- Thomann, Pierre

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# Thomann, Pierre

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Thomann, Pierre

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pierre.thomann@unine.ch

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- PublicationMétadonnées seulementPump-probe spectroscopy and velocimetry of cold atoms in a slow beam(2001)
; ; Montrer plus In this paper we report on the first purely "pump-probe" nonlinear laser spectroscopy results in a slow atomic beam. We have observed Raman, Rayleigh, and recoil-induced resonances (RIR) in a continuous beam of slow and cold cesium atoms extracted from a two-dimensional (2D) magneto-optical-trap (MOT) with the moving molasses technique. The RIR enabled us to measure the velocity distribution. therefore the average speed (0.6-4 m/s) and temperature (50-500 muK) of the atomic beam. Compared to time of flight, this technique has the advantage of being local, more sensitive in the low-velocity regime (vMontrer plus - PublicationAccès libreExperimental Validation of a Simple Approximation to Determine the Linewidth of a Laser from its Frequency Noise Spectrum(2012-7-2)
; ; ; ; ; Montrer plus 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.Montrer plus - PublicationAccès libreOn the Stability of Optical Lattices(2005)
; ;Castagna, N. ;Plimmer, M. D.; ;Taichenachev, A.V.Yudin, V.I.Montrer plus In this article, we present an analysis of the stability of optical lattices. Starting with the study of an unstable optical lattice, we establish a necessary and sufficient condition for intrinsic phase stability and discuss two practical solutions to fulfill this condition, namely, minimal and folded optical lattices. We then present a particular example of a two-dimensional folded optical lattice, which has the advantages of being symmetric, possessing power recycling, and having a convenient geometry. We have used this lattice for laser collimation of a continuous cesium beam in a fountain geometry.Montrer plus - PublicationAccès libreLinewidth of a quantum cascade laser assessed from its frequency noise spectrum and impact of the current driver(2012-4-21)
; ; ; ; ; Montrer plus 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.Montrer plus - PublicationMétadonnées seulementTheoretical study of the Dick effect in a continuously operated Ramsey resonator(2001)
; ; ;Dudle, GregorMontrer plus It is well established that passive frequency standards operated in pulsed mode may suffer a degradation of their frequency stability due to the frequency (FM) noise of the Local Oscillator CLO). In continuously operated frequency standards, it has been shown that a similar degradation of the frequency stability may arise, depending on the used modulation-demodulation scheme. In this paper, we report a theoretical analysis on the possible degradations of the frequency stability of a continuous fountain due to the LO FM noise, A simple model is developed to evaluate whether or not aliasing persists. This model is based on a continuous frequency control loop of a frequency standard using a Ramsey resonator. From this model, we derive a general formula, valid for all usual modulation-demodulation schemes, for the LO frequency fluctuations due to aliasing in closed loop operation. We demonstrate that in an ideal situation and for all usual modulation waveforms, no aliasing occurs if the half-period of modulation equals the transit time of atoms in the Ramsey resonator. The also deduce that in the same conditions,- square-wave phase modulation provides the strongest cancellation of the LO instabilities in closed loop operation. Finally, we show that the "Dick formula" for the specific case of the pulsed fountain can be recovered from the model by a sampling operation.Montrer plus - PublicationAccès libreCombined quantum state preparation and laser cooling of a continuous beam of cold atoms(2010)
; ; ;Dumas, ClaireMontrer plus We use two-laser optical pumping on a continuous atomic fountain in order to prepare cold cesium atoms in the same quantum ground state. A first laser excites the F=4 ground state to pump the atoms toward F=3 while a second π -polarized laser excites the F=3 -> F'=3 transition of the D2 line to produce Zeeman pumping toward m=0. To avoid trap states, we implement the first laser in a 2D optical lattice geometry, thereby creating polarization gradients. This configuration has the advantage of simultaneously producing Sisyphus cooling when the optical lattice laser is tuned between the F=4 -> F'=4 and F=4 -> F'=5 transitions of the D2 line, which is important to remove the heat produced by optical pumping. Detuning the frequency of the second π-polarized laser reveals the action of a new mechanism improving both laser cooling and state preparation efficiency. A physical interpretation of this mechanism is discussed.Montrer plus - PublicationMétadonnées seulementSelf-aligned extended-cavity diode laser stabilized by the Zeeman effect on the cesium D-2 line(2000)
;Lecomte, Steve ;Fretel, Emmanuel; Montrer plus An extended-cavity diode laser at 852 nm has been built especially for the purpose of cooling and probing cesium atoms. It is a compact, self-aligned, and continuously tunable laser source having a 100-kHz linewidth and 60-mW output power. The electronic control of the laser frequency by the piezodriven external reflector covers a 4.5-kHz bandwidth, allowing full compensation of acoustic frequency noise without any adverse effect on the laser intensity noise. We locked this laser to Doppler-free resonances on the cesium D-2 line by using the Zeeman modulation technique, resulting in the frequency and the intensity of the laser beam being unmodulated. We also tuned the locked laser frequency over a span of 120 MHz by using the de Zeeman effect to shift the F = 4-F' = 5 reference transition. (C) 2000 Optical Society of America. OCIS codes: 140.2020, 140.3570, 140.3600, 260.7490, 300.6460.Montrer plus - PublicationAccès libreSimple approach to the relation between laser frequency noise and laser line shape(2010-8-30)
; ; Montrer plus Frequency fluctuations of lasers cause a broadening of their line shapes. Although the relation between the frequency noise spectrum and the laser line shape has been studied extensively, no simple expression exists to evaluate the laser linewidth for frequency noise spectra that does not follow a power law. We present a simple approach to this relation with an approximate formula for evaluation of the laser linewidth that can be applied to arbitrary noise spectral densities.Montrer plus - PublicationMétadonnées seulementRecherches sur les horloges atomiques miniatures et optiques(2007)
; ; ;Breschi, Evelina; ; Montrer plus - PublicationAccès libreFrequency noise of free-running 4.6 um distributed feedback quantum cascade lasers near room temperature(2011-8-10)
; ; ; ; ;Faist, J.; Montrer plus The frequency noise properties of commercial distributed feedback quantum cascade lasers emitting in the 4.6 um range and operated in cw mode near room temperature (277K) are presented. The measured frequency noise power spectral density reveals a flicker noise dropping down to the very low level of <100 Hz2/Hz at 10 MHz Fourier frequency and is globally a factor of 100 lower than data recently reported for a similar laser operated at cryogenic temperature. This makes our laser a good candidate for the realization of a mid-IR ultranarrow linewidth reference.Montrer plus