arXiv subjects

M. Brambilla

Publications and source records attributed to M. Brambilla.

13 recordsLinked to original sources

arXiv2021

Real-time multimode dynamics of terahertz quantum cascade lasers via intracavity self-detection: observation of self mode-locked population pulsations

Mode-locking operation and multimode instabilities in Terahertz (THz) quantum cascade lasers (QCLs) have been intensively investigated during the last decade. These studies have unveiled a rich phenomenology, owing to the unique properties of these lasers, in particular their ultrafast gain medium. Thanks to this, in QCLs a modulation of the intracavity field intensity gives rise to a strong modulation of the population inversion, directly affecting the laser current. In this work we show that this property can be used to study the real-time dynamics of multimode THz QCLs, using a self-detection technique combined with a 60GHz real-time oscilloscope. To demonstrate the potential of this technique we investigate a free-running 4.2THz QCL, and observe a self-starting periodic modulation of the laser current, producing trains of regularly spaced, ~100ps-long pulses. Depending on the drive current we find two regimes of oscillation with dramatically different properties: a first regime at the fundamental repetition rate, characterised by large amplitude and phase noise, with coherence times of a few tens of periods; a much more regular second-harmonic-comb regime, with typical coherence times of ~105 oscillation periods. We interpret these measurements using a set of effective semiconductor Maxwell-Bloch equations that qualitatively reproduce the fundamental features of the laser dynamics, indicating that the observed carrier-density and optical pulses are in antiphase, and appear as a rather shallow modulation on top of a continuous wave background. Thanks to its simplicity and versatility, the demonstrated technique is a powerful tool for the study of ultrafast dynamics in THz QCLs.

physics.optics↗

arXiv2021

Unifying frequency combs in active and passive cavities: Temporal solitons in externally-driven ring lasers

Frequency combs have become a prominent research area in optics. Of particular interest as integrated comb technology are chip-scale sources, such as semiconductor lasers and microresonators, which consist of resonators embedding a nonlinear medium either with or without population inversion. Such active and passive cavities were so far treated distinctly. Here we propose a formal unification by introducing a general equation that describes both types of cavities. The equation also captures the physics of a hybrid device - a semiconductor ring laser with an external optical drive - in which we show the existence of temporal solitons, previously identified only in microresonators, thanks to symmetry breaking and self-localization phenomena typical of spatially-extended dissipative systems.

physics.optics↗

arXiv2019

Extreme events in forced oscillatory media in 0, 1 and 2 dimensions

One of the open questions in the field of optical rogue waves is the relevance of the number of spatial dimensions in which waves propagate. Here we review recent results on extreme events obtained in 0, 1 and 2 spatial dimensions in the specific context of forced oscillatory media. We show that some dynamical scenarii can be relevant from 0 to 2D while others can take place only in sufficiently large number of spatial dimensions.

physics.optics↗

arXiv2018

Architecture of the data aggregation and streaming system for the European Spallation Source neutron instrument suite

The European Spallation Source (ESS) will provide long neutron pulses for experiments on a suite of different instruments. Most of these will perform neutron data acquisition in event mode, i.e. each detected neutron will be characterised by one absolute timestamp and pixel identifier pair. Slow controls metadata from EPICS, such as sample environment measurements and motor positions, will also be timestamped at their source, so that all data and metadata are streamed as a list of events instead of histograms. A flexible data aggregation and streaming system is being developed combining both open source third-party software and in-house development. This is to be used at ESS and other neutron scattering facilities like ISIS and SINQ, replacing legacy solutions by a shared software collection maintained by a cross-facility effort. The architecture of the Apache Kafka-based system, its metadata forwarding and NeXus file writing components are presented, along with test results demonstrating their integration and the scalability in terms of performance.

physics.ins-det↗

arXiv2017

Dynamics of a broad-band Quantum Cascade Laser. From chaos to coherent dynamics and mode-locking

The dynamics of a multimode Quantum Cascade Laser, is studied in a model based on effective semiconductor Maxwell-Bloch equations, encompassing key features for the radiationmedium interaction such as an asymmetric, frequency dependent, gain and refractive index as well as the phase-amplitude coupling provided by the Henry factor. By considering the role of the free spectral range and Henry factor, we develop criteria suitable to identify the conditions which allow to destabilize, close to threshold, the traveling wave emitted by the laser and lead to chaotic or regular multimode dynamics. In the latter case our simulations show that the field oscillations are associated to self-confined structures which travel along the laser cavity, bridging mode-locking and solitary wave propagation. In addition, we show how a RF modulation of the bias current leads to active mode-locking yielding high-contrast, picosecond pulses. Our results compare well with recent experiments on broad-band THz-QCLs and may help understanding the conditions for the generation of ultrashort pulses and comb operation in Mid-IR and THz spectral regions

physics.optics↗

arXiv2016

Phase solitons and domain dynamics in an optically injected semiconductor laser

We analyze experimentally and theoretically the spatio-temporal dynamics of a highly multimode semiconductor laser with coherent optical injection. Due to the particular geometry of the device (a 1~m long ring cavity), the multimode dynamics can be resolved in real time and we observe stable chiral solitons and domain dynamics. The experiment is analyzed in the framework of a set of effective semiconductor Maxwell-Bloch equations. We analyze the stability of stationary solutions and simulate both the complete model and a reduced rate equation model. This allows us to predict domain shrinking and the stability of only one chiral charge that we ascribe to the finite active medium response time.

nlin.PS↗

arXiv2015

Nanoscale displacement sensing based on nonlinear frequency mixing in quantum cascade lasers

We demonstrate a sensor scheme for nanoscale target displacement that relies on a single Quantum Cascade Laser (QCL) subject to optical feedback. The system combines the inherent sensitivity of QCLs to optical re-injection and their ultra-stability in the strong feedback regime where nonlinear frequency mixing phenomena are enhanced. An experimental proof of principle in the micrometer wavelength scale is provided. We perform real-time measurements of displacement with λ/100 resolution by inserting a fast-shifting reference etalon in the external cavity. The resulting signal dynamics at the QCL terminals shows a stroboscopic-like effect that relates the sensor resolution with the reference etalon speed. Intrinsic limits to the measurement algorithm and to the reference speed are discussed, disclosing that nanoscale ranges are attainable.

physics.optics↗

arXiv2014

Observation of electro-activated localized structures in broad area VCSELs

We demonstrate experimentally the electro-activation of a localized optical structure in a coherently driven broad-area vertical-cavity surface-emitting laser (VCSEL) operated below threshold. Control is achieved by electro-optically steering a writing beam through a pre-programmable switch based on a photorefractive funnel waveguide.

physics.optics↗

arXiv2014

High-loop perturbative renormalization constants for Lattice QCD (III): three-loop quark currents for Iwasaki gauge action and n_f=4 Wilson fermions

This is the third of a series of papers on three-loop computation of renormalization constants for Lattice QCD. Our main point of interest are results for the regularization defined by Iwasaki gauge action and n_f=4 Wilson fermions. Our results for quark bilinears renormalized according to the RI'-MOM scheme can be compared to non-perturbative results. The latter are available for Twisted Mass QCD: being defined in the chiral limit, renormalization constants must be the same. We also address more general problems. In particular, we discuss a few methodological issues connected to summing the perturbative series such as the effectiveness of Boosted Perturbation Theory and the disentanglement of irrelevant and finite volume contributions. Discussing these issues we consider ont only the new results of this paper, but also those for the regularization defined by tree-level Symanzik improved gauge action and n_f=2 Wilson fermions, which we presented in a recent paper of ours. We finally comment to which extent the techniques we put at work in the NSPT context can provide a fresher look into the lattice version of the RI'-MOM scheme.

hep-lat↗

arXiv2010

High loop renormalization constants for Wilson fermions/Symanzik improved gauge action

We present the current status of our computation of quark bilinear renormalization constants for Wilson fermions and Symanzik improved gauge action. Computations are performed in Numerical Stochastic Perturbation Theory. Volumes range from 10^4 to 32^4. Renormalization conditions are those of the RI'-MOM scheme, imposed at different values of the physical scale. Having measurements available at several momenta, irrelevant effects are taken into account by means of hypercubic symmetric Taylor expansions. Finite volumes effects are assessed repeating the computations at different lattice sizes. In this way we can extrapolate our results to the continuum limit, in infinite volume.

hep-lat↗

arXiv2010

The Dirac operator spectrum: a perturbative approach

By computing the Dirac operator spectrum by means of Numerical Stochastic Perturbation Theory, we aim at throwing some light on the widely accepted picture for the mechanism which is behind the Bank-Casher relation. The latter relates the chiral condensate to an accumulation of eigenvalues in the low end of the spectrum. This can be in turn ascribed to the usual mechanism of repulsion among eigenvalues which is typical of quantum interactions. First results appear to confirm that NSPT can indeed enable us to inspect a huge reshuffling of eigenvalues due to quantum repulsion.

hep-lat↗

arXiv2007

On Statistical Mechanics Developments of Clan Concept in Multiparticle Production

Clan concept has been introduced in multiparticle dynamics in order to interpret the wide occurrence of negative binomial (NB) regularity in n-charged particle multiplicity distributions (MDs) in various high energy collisions. The centrality of clan concept led to the attempt to justify its occurrence within a statistical model of clan formation and evolution. In this framework all thermodynamical potentials have been explicitly calculated in terms of NB parameters. Interestingly it was found that NB parameter k corresponds to the one particle canonical partition function. The goal of this paper is to explore a possible temperature and volume dependence of parameter k in various classes of events in high energy hadron-hadron collisions. It is shown that the existence of a phase transition at parton level from the ideal clan gas associated to the semihard component with k>1 to the ideal clan gas of the hard component with k<1 implies a discontinuity in the average number of particles at hadron level.

hep-ph↗

arXiv2006

Maps of zeroes of the grand canonical partition function in a statistical model of high energy collisions

Theorems on zeroes of the truncated generating function in the complex plane are reviewed. When examined in the framework of a statistical model of high energy collisions based on the negative binomial (Pascal) multiplicity distribution, these results lead to maps of zeroes of the grand canonical partition function which allow to interpret in a novel way different classes of events in pp collisions at LHC c.m. energies.

hep-ph↗