Search

Brownian motion in confinement and at interfaces is a canonical situation, encountered from fundamental biophysics to nanoscale engineering. Using the Lorenz-Mie framework, we optically record the thermally-induced tridimensional trajectories of individual microparticles, within water, and in the vicinity of a rigid wall. Based on this data, we implement a novel, robust and self-calibrated multifitting method, allowing for the thermal-noise-limited inference of spatially-resolved diffusion coefficients, equilibrium potentials, and forces -- at the femtoNewton resolution.

International audience

International audience; We report the observation of the very narrow 4d105s 2S1/2→4d95s2 2D5/2 transition in atomic silver. The frequencies of the hyperfine components in 107Ag and 109Ag have been measured using Doppler-free twophoton laser spectroscopy of a thermal beam and heterodyne calibration with respect to the a1 component of the 62P(4-5) line in molecular iodine near 661 nm. For the center of gravity of a mixture of natural abundance, we deduce the value 906 641 295.77(19) MHz. For the isotope shift, we obtain nu(109Ag)−nu(107Ag) =564.1537 MHz, from which we deduce the frequency and isotope shift of the 4d105s 2S1/2→4d106p 2P3/2 transition at 206 nm

International audience; We demonstrate an original solution to obtain a single-frequency ring laser coupled to an external passive nonresonant ring cavity, which plays the role of an optical diode. This system provides more output power than systems with an intracavity unidirectional device. To the best of our knowledge, this work marks the first demonstration of a unidirectional planar ring laser at 1.3 _m. Using 12 W at 797 nm to pump a Nd:YLF laser, combined with intracavity second-harmonic generation, we achieve yields of 440 mW at 661.3 nm and 340 mW at 656.0 nm

This work deals with thedevelopment of an clock based on a two-photon transition in Ag at661 nm, whose natural width is about 1 Hz. To take advantage ofthe quality factor of the resonance, it will be necessary to uselaser-cooled atoms, the required wavelength being 328 nm. Thisthesis describes the design and construction of solid-state lasersallowing one to simplify the present apparatus. Diode-pumpedNd:YLF crystals enable one to generate both 1322 and 1312 nm.The second harmonic of the former will provide 661 nm while twicefrequency doubling the later will yield 328 nm. We have developeda theoretical model including thermal effects and Augerrecombination in order to design several prototype configurations(linear, twisted mode and re-injected ring cavities). Using thelast of these, we have built single-mode c.w. lasers at both 1312and 1322 nm with outputs of up to 2 W. By intra-cavity frequencydoubling therewith, we have obtained 440 mW at 661 nm and 340 mWat 656 nm. In addition, we have evaluated transition probabilitesusing the Cowan codes, both to estimate two-photon excitationrates and calculate the lifetime of the metastable level, hitherto obtained by comparisonwith an analogous transition in Hg+.; Ce travail de thèse s'inscrit dansle cadre du développement d'une horloge optique basée sur unetransition à deux photons de 661 nm de l'Ag de largeur naturelle~1 Hz. Afin de profiter du facteur de qualité de larésonance, il faudra travailler sur un échantillon d'atomesrefroidis par laser, la longueur d'onde nécessaire étant de 328nm. Ce mémoire concerne plus précisément la mise au point desources lasers solides pour améliorer la fiabilité de l'expérienceactuelle. Le cristal laser de Nd:YLF, pompé par diode laser,permet d'accéder aux longueurs d'onde 1322 nm et 1312 nm. Ledoublage en fréquence de la première source fournira la radiationà 661 nm tandis que deux étapes de doublage permettront d'obtenir,à partir des photons à 1312 nm, une onde à 656 nm puisune onde à 328 nm. Nous avons développé un modèle théorique, tenantcompte des effets thermiques et notamment des processus derecombinaison Auger, afin de dimensionner différentesconfigurations laser à tester (cavité linéaire, à mode hélicoïdal,cavité en anneau réinjectée). Grâce à la dernière, nous avonsréalisé des sources continues, monomodes, d'environ 2 W, à 1322nm et à 1312 nm. Ces cavités se prêtant au doublage de fréquence,nous avons obtenu des puissances de 440 mW à 661 nm et 340 mW à656 nm. Par ailleurs, une étude théorique des probabilités detransition de l'atome d'argent à l'aide des codes de Cowan a étéentreprise, afin d'une part de chiffrer l'ordre de grandeur de lapuissance laser nécessaire et d'autre part, d'estimer la durée devie du niveau métastable, jusqu'alors obtenueuniquement par comparaisonavec une transition quadrupolaire de l'ion mercure.

This work deals with thedevelopment of an clock based on a two-photon transition in Ag at661 nm, whose natural width is about 1 Hz. To take advantage ofthe quality factor of the resonance, it will be necessary to uselaser-cooled atoms, the required wavelength being 328 nm. Thisthesis describes the design and construction of solid-state lasersallowing one to simplify the present apparatus. Diode-pumpedNd:YLF crystals enable one to generate both 1322 and 1312 nm.The second harmonic of the former will provide 661 nm while twicefrequency doubling the later will yield 328 nm. We have developeda theoretical model including thermal effects and Augerrecombination in order to design several prototype configurations(linear, twisted mode and re-injected ring cavities). Using thelast of these, we have built single-mode c.w. lasers at both 1312and 1322 nm with outputs of up to 2 W. By intra-cavity frequencydoubling therewith, we have obtained 440 mW at 661 nm and 340 mWat 656 nm. In addition, we have evaluated transition probabilitesusing the Cowan codes, both to estimate two-photon excitationrates and calculate the lifetime of the metastable level, hitherto obtained by comparisonwith an analogous transition in Hg+.; Ce travail de thèse s'inscrit dansle cadre du développement d'une horloge optique basée sur unetransition à deux photons de 661 nm de l'Ag de largeur naturelle~1 Hz. Afin de profiter du facteur de qualité de larésonance, il faudra travailler sur un échantillon d'atomesrefroidis par laser, la longueur d'onde nécessaire étant de 328nm. Ce mémoire concerne plus précisément la mise au point desources lasers solides pour améliorer la fiabilité de l'expérienceactuelle. Le cristal laser de Nd:YLF, pompé par diode laser,permet d'accéder aux longueurs d'onde 1322 nm et 1312 nm. Ledoublage en fréquence de la première source fournira la radiationà 661 nm tandis que deux étapes de doublage permettront d'obtenir,à partir des photons à 1312 nm, une onde à 656 nm puisune onde à 328 nm. Nous avons développé un modèle théorique, tenantcompte des effets thermiques et notamment des processus derecombinaison Auger, afin de dimensionner différentesconfigurations laser à tester (cavité linéaire, à mode hélicoïdal,cavité en anneau réinjectée). Grâce à la dernière, nous avonsréalisé des sources continues, monomodes, d'environ 2 W, à 1322nm et à 1312 nm. Ces cavités se prêtant au doublage de fréquence,nous avons obtenu des puissances de 440 mW à 661 nm et 340 mW à656 nm. Par ailleurs, une étude théorique des probabilités detransition de l'atome d'argent à l'aide des codes de Cowan a étéentreprise, afin d'une part de chiffrer l'ordre de grandeur de lapuissance laser nécessaire et d'autre part, d'estimer la durée devie du niveau métastable, jusqu'alors obtenueuniquement par comparaisonavec une transition quadrupolaire de l'ion mercure.

International audience; We describe single-frequency operation of a diode-pumped Nd:YLF laser in the range 1311.9-1317.2 nm. It can be used for the interrogation of the clock transition in calcium (1314.0 nm) or spectroscopy in hydrogen and metastable singly ionized helium (1312.6 nm). By using a twisted-mode cavity, we have obtained output powers of 830 and 970mWat 1312.6 and 1314.0 nm, respectively, in a single longitudinal mode

International audience

International audience; The optical resonance linewidth of a single quantum emitter provides a direct measurement of decoherence in the system, which is a quantity of interest to certain quantum technological applications and ultimately sets a fundamental limitation for these materials. However, accessing the homogeneous linewidth has proven problematic in semiconductor nanocrystals (NCs) due to the effect of spectral diffusion (SD), which is a random fluctuation of the transition energy. Instabilities in the spectral position are discouraging for potential applications in for example coherent control of quantum states and coupled systems, thus so far there have been few reports using NCs in such applications. At cryogenic temperatures high quality NCs exhibit slow relaxation between closely spaced band-edge states resulting in stable multiline spectra. Inter-state relaxation properties are explored using a near-resonant photoluminescence excitation of higher-lying states to selectively excite specific band-edge states, revealing significant population redistribution, indicative of slow relaxation between the band-edge states. This state-selective excitation reveals unexpected spin-dependent non-radiative relaxation channels that need to be taken into account in order to understand the final state populations. In colloidal NCs, thermal excitation of acoustic phonons can be inhibited at cryogenic temperatures, eliminating a major dephasing mechanism, therefore one might expect to observe lifetime limited transitions in high quality colloidal NCs. High-resolution excitation scans of individual spectral lines of apparently ultra-stable NCs, reveal spectral lines significantly broader than the lifetime limit. By performing a series of successive scans over the same spectral line, the underlying SD is revealed. This SD is notable in that it results in symmetric broadening of the excitation scan, indicating that the origin is not photo-induced. Thus a persistent contribution to SD is revealed. The magnitudes of the spectral shifts are consistent with environmental charge noise known to be associated with random polymer matrices and so most likely emanate from the disordered local environment of the NC, which may include the ligand shell. This persistent SD ultimately limits the linewidth of the band-edge states in colloidal NCs to the 1 GHz regime, approximately an order of magnitude greater than the lifetime limit.

National audience