Probing electronic decoherence with high-resolution attosecond photoelectron interferometry

Quantum coherence plays a fundamental role in the study and control of ultrafast dynamics in matter. In the case of photoionization, entanglement of the photoelectron with the ion is a well known source of decoherence when only one of the particles is measured. Here we investigate decoherence due to entanglement of the radial and angular degrees of freedom of the photoelectron. We study two-photon ionization via the 2s2p autoionizing state in He using high spectral resolution photoelectron interferometry. Combining experiment and theory, we show that the strong dipole coupling of the 2s2p and 2p$^2$ states results in the entanglement of the angular and radial degrees of freedom. This translates, in angle integrated measurements, into a dynamic loss of coherence during autoionization

Ultralight vector dark matter search using data from the KAGRA O3GK run

Among the various candidates for dark matter (DM), ultralight vector DM can be probed by laser interferometric gravitational wave detectors through the measurement of oscillating length changes in the arm cavities. In this context, KAGRA has a unique feature due to differing compositions of its mirrors, enhancing the signal of vector DM in the length change in the auxiliary channels. Here we present the result of a search for U(1)B−L gauge boson DM using the KAGRA data from auxiliary length channels during the first joint observation run together with GEO600. By applying our search pipeline, which takes into account the stochastic nature of ultralight DM, upper bounds on the coupling strength between the U(1)B−L gauge boson and ordinary matter are obtained for a range of DM masses. While our constraints are less stringent than those derived from previous experiments, this study demonstrates the applicability of our method to the lower-mass vector DM search, which is made difficult in this measurement by the short observation time compared to the auto-correlation time scale of DM

Excitability and laser localized structures in semiconductor microcavities

Excitabilité et structures localisées sont des phénomènes universels qui ont été observés dans une grande variété de systèmes. Chacun des deux phénomènes a des propriétés intéressante pour des applications potentielles, surtout dans l'optique. L'excitabilité est la propriété intrinsèque du neurone, elle décrit sa réponse à une stimulation: pour des stimulations en-dessous d'un certain seuil, le neurone reste dans son état de repos mais quand la stimulation dépasse ce seuil, il émet une impulsion dont la taille ne dépend pas de la force de la stimulation. Les structures localisées dans les systèmes optiques sont des pics de surintensité qui coexistent avec un fond homogène sur la section transversale spatialement étendue d'une cavité laser. Dans cette thèse nous avons étudié l'apparition de ces deux phénomènes non-linéaires dans des microcavités à semi-conducteur, pour lesquelles les applications dans le traitement tout-optique de l'information sont prometteuse. En outre, nous avons étudié la possibilité de trouver un nouveau phénomène à l'intersection entre les deux: les structures localisées excitables. D'une part nous avons étudié les propriétés des structures localisées qui se forment dans un laser à solitons. Celui-ci est constitué par deux laser à semiconducteur à cavité verticale (VCSEL) mutuellement couplées dans une configuration de laser avec absorbant saturable (LSA). Nous observons l'émissions aléatoire et localisée d'impulsions que nous affirmons être la première évidence expérimentale de structures localisées excitables. D'autre part nous avons démontré le comportement excitable d'un laser avec signal injecté par la possibilité de contrôler les impulsions excitable grâce à une perturbation externe appropriée. Nous avons également réalisé des simulations numériques qui montrent l'existence des structures localisées excitables dans un modèle de VCSEL avec absorbant saturable.Excitability and localized structures are universal phenomena, observed in various systems. Both possess interesting properties for potential applications, especially in optics. Excitability is the intrinsic property of the neuron defining its response to an external stimulus: for a sub-threshold stimulus the neuron stays quiescent; for a super-threshold stimulus, it emits a well-calibrated pulse independent on the strength of the stimulus. Localized structures in optics are bright intensity peaks coexisting with a homogeneous low intensity background. They appear in the transverse section of spatially-extended laser resonators. We study the occurrence of these nonlinear phenomena in semiconductor microcavities since the applications in all-optical processing of information are promising. Moreover we investigate the possibility of a novel kind of localized structure which stands at the intersection of these two phenomena: the excitable localized structures. On the one hand we study the properties of localized structures arising from a cavity soliton laser composed of two mutually coupled broad-area VCSELs in a LSA (Laser with Saturable Absorber) configuration . We report on the observation of a random and localized emission of pulses which we claim to be the first experimental evidence of noise-triggered excitable localized structures whose excitability is induced by inhomogeneities and drift. On the other hand we demonstrate the excitability in an optically injected laser by showing the control of excitable pulses by means of an external perturbation. We also perform numerical simulations which reveal the existence of excitable localized structures in a model of broad area VCSEL with saturable absorber

Excitabilité et structures localisées laser dans les microcavités à semi-conducteur

Excitability and localized structures are universal phenomena, observed in various systems. Both possess interesting properties for potential applications, especially in optics. Excitability is the intrinsic property of the neuron defining its response to an external stimulus: for a sub-threshold stimulus the neuron stays quiescent; for a super-threshold stimulus, it emits a well-calibrated pulse independent on the strength of the stimulus. Localized structures in optics are bright intensity peaks coexisting with a homogeneous low intensity background. They appear in the transverse section of spatially-extended laser resonators. We study the occurrence of these nonlinear phenomena in semiconductor microcavities since the applications in all-optical processing of information are promising. Moreover we investigate the possibility of a novel kind of localized structure which stands at the intersection of these two phenomena: the excitable localized structures. On the one hand we study the properties of localized structures arising from a cavity soliton laser composed of two mutually coupled broad-area VCSELs in a LSA (Laser with Saturable Absorber) configuration . We report on the observation of a random and localized emission of pulses which we claim to be the first experimental evidence of noise-triggered excitable localized structures whose excitability is induced by inhomogeneities and drift. On the other hand we demonstrate the excitability in an optically injected laser by showing the control of excitable pulses by means of an external perturbation. We also perform numerical simulations which reveal the existence of excitable localized structures in a model of broad area VCSEL with saturable absorber.Excitabilité et structures localisées sont des phénomènes universels qui ont été observés dans une grande variété de systèmes. Chacun des deux phénomènes a des propriétés intéressante pour des applications potentielles, surtout dans l'optique. L'excitabilité est la propriété intrinsèque du neurone, elle décrit sa réponse à une stimulation: pour des stimulations en-dessous d'un certain seuil, le neurone reste dans son état de repos mais quand la stimulation dépasse ce seuil, il émet une impulsion dont la taille ne dépend pas de la force de la stimulation. Les structures localisées dans les systèmes optiques sont des pics de surintensité qui coexistent avec un fond homogène sur la section transversale spatialement étendue d'une cavité laser. Dans cette thèse nous avons étudié l'apparition de ces deux phénomènes non-linéaires dans des microcavités à semi-conducteur, pour lesquelles les applications dans le traitement tout-optique de l'information sont prometteuse. En outre, nous avons étudié la possibilité de trouver un nouveau phénomène à l'intersection entre les deux: les structures localisées excitables. D'une part nous avons étudié les propriétés des structures localisées qui se forment dans un laser à solitons. Celui-ci est constitué par deux laser à semiconducteur à cavité verticale (VCSEL) mutuellement couplées dans une configuration de laser avec absorbant saturable (LSA). Nous observons l'émissions aléatoire et localisée d'impulsions que nous affirmons être la première évidence expérimentale de structures localisées excitables. D'autre part nous avons démontré le comportement excitable d'un laser avec signal injecté par la possibilité de contrôler les impulsions excitable grâce à une perturbation externe appropriée. Nous avons également réalisé des simulations numériques qui montrent l'existence des structures localisées excitables dans un modèle de VCSEL avec absorbant saturable

Mitigation of Parametric Instability

International audienceA key action for enhancing the sensitivity of gravitational wave (GW) detectors based on laser interferometry is to increase the laser power. However, in such a high-power regime, a nonlinear optomechanical phenomenon called parametric instability (PI) leads to the amplification of the mirrors vibrational modes preventing the detector functioning. Thus this phenomenon limits the detectors maximum power and so its performances. Our group has started an experimental research program aiming at realizing a exible and active mitigation system, based on the radiation pressure applied by an auxiliary laser. A summary on the PI mitigation techniques will be presented, we will explain the working principle of the system that we are implementing and report about the first experimental results

High speed, high power 2D beam steering for mitigation of optomechanical parametric instability in gravitational wave detectors

In this paper we propose a novel strategy to control optomechanical parametric instability (PI) in gravitational wave (GW) detectors, based on radiation pressure. The fast deflection of a high power beam is the key element of our approach. We built a 2D deflection system based on a pair of acousto-optic modulators (AOMs) that combines high rapidity and large scan range. As fast frequency switching configurable AOM driver we used an Universal Software Radio Peripheral (USRP) combined with a high performance personal computer (PC). In this way we demonstrate a 2D beam steering system with flat efficiency over the whole scan range and with a transition time of 50 ns between two arbitrary consecutive deflection positions for a beam power of 3.6 W

Mutual coherence of laser solitons in coupled semiconductor resonators

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Higher-order Hermite-Gauss modes for gravitational waves detection

International audienceAs part of the research on thermal noise reduction in gravitational-wave detectors, we experimentally demonstrate the conversion of a fundamental TEM00 laser mode at 1064 nm to higher-order Hermite-Gaussian modes (HG) of arbitrary order via a commercially available liquid crystal spatial light modulator. We particularly studied the HG5,5/HG10,10/HG15,15 modes. A two-mirror plano-spherical cavity filters the higher-order modes spatially. We analyze the cleaned modes via a three-mirror diagnosis cavity and measure a mode purity of 96/93/78% and a conversion efficiency of 6.6%/3.7%/1.7%, respectively. A full set of simulations and mathematical proofs are also presented which shows that (i) Hermite-Gauss modes resonate in a two-mirror cavity provided mirrors are properly angled with respect to the impinging mode, and (ii) Hermite-Gauss modes resonate in triangular cavities. Hence, higher-order Hermite-Gauss modes are compatible with ground-based gravitational-wave detectors’ architecture and can be employed for the mitigation of mirror thermal noise for the third generation Einstein Telescope or Cosmic Explorer