81 research outputs found
Hexavalent chromium quantification in solution: Comparing direct UV–visible spectrometry with 1,5-diphenylcarbazide colorimetry
Definition of the stimulated emission threshold in high- nanoscale lasers through phase-space reconstruction
Nanoscale lasers sustain few optical modes so that the fraction of
spontaneous emission funnelled into the useful (lasing) mode is high
(of the order of few 10) and the threshold, which traditionally
corresponds to an abrupt kink in the light in- light out curve, becomes
ill-defined. We propose an alternative definition of the threshold, based on
the dynamical response of the laser, which is valid even for lasers.
The laser dynamics is analyzed through a reconstruction of its phase-space
trajectory for pulsed excitation. Crossing the threshold brings about a change
in the shape of the trajectory and in the area contained in it. An unambiguous
definition of the threshold in terms of this change is shown theoretically and
illustrated experimentally in a photonic crystal laser
Cavity solitons in bidirectional lasers
We show theoretically that a broad area bidirectional laser with slightly
different cavity losses for the two counterpropagating fields sustains cavity
solitons (CSs). These structures are complementary, i.e., there is a bright
(dark) CS in the field with more (less) losses. Interestingly, the CSs can be
written/erased by injecting suitable pulses in any of the two
counterpropagating fields.Comment: 4 figure
Higher-order photon correlations in pulsed photonic crystal nanolasers
We report on the higher-order photon correlations of a high- nanolaser
under pulsed excitation at room temperature. Using a multiplexed four-element
superconducting single photon detector we measured g with
=2,3,4. All orders of correlation display partially chaotic statistics, even
at four times the threshold excitation power. We show that this departure from
coherence and Poisson statistics is due to the quantum fluctuations associated
with the small number of dipoles and photons involved in the lasing process
Diffusion stabilizes cavity solitons in bidirectional lasers
We study the influence of field diffusion on the spatial localized structures
(cavity solitons) recently predicted in bidirectional lasers. We find twofold
positive role of the diffusion: 1) it increases the stability range of the
individual (isolated) solitons; 2) it reduces the long-range interaction
between the cavity solitons. Latter allows the independent manipulation
(writing and erasing) of individual cavity solitons.Comment: submitted to Optics Expres
Vector cavity solitons in broad area Vertical-Cavity Surface-Emitting lasers
We report the experimental observation of two-dimensional vector cavity solitons in a Vertical-Cavity Surface-Emitting Laser (VCSEL) under linearly polarized optical injection when varying optical injection linear polarization direction. The polarization of the cavity soliton is not the one of the optical injection as it acquires a distinct ellipticity. These experimental results are qualitatively reproduced by the spin-flip VCSEL model. Our findings open the road to polarization multiplexing when using cavity solitons in broad-area lasers as pixels in information technology
Regenerative memory in time-delayed neuromorphic photonic resonators
We investigate a photonic regenerative memory based upon a neuromorphic oscillator with a delayed self-feedback (autaptic) connection. We disclose the existence of a unique temporal response characteristic of localized structures enabling an ideal support for bits in an optical buffer memory for storage and reshaping of data information. We link our experimental implementation, based upon a nanoscale nonlinear resonant tunneling diode driving a laser, to the paradigm of neuronal activity, the FitzHugh-Nagumo model with delayed feedback. This proof-of-concept photonic regenerative memory might constitute a building block for a new class of neuron-inspired photonic memories that can handle high bit-rate optical signals
Environmental Electrokinetics for a sustainable subsurface
International audienceSoil and groundwater are key components in the sustainable management of the subsurface environment. Source contamination is one of its main threats and is commonly addressed using established remediation techniques such as in-situ chemical oxidation (ISCO), in-situ chemical reduction (ISCR; most notably using zero-valent iron [ZVI]), enhanced in-situ bioremediation (EISB), phytoremediation, soil-washing, pump-and-treat, soil vapour extraction (SVE), thermal treatment, and excavation and disposal. Decades of field applications have shown that these techniques can successfully treat or control contaminants in higher permeability subsurface materials such as sands, but achieve only limited success at sites where low permeability soils, such as silts and clays, prevail. Electrokinetics (EK), a soil remediation technique mostly recognized in in-situ treatment of low permeability soils, has, for the last decade, been combined with more conventional techniques and can significantly enhance the performance of several of these remediation technologies, including ISCO, ISCR, EISB and phytoremediation. Herein, we discuss the use of emerging EK techniques in tandem with conventional remediation techniques, to achieve improved remediation performance. Furthermore, we highlight new EK applications that may come to play a role in the sustainable treatment of the contaminated subsurface
Spontaneous motion of localized structures and localized patterns induced by delayed feedback
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