The Ramsey method has been applied by means of optical coherent population trapping (CPT) pulses through a cesium vapor cell with N/sub 2/ buffer gas at room temperature, using two phase-locked ...lasers. With this method, CPT resonance spectral widths are no longer limited by optical saturation and collision effects, but only depend on free evolution time between the two pulses. A fringe width below 100 Hz is reported. Experimental Raman-Ramsey fringes are analyzed using the classical wavefunction formalism.
Two projects of compact cold atom clocks are currently developed: a clock with atoms directly cooled in the microwave cavity and a clock based on coherent population trapping. For each device, ...different interrogation and detection schemes are evaluated and reported
3D speckle cooling in a microwave clock Pottie, P.-E.; Tremine, S.; Guerandel, S. ...
IEEE International Frequency Control Symposium and PDA Exhibition Jointly with the 17th European Frequency and Time Forum, 2003. Proceedings of the 2003,
2003
Conference Proceeding
Sub-Doppler laser cooling is studied in an optically polished microwave cavity used as a reflecting cell. Light potential wells due to the speckle field in the cell make Sisyphus cooling mechanisms ...possible. For a 1 s capture time, about 10/sup 8/ cesium atoms are cooled at temperatures in the microkelvin range from thermal vapor. These results are discussed and compared with the basic theoretical model involving two laser beams lin /spl perp/ lin polarized. For a microwave clock using such cold atoms, the pulsed operation is precised and the main frequency shifts are evaluated. The short term relative frequency stability is expected to be lower than 10/sup -12//spl tau//sup - 1/2 /.
HORACE is a compact cold Cs atom clock where laser cooling, microwave interrogation and clock signal detection are all performed inside a spherical microwave cavity. We present the signals observed ...on the new clock prototype. The frequency stability is estimated from clock signal measurements.
In the compact cold atoms clock HORACE caesium atoms are successively laser cooled, submitted to a Ramsey microwave interrogation scheme and then detected by linear absorption directly inside the ...microwave cavity. The whole physics package and optical bench have been entirely redesigned to optimize such an in-situ detection and to perform a normalization scheme. Main efforts have been concentrated on technical issues such as magnetic shielding, microwave cavity polishing and tuning, use of fast mechanical switches to realize the optical sequence.
The effects of cycloheximide (0.1-200 mg per litre) on the microbial community from the sediment-water interface of a lake were studied. Field grazing experiments were carried out to compare ...inhibition, dilution and filtration methods of determining grazing rates. Cycloheximide inhibited neither the autotrophs nor the mixed community of aerobic heterotrophs at any test concentration. The mixed culture of anaerobic heterotrophs was inhibited at 50 mg per litre and the mixed protozoan culture was inhibited at all test concentrations (25-200 mg per litre). The grazing experiment showed that bacterial growth rates determined using cycloheximide were different from those obtained by dilution and filtration treatments. Cycloheximide did not inhibit target micro-organisms but inhibited nontarget, anaerobic bacteria thus limiting its usefulness as a selective eukaryote inhibitor for grazing experiments.
Recent results on a pulsed CPT clock Zanon, T.; Tremine, S.; Guerandel, S. ...
Proceedings of the 2005 IEEE International Frequency Control Symposium and Exposition, 2005,
2005
Conference Proceeding
CPT clocks are very attractive for their miniaturization potentiality. Nevertheless, two main effects limit today their performance: the optical pumping associated with circularly polarized lasers ...and the line broadening due to saturation effects. We propose to overcome these limitations by the use of orthogonal linear laser polarizations and a pulsed interrogation sequence. The optimization of the time sequence leading to the best characteristics (contrast, linewidth) of the dark resonance is discussed. Very preliminary measurements of the frequency stability demonstrate an interesting performance of 3.5 10 -12 tau -frac12
HORACE is a compact cold atom clock where the atoms are cooled inside the microwave interrogation cavity. About 108 atoms can be cooled at kinetic temperatures as low as 2.5 μK. We report for the ...first time Ramsey pattern observed with a 14 Hz linewidth and fringe contrast better than 80%. Since this clock is designed for Space applications, some properties are extrapolated to micro-gravity operation.
The HORACE device is a compact cold atom clock where about 10/sup 8/ cesium atoms are laser cooled at a few /spl mu/K, then interrogated and detected directly in a 20 cm/sup 3/ spherical microwave ...cavity. The optimization of the short term stability with the cooling and interrogation durations is presented, leading to an estimation of the Allan deviation of /spl sigma//sub y/(/spl tau/) -1 10/sup -13/ /spl tau/ /sup - 1/2 /on earth and /spl sigma//sub y/(/spl tau/) = 7 10/sup -14/ /spl tau//sup -frac12;/ in space. The quantum projection noise, the Dick effect and the detection laser noises are taken into account. The calculations are based on a preliminary model for the recapture of cold atoms, in reasonable agreement with measurements.
Stability of the compact cold atom clock HORACE Esnault, F.X.; Perrin, S.; Tremine, S. ...
2007 IEEE International Frequency Control Symposium Joint with the 21st European Frequency and Time Forum
Conference Proceeding
HORACE is a compact cold cesium atom clock which is being developed in LNE-SYRTE for space applications and onboard systems. The operation of this clock is different from fountains since the laser ...cooling, the microwave interrogation and the detection are sequentially performed inside the spherical microwave cavity. We recently achieved short term stability of 5.5 10 -13 tau -0.5 reaching the 10 -14 level at 3000 sec. We report in this paper recent developments and improvements, particularly on the cooling sequence. We also study the main limitations.
