85 research outputs found
Dick effect in a pulsed atomic clock using Coherent Population Trapping
The Dick effect can be a limitation of the achievable frequency stability of
a passive atomic frequency standard when the ancillary frequency source is only
periodically sampled. Here we analyze the Dick effect for a pulsed vapor cell
clock using coherent population trapping (CPT). Due to its specific
interrogation process without atomic preparation nor detection outside of the
Ramsey pulses, it exhibits an original shape of the sensitivity function to
phase noise of the oscillator. Numerical calculations using a three-level atom
model are successfully compared with measurements; an approximate formula of
the sensitivity function is given as an easy-to-use tool. A comparison of our
CPT clock sensitivity to phase noise with a clock of the same duty cycle using
a two-level system reveals a higher sensitivity in the CPT case. The influence
of a free-evolution time variation and of a detection duration lengthening on
this sensitivity is studied. Finally this study permitted to choose an adapted
quartz oscillator and allowed an improvement of the clock fractional frequency
stability at the level of 3.2x10-13 at 1
Tunable high-purity microwave signal generation from a dual-frequency VECSEL at 852 nm (orale)
International audienceWe demonstrate the dual-frequency emission of a diode-pumped vertical external-cavity semiconductor laser operating at 852 nm, dedicated to the coherent population trapping of cesium atoms for compact atomic frequency references. It is based on a single laser cavity sustaining the oscillation of two adjacent, cross-polarized, modes. The output power reaches 10 mW on each frequency. The frequency difference and the absolute laser frequencies are simultaneously precisely tuned and stabilized on external references, resulting in the generation of a high-purity optically-carried microwave signal. The laser design has focused on stability and compactness
Emission bifréquence d'un laser à semiconducteur en cavité externe à 852 nm pour les horloges atomiques a césium (orale)
National audienceNous décrivons l'émission simultanée en phase, sur deux fréquences optiques polarisées perpendiculairement, d'un laser à semiconducteur en cavité externe pompé optiquement. L'émission est accordable autour de la raie D2 du césium à 852,14 nm avec une puissance optique d'environ 13 mW sur chaque polarisation. La différence de fréquence est ajustée grùce à un modulateur électro-optique autour de 9,2 GHz. Nous évaluons la source réalisée en vue de son application au piégeage cohérent de population d'atomes de césium dans une horloge atomique
Evaluation of the noise properties of a dual-frequency VECSEL for compact Cs atomic clocks (Poster)
International audienceWe evaluate a dual-frequency and dual-polarization optically-pumped semiconductor laser emitting at 852 nm as a new laser source for compact atomic clocks based on the coherent population trapping (CPT) technique. The frequency difference between the laser modes is tunable to 9.2 GHz corresponding to the ground state hyperfine-split of Cs. Impact of the laser noise has been investigated. Laser relative intensity noise is limited by the pump-RIN transfer to a level of-110 dB/Hz. Laser frequency noise shows excess mechanical and technical noise resulting in a laser linewidth of 1 MHz at 1 s in lock operation. The noise performance and spectral properties of the laser are already adequate to realize CPT experiments and should result in Allan standard-deviation of the clock below 1 Ă 10-12 at 1 second
Two-cross-polarized-frequency VECSEL at 852nm for CPT-based Cs clocks (poster)
International audienceWe demonstrate a tunable high-purity microwave signal generation from a cross- polarized dual-frequency diode-pumped vertical external-cavity semiconductor laser operating at 852 nm for the coherent population trapping of cesium atoms in compact atomic frequency references
Low-noise dual-frequency laser for compact Cs atomic clocks
International audienceWe report the dual-frequency and dual-polarization emission of an optically-pumped vertical external-cavity semiconductor laser (OP-VECSEL). Our laser source provides a high-purity optically-carried RF signal tunable in the GHz range, and is specifically designed for the coherent population trapping (CPT) of Cs atoms in compact atomic clocks. The laser spectrum is stabilized onto a Cs atomic transition at 852.1 nm, and the frequency difference is locked to a local oscillator at 9.2 GHz. Special attention has been paid to the evaluation of the frequency, intensity and phase noise properties. A maximum phase noise of - 90 dBrad2/Hz has been measured. Finally, we estimate the contribution of the laser noise on the short-term frequency stability of a CPT atomic clock, and predict that a value below 3 Ă 10-13 over one second is a realistic target
Generation of high purity microwave signal from a dual-frequency OP-VECSEL (orale)
International audienceCoherent population trapping (CPT) is an interesting technique for the development of compact atomic frequency references. We describe an innovating laser source for the production of the two cross-polarized coherent laser fields which are necessary in CPT-based atomic clocks. It relies on the dual-frequency and dual-polarization operation of an optically-pumped vertical external-cavity semiconductor laser. This particular laser emission is induced by intracavity birefringent components which produce a controllable phase anisotropy within the laser cavity and force emission on two cross-polarized longitudinal modes. The laser emission is tuned at the Cs D2 line (λ = 852.14 nm), and the frequency difference âÎœ between the two laser modes is tunable in the microwave range. The laser line wavelength is stabilized onto an atomic hyperfine transition, and concurrently the frequency difference is locked to an ultra-low noise RF oscillator at 9.2 GHz. The high spectral purity of the optically-carried microwave signal resulting from the beatnote of the two cross-polarized laser lines is assessed through its narrow spectral linewidth (<30 Hz) as well as its low phase noise (†-100 dBrad2/Hz). The performance of this laser source is already adequate for the interrogation of atoms in a CPT atomic clock, and should result in an estimated relative stability of 3.10-13Ï-1/2 - one order of magnitude better than commercial atomic clocks
High-purity microwave signal from a dual-frequency semiconductor laser for CPT atomic clocks (poster)
Coherent population trapping (CPT) of metal-alkali atoms is an interesting technique for the development of compact atomic frequency references; it relies on the excitation of the atoms by two phase-coherent laser fields. We describe the design and operation of an innovating dual-frequency laser source dedicated to Cs CPT atomic clocks, based on the direct dual-frequency and dual-polarization operation of an optically-pumped semiconductor laser at 852 nm. The phase noise of beatnote generated by the laser source is at maximum of -90 dBradÂČ/Hz with active stabilization, and the relative intensity noise (RIN) has been measured at -115 dB/Hz. It would potentially results in a clock frequency stability of 1.6 .10^-12 at 1 second, limited by the laser RIN. With proper adjustments in the laser and clock set-up, we target a stability of 3.10^-13 at 1 second
Horloge atomique à piégeage cohérent de population du césium en cellule : limitations à la stabilité de fréquence
This report refers to the frequency stability study of a compact clock using coherent population trapping. The frame of such a study is firstly to deal in depth with the understanding of the systematic effects affecting the frequency of a coherent population trapping resonance. A second goal is to build a state-of-the-art compact atomic clock. Because of a pulsed interrogation and laser beams linearly and orthogonally polarized, our prototype would present a fractional frequency stability distinctly below 10^-13 at 1 s integration if it was shot-noise limited. Further to a setup description, the first part of this report is devoted to study the noise sources which limit the short-term stability of the clock. A special attention has been paid to model, experiment and reduce the transfer of local oscillator frequency noise and of laser intensity noise to microwave frequency noise. It led to measure an interesting stability measurement at the level of 3.2x10^-13 at 1 s. An experimental and theoretical study of the frequency shift due to laser intensity fluctuation is then presented. Beyond the influence on this shift of dark resonance overlapping that has been enlighted, this study gives the basics to understand the insensibilization method of the frequency to power fluctuations presented in the last chapter.Ce mĂ©moire porte sur lâĂ©tude de la stabilitĂ© de frĂ©quence dâune horloge atomique Ă piĂ©geage cohĂ©rent de population. Le cadre de cette Ă©tude est dâune part dâapprofondir la connaissance du piĂ©geage cohĂ©rent de population en cellule de vapeur et dâautre part de construire un prototype dâhorloge dĂ©montrant une stabilitĂ© de frĂ©quence Ă lâĂ©tat de lâart des meilleures horloges compactes de laboratoire. GrĂące Ă une interrogation impulsionnelle et un schĂ©ma dâexcitation en polarisations linĂ©aires et orthogonales, cette horloge prĂ©senterait une stabilitĂ© de frĂ©quence relative nettement infĂ©rieure Ă 10^-13 Ă 1 s si elle Ă©tait limitĂ©e par un bruit fondamental tel que le bruit de photon. AprĂšs une prĂ©sentation du montage expĂ©rimental, la premiĂšre partie de ce mĂ©moire est consacrĂ©e Ă lâĂ©tude des diffĂ©rentes sources de bruit limitant la stabilitĂ© de frĂ©quence court-terme. Le soin particulier donnĂ© Ă la modĂ©lisation, Ă la caractĂ©risation expĂ©rimentale et Ă la rĂ©duction des transferts de bruit de frĂ©quence de lâoscillateur local (effet Dick) et du bruit dâintensitĂ© du laser en bruit de frĂ©quence de lâhorloge, a permis de mesurer une stabilitĂ© de frĂ©quence au niveau de 3.2x10^-13 Ă 1 s. Dans un deuxiĂšme temps une Ă©tude thĂ©orique et expĂ©rimentale du dĂ©placement de frĂ©quence micro-onde en fonction de la puissance laser est prĂ©sentĂ©e. Au-delĂ de la mise en Ă©vidence du caractĂšre clĂ© de la dĂ©formation de la raie dans lâexplication de ce dĂ©placement, elle a posĂ© les bases de la derniĂšre partie de ce mĂ©moire qui propose une mĂ©thode dâinsensibilisation du dĂ©placement de frĂ©quence aux fluctuations de puissance
Atomic clock using coherent population trapping in a cesium cell : limitations to the frequency stability
Ce mĂ©moire porte sur lâĂ©tude de la stabilitĂ© de frĂ©quence dâune horloge atomique Ă piĂ©geage cohĂ©rent de population. Le cadre de cette Ă©tude est dâune part dâapprofondir la connaissance du piĂ©geage cohĂ©rent de population en cellule de vapeur et dâautre part de construire un prototype dâhorloge dĂ©montrant une stabilitĂ© de frĂ©quence Ă lâĂ©tat de lâart des meilleures horloges compactes de laboratoire. GrĂące Ă une interrogation impulsionnelle et un schĂ©ma dâexcitation en polarisations linĂ©aires et orthogonales, cette horloge prĂ©senterait une stabilitĂ© de frĂ©quence relative nettement infĂ©rieure Ă 10^-13 Ă 1 s si elle Ă©tait limitĂ©e par un bruit fondamental tel que le bruit de photon. AprĂšs une prĂ©sentation du montage expĂ©rimental, la premiĂšre partie de ce mĂ©moire est consacrĂ©e Ă lâĂ©tude des diffĂ©rentes sources de bruit limitant la stabilitĂ© de frĂ©quence court-terme. Le soin particulier donnĂ© Ă la modĂ©lisation, Ă la caractĂ©risation expĂ©rimentale et Ă la rĂ©duction des transferts de bruit de frĂ©quence de lâoscillateur local (effet Dick) et du bruit dâintensitĂ© du laser en bruit de frĂ©quence de lâhorloge, a permis de mesurer une stabilitĂ© de frĂ©quence au niveau de 3.2x10^-13 Ă 1 s. Dans un deuxiĂšme temps une Ă©tude thĂ©orique et expĂ©rimentale du dĂ©placement de frĂ©quence micro-onde en fonction de la puissance laser est prĂ©sentĂ©e. Au-delĂ de la mise en Ă©vidence du caractĂšre clĂ© de la dĂ©formation de la raie dans lâexplication de ce dĂ©placement, elle a posĂ© les bases de la derniĂšre partie de ce mĂ©moire qui propose une mĂ©thode dâinsensibilisation du dĂ©placement de frĂ©quence aux fluctuations de puissance.This report refers to the frequency stability study of a compact clock using coherent population trapping. The frame of such a study is firstly to deal in depth with the understanding of the systematic effects affecting the frequency of a coherent population trapping resonance. A second goal is to build a state-of-the-art compact atomic clock. Because of a pulsed interrogation and laser beams linearly and orthogonally polarized, our prototype would present a fractional frequency stability distinctly below 10^-13 at 1 s integration if it was shot-noise limited. Further to a setup description, the first part of this report is devoted to study the noise sources which limit the short-term stability of the clock. A special attention has been paid to model, experiment and reduce the transfer of local oscillator frequency noise and of laser intensity noise to microwave frequency noise. It led to measure an interesting stability measurement at the level of 3.2x10^-13 at 1 s. An experimental and theoretical study of the frequency shift due to laser intensity fluctuation is then presented. Beyond the influence on this shift of dark resonance overlapping that has been enlighted, this study gives the basics to understand the insensibilization method of the frequency to power fluctuations presented in the last chapter
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