power density. The density of these biexcitonic molecules is shown to increase superlinearly compared to the linear variation of exciton de

GaAs/GaAlAs quantum wires grown by modulated flow rate metalorganic chemical vapour deposition were investigated by spatially resolved photoluminescence spectroscopy using a scanning near-field optical microscope. It was found that the wires decompose into a series of regions that emit luminescence of varying intensity. The spectra of these regions feature several narrow emission lines, which means that there is a series of more or less localised exciton states inside each region. It is expected that these

We report the direct observation of one-dimensional (ID) excitonic molecules (biexcitons) in high quality disorder free semiconductor quantum wires. By means of spatially resolved near-field photoluminescence spectroscopy, we detected delocalized 1D excitons through the spatial extension of their homogeneous emission. 1D biexciton transitions are evidenced by their correlation to the 1D excitons as well as their power dependence. The photoluminescence intensity from biexcitons is shown to increase quadratic

We report on a distance control system for low-temperature scanning near-field optical microscopy, based on quartz tuning fork as shear force sensor. By means of a particular tuning fork optical fiber configuration, the sensor is electrically dithered by an applied alternate voltage, without any supplementary driving piezo, as done so far. The sensitivity in the approach direction is 0.2 nm, and quality factors up to 2850 have been reached. No electronic components are needed close to the sensor, allowing t

Andrea Crottini

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Exciton relaxation and level repulsion in GaAs/AlxGa1-xAs quantum wires

Near-field imaging of one-dimensional excitons delocalized over mesoscopic distances

An integrated holding-beam-at-transparency (hbat) configuration for semiconductor optical amplification or emission

Acceleration of a gain-clamped semiconductor optical amplifier by the optical speed-up at transparency scheme

Density clamping and longitudinal spatial hole burning in a gain-clamped semiconductor optical amplifier

Probing excitonic nonlinearities in quantum wires

Level repulsion of localised excitons observed in near-field photoluminescence spectra

One-dimensional biexcitons in a single quantum wire

Ultra stable tuning fork sensor for low-temperature near-field spectroscopy

Probing carrier dynamics in nanostructures by picosecond cathodoluminescence

Disordering of the Ge(001) surface studied by He atom scattering

Step height oscillations during layer-by-layer growth of Pb on Ge(001)

Time-Resolved Cathodoluminescence of InGaAs/AlGaAs Tetrahedral Pyramidal Quantum structures

Low temperature near-field spectroscopy of quantum wires