O. Kozlova

Limitations of Long-Term Stability in a Coherent Population Trapping Cs Clock

Vapor cell atomic clocks exhibit reduced frequency stability for averaging time between about one hundred and a few thousand seconds. Here we report a study on the impact of the main parameters on the mid-to-long term instability of a buffer-gas vapor cell Cs clock, based on coherent population trapping (CPT). The CPT signal is observed on the Cs D1 line transmission, using a double Λ scheme and a Ramsey interrogation technique. The effects on the clock frequency of the magnetic field, the cell temperature, and the laser intensities are reported. We show in particular that the laser intensity shift is temperature dependent. Along with the laser intensity ratio and laser polarization properties, this is one of the most important parameters.

Measuring the Boltzmann constant by mid-infrared laser spectroscopy of ammonia

We report on our ongoing effort to measure the Boltzmann constant,

Temperature Dependence Cancellation of the Cs Clock Frequency in the Presence of Ne Buffer Gas

k_B,

Dissemination of thermodynamic temperature above the freezing point of silver

using the Doppler broadening technique on ammonia. This paper presents some of the improvements made to the mid-infrared spectrometer including the use of a phase-stabilized quantum cascade laser, a lineshape analysis based on a refined physical model and an improved fitting program 2 increasing the confidence in our estimates of the relevant molecular parameters, and a first evaluation of the saturation parameter and its impact on the measurement of k B. A summary of the systematic effects contributing to the measurement is given and the optimal experimental conditions for mitigating those effects in order to reach a competitive measurement of

Hyperfine coherence and population lifetime in Cs vapor cells

k_B

Recent progress on the pulsed CPT Cs clock at SYRTE

at a part per million accuracy level are outlined.

A Self-Validation Method for High-Temperature Thermocouples Under Oxidizing Atmospheres

The temperature dependence of the Cs clock transition frequency in a vapor cell filled with Ne buffer gas has been measured. The experimental setup is based on the coherent population trapping technique and a temporal Ramsey interrogation allowing a high resolution. A quadratic dependence of the frequency shift is shown. The temperature of the shift cancellation is evaluated. The actual Ne pressure in the cell is determined from the frequency shift of the 895-nm optical transition. We can then determine the Cs-Ne collisional temperature coefficients of the clock frequency. These results can be useful for vapor cell clocks and, particularly, for future microclocks.

A reference radiance-meter system for thermodynamic temperature measurements

The mise-en-pratique for the definition of the kelvin at high temperatures will formally allow dissemination of thermodynamic temperature either directly or mediated through high-temperature fixed points (HTFPs). In this paper, these two distinct dissemination methods are evaluated, namely source-based and detector-based. This was achieved by performing two distinct dissemination trials: one based on HTFPs, the other based on absolutely calibrated radiation thermometers or filter radiometers. These trials involved six national metrology institutes in Europe in the frame of the European Metrology Research Programme joint project ‘Implementing the new kelvin’ (InK). The results have shown that both dissemination routes are possible, with similar standard uncertainties of 1–2 K, over the range 1273–2773 K, showing that, depending on the facilities available in the laboratory, it will soon be possible to disseminate thermodynamic temperatures above 1273 K to users by either of the two methods with uncertainties comparable to the current temperature scale.

The Boltzmann project

Within the frame of a Raman-Ramsey CPT clock optimisation, we present our investigations on the coherence and population lifetime measurements in Cs vapour cells. To guarantee the reliability of the coherence lifetime measurements, three different methods are compared. Very good agreement is found between two of them and results are discussed for the third. In order to increase the coherence lifetime, two techniques are tested: Firstly a buffer gas can be added in the Cs vapour cell and secondly cell walls can be coated to reduce the destructive collisions against the walls. Buffer gas is tested first and then combined to a coating. First results are presented.

Calibration of Radiation Thermometers up to 3000\,^{\circ }\hbox {C}: Effective Emissivity of the Source

Recent progress are reported on a compact cesium cell atomic frequency standard based on pulsed Coherent Population Trapping interaction in the Dicke regime. Main short term and long term limiting parameters have been identified. Last improvements have permitted to reach a stability of 7×10⁻¹³ at 1sec and 2×10⁻¹⁴ at 2000 s. The noise characterization process is presented in this article.