Ramsey-coherent population trapping Cs atomic clock based on lin‖lin optical pumping with dispersion detection

A Cs vapor cell-based atomic clock that uses a lin‖lin pumping scheme with dispersion detection is reported. This atomic clock shows potential for high performance because of its high contrast pumping scheme, and for miniaturization because of its simple architecture. The experimental setup and optimal operating parameters for the clock are introduced.The current fractional frequency stability is measured to be 1.3 × 10~(-12)/■ up to 20s and reaches 3.1 × 10~(-13) at 200 s. We have thoroughly investigated the related noise sources that affect clock frequency stability at the 1s and 100s levels. The investigation shows that the laser frequency noise limits the clock frequency stability significantly. The clock performance can be further improved by technically upgrading the laser frequency stabilization setup.     

Fluctuations de temperature et flux de chaleur en aval d'une source linéaire placée dans une couche limite turbulente

The purpose of the present communication is to present and discuss some recent experimental results concerning the dispersion downstream of a heated line source located, in a turbulent boundary layer, successively at two distances from an adiabatic wall. Information on the mean and fluctuating temperature fields and associated heat fluxes are presented and analysed by testing closure assumptions for model dispersion at first and second orders. This model, which only requires the use of temporal velocity scales of the flow, leads to a rather good agreement with measurements.     

Réalisabilité d'un schéma non linéaire de retour à l'isotropie de la corrélation pression-gradient d'un scalaire

The study of the equilibrium states of a homogeneous turbulence, in the absence of mean gradients, leads to an equilibrium solution with zero values for the turbulent scalar flows. Stability of this equilibrium solution is achieved by a simple condition on one of the coefficients of the model. A realisibility study of the turbulent scalar flow has been carried out an has led to a general realisibility condition imposed on the model coefficients. Moreover, it has been established that, if the return to isotropy is compatible with two supplementary constraints on the model coefficients, it is possible to substitute a sufficient yet much simpler condition for the general realisability condition. Finally, a numerical optimization on the basis of the experimental results and the direct simulation results, has proven that the proposed model ensures a better prediction of the scalar turbulence with respect to Rotta's model.