HAL Portal IOGS (nstitut d'Optique Graduate School)
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Tracking exceptional points above the lasing threshold
No full textInternational audienceRecent studies on exceptional points (EPs) in non-Hermitian optical systems have revealed unique traits, including unidirectional invisibility, chiral mode switching and laser self-termination. In systems featuring gain/loss components, EPs are commonly accessed below the lasing threshold, i.e., in the linear regime. In this work, we experimentally demonstrate that EP singularities in coupled semiconductor nanolasers can be accessed above the lasing threshold, where they become branch points of a nonlinear dynamical system. Contrary to the common belief that unavoidable cavity detuning impedes the formation of EPs, here we demonstrate that such detuning is necessary for compensating the carrier-induced frequency shift, hence restoring the EP. Furthermore, we find that the pump imbalance at lasing EPs varies with the total pump power, enabling their continuous tracking. This work uncovers the unstable nature of EPs above laser threshold in coupled semiconductor lasers, offering promising opportunities for the realization of self-pulsing nanolaser devices and frequency combs
Effets collectifs dans les gaz ultra-froids de potassium 39 habillé par radio-fréquence
No full textJust like Van der Waals gases, quantum gases have some universal thermodynamic properties in deviation to the ideal gas. A dilute quantum fluid of neutral particles has an equation of state involving very few intrinsic parameters. The use of mixtures of two Bose-Einstein condensate allow for the diminution or even cancellation of some terms in the dynamical equation of the fluid. In this context, it was experimentally observed that the physics of an ultra-cold RF-dressed atomic gas (quantum coherent mixture) is much richer than in absence of RF coupling. On the one hand, collective effects usually insignificant - three body elastic interactions - rise and dominate the mean-field properties of the fluid. On the other hand, some beyond-mean field effects - interaction renormalization and quantum vacuum energy - are modified and enhanced. Consequently, We observed novel dynamical properties in potassium 39 RF dressed quantum gases.Tout comme les gaz de Van der Waals, les gaz quantiques ont des propriétés thermodynamiques universelles et proches de celles du gaz parfait. Un fluide quantique dilué de particules neutres a une équation d'état faisant intervenir peu de paramètres intrinsèques. L'utilisation d'un mélange de deux condensats de Bose-Einstein permet de diminuer voire d'annuler complètement certains termes de l'équation dynamique du fluide. Dans ce contexte, il a été observé expérimentalement que la physique d'un gaz atomique habillé par un champ radio-fréquence (mélange quantique) est beaucoup plus riche qu'en l'absence du champ. D'une part, des effets collectifs habituellement négligeables - interactions élastiques à trois corps - apparaissent et deviennent prépondérant dans les propriétés de champ moyen du fluide. D'autre part, des effets au-delà du champ moyen - renormalisation des interactions et énergie quantique de point zéro - sont modifiés et exaltés. En conséquence, nous avons pu observer des propriétés dynamiques nouvelles dans des gaz quantiques de potassium 39 habillés par radio-fréquence
Time-resolved vibrational spectroscopy using Chirped-Pulse Upconversion of mid-infrared pulses generated with a 250-kHz Yb fiber laser by intrapulse difference frequency mixing
No full textInternational audienc
Inverse problem approach for SPHERE+ adaptive optics control
No full textInternational audienceInverse problem approach for SPHERE+ adaptive optics contro
Evaluation of convolutional neural networks as an alternative for the non-linear fitting for multiple exposure speckle imaging of blood flow
No full textInternational audienceWe evaluate in the present study the implementation of a residual convolutional neural network (CNN) to extract blood flow maps based on MESI synthetic exposure data as an alternative to the non-linear fit method. The neural network has been trained on a MESI speckle contrast images database developed using microfluidic channels of various diameter and controlled flows both representative of the physiology of rodents brains
Observation of a non-equilibrium superradiant phase transition in free space
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PANG: Pattern-Based Anomaly Detection in Graphs
No full textPang (Pattern-Based Anomaly Detection in Graphs) is an algorithm which represents and classifies a collection of graphs according to their frequent patterns (subgraphs). The detail of this algorithm are described in the below article. This work was conducted in the framework of the DeCoMaP ANR project (Detection of corruption in public procurement markets -- ANR-19-CE38-0004)