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Thomann, Pierre
Nom
Thomann, Pierre
Affiliation principale
Fonction
Professeur honoraire
Email
pierre.thomann@unine.ch
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Voici les éléments 1 - 10 sur 50
- PublicationAccès libreExperimental techniques for optical frequency metrology(2014)
- PublicationAccès libreCross-influence between the two servo-loops of a fully-stabilized Er:fiber optical frequency comb(2012-9-28)
; ; ; ; ; We present a study of the impact of the cross-coupling between the two servo loops used to stabilize the repetition rate frep and the carrier-envelope offset (CEO) frequency fCEO in a commercial Er:fiber frequency comb, based on the combination of experimental measurements and a model of the coupled loops. The developed theoretical model enables us to quantify the influence of the servo-loop coupling on an optical comb line, by simulating the hypothetic case where no coupling would be present. Numerical values for the model were obtained from an extensive characterization of the comb, in terms of frequency noise and dynamic response to a modulation applied to each actuator, for both frep and fCEO. To validate the model, the frequency noise of an optical comb line at 1.56 μm was experimentally measured from the heterodyne beat between the comb and a cavity-stabilized ultranarrow-linewidth laser and showed good agreement with the calculated noise spectrum. The coupling between the two stabilization loops results in a more than 10-fold reduction of the comb mode frequency noise power spectral density in a wide Fourier frequency range. - PublicationAccès libreExperimental Validation of a Simple Approximation to Determine the Linewidth of a Laser from its Frequency Noise Spectrum(2012-7-2)
; ; ; ; ; Laser frequency fluctuations can be characterized either comprehensively by the frequency noise spectrum or in a simple but incomplete manner by the laser linewidth. A formal relation exists to calculate the linewidth from the frequency noise spectrum, but it is laborious to apply in practice. We recently proposed a much simpler geometrical approximation applicable to any arbitrary frequency noise spectrum. Here we present an experimental validation of this approximation using laser sources of different spectral characteristics. For each of them, we measured both the frequency noise spectrum to calculate the approximate linewidth and the actual linewidth directly. We observe a very good agreement between the approximate and directly measured linewidths over a broad range of values (from kilohertz to megahertz) and for significantly different laser line shapes. - PublicationAccès libreNoise properties of an optical frequency comb from a SESAM-modelocked 1.5 µm solid-state laser stabilized to the 10E-13 level(2012-5-26)
; ; ; ; ; ; - PublicationAccès libreLinewidth of a quantum cascade laser assessed from its frequency noise spectrum and impact of the current driver(2012-4-21)
; ; ; ; ; We report on the measurement of the frequency noise properties of a 4.6-μm distributed-feedback quantum-cascade laser (QCL) operating in continuous wave near room temperature using a spectroscopic set-up. The flank of the R(14) ro-vibrational absorption line of carbon monoxide at 2196.6 cm^−1 is used to convert the frequency fluctuations of the laser into intensity fluctuations that are spectrally analyzed. We evaluate the influence of the laser driver on the observed QCL frequency noise and show how only a low-noise driver with a current noise density below ≈1 nA/√Hz allows observing the frequency noise of the laser itself, without any degradation induced by the current source. We also show how the laser FWHM linewidth, extracted from the frequency noise spectrum using a simple formula, can be drastically broadened at a rate of ≈1.6 MHz/(nA/√Hz) for higher current noise densities of the driver. The current noise of commercial QCL drivers can reach several nA/√Hz , leading to a broadening of the linewidth of our QCL of up to several megahertz. To remedy this limitation, we present a low-noise QCL driver with only 350 pA/√Hz current noise, which is suitable to observe the ≈550 kHz linewidth of our QCL. - PublicationAccès libreTemperature dependence of the frequency noise in a mid-IR DFB quantum cascade laser from cryogenic to room temperature(2012)
; ; ; We report on the measurement of the frequency noise power spectral density in a distributed feedback quantum cascade laser over a wide temperature range, from 128 K to 303 K. As a function of the device temperature, we show that the frequency noise behavior is characterized by two different regimes separated by a steep transition at ≈200 K. While the frequency noise is nearly unchanged ~200 K, it drastically increases at lower temperature with an exponential dependence. We also show that this increase is entirely induced by current noise intrinsic to the device. In contrast to earlier publications, a single laser is used here in a wide temperature range allowing the direct assessment of the temperature dependence of the frequency noise. - PublicationAccès libreExperimental validation of a simple approximation to determine the linewidth of a laser from its frequency noise spectrumLaser frequency fluctuations can be characterized either comprehensively by the frequency noise spectrum or in a simple but incomplete manner by the laser linewidth. A formal relation exists to calculate the linewidth from the frequency noise spectrum, but it is laborious to apply in practice. We recently proposed a much simpler geometrical approximation applicable to any arbitrary frequency noise spectrum. Here we present an experimental validation of this approximation using laser sources of different spectral characteristics. For each of them, we measured both the frequency noise spectrum to calculate the approximate linewidth and the actual linewidth directly. We observe a very good agreement between the approximate and directly measured linewidths over a broad range of values (from kilohertz to megahertz) and for significantly different laser line shapes.
- PublicationAccès libreÉvaluation métrologique de l'étalon primaire de fréquence à atomes froids de césium FOCS-2(2012)
; ; Ce travail de recherche s'inscrit dans la continuité des études, menées depuis 20 ans à l'Observatoire Cantonal de Neuchâtel, pour réaliser un étalon primaire de fréquence fonctionnant avec un jet continu d'atomes froids et lents. Ces développements théoriques et expérimentaux ont conduit à la construction de deux horloges à fontaine continue FOCS-1 et FOCS-2. Ce document expose les dernières améliorations et les premières mesures d'évaluation du second étalon primaire de fréquence effectuées ces trois dernières années au Laboratoire Temps-Fréquence de l'Université de Neuchâtel.
Dans la première partie, nous présentons le développement et l'implémentation d'une nouvelle méthode de préparation d'état utilisée pour améliorer la stabilité de fréquence à court terme de l'étalon. Nous avons montré qu'en utilisant un schéma de pompage optique à deux lasers, il est possible de combiner simultanément préparation d'état et refroidissement Sisyphe. Grâce à cette technique, nous avons réussi à préparer 60% des atomes dans le niveau - PublicationAccès libreTheoretical analysis of aliasing noises in cold atom Mach-Zehnder interferometers(2012)
; ; We present a theoretical analysis of aliasing noises that might appear in cold atom Mach-Zehnder interferometers used for the measurement of various physical quantities. We focus more specifically on single cold atom gyroscopes. To evaluate the level of aliasing noises, we have developed a model based on the power spectral densities of the different identified noise sources as input parameters and which makes use of a servo-loop to realize a precise measurement of the rotation rate. The model allows one to take into account different modes of operation, like a continuous as well as a pulsed or even a multi-ball operation. For monokinetic atoms, we show that the intermodulation noise can be completely filtered out with a continuous mode of operation and an optimum modulation scheme for any modulation frequency but also with a pulsed operation however only for specific launching frequencies. In the case of a real continuous atomic beam having a velocity distribution, it comes out that a high attenuation can be reached which indicates clearly the potential stability improvement that can be expected from a continuous operation. - PublicationAccès libreImprovement of the frequency stability below the dick limit with a continuous atomic fountain clock(2012)
; ; ; The frequency instability of a shot-noise limited atomic fountain clock is inversely proportional to its signal-to- noise ratio. Therefore, increasing the atomic flux is a direct way to improve the stability. Nevertheless, in pulsed operation, the local oscillator noise limits the performance via the Dick effect. We experimentally demonstrate here that a continuous atomic fountain allows one to overcome this limitation. In this work, we take advantage of two-laser optical pumping on a cold cesium beam to increase the useful fountain flux and, thus, to reduce the frequency instability below the Dick limit. A stabil- ity of 6 • 10-14 τ-1/2 has been measured with the continuous cesium fountain FOCS-2.