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Articles you may be interested inA low phase noise microwave frequency synthesis for a high-performance cesium vapor cell atomic clock Rev. Sci. Instrum. 85, 094709 (2014); 10.1063/1.4896043 Exploring Ramsey-coherent population trapping atomic clock realized with pulsed microwave modulated laser J. Appl. Phys. 115, 093109 (2014); 10.1063/1.4867915 Quasi-bichromatic laser for a lin⊥lin coherent population trapping clock produced by vertical-cavity surfaceemitting lasers Rev. Sci. Instrum. 83, 093111 (2012);We report the characterization of dark line resonances observed in Cs vapor microcells filled with a unique neon ͑Ne͒ buffer gas. The impact on the coherent population trapping ͑CPT͒ resonance of some critical external parameters such as laser intensity, cell temperature, and microwave power is studied. We show the suppression of the first-order light shift by proper choice of the microwave power. The temperature dependence of the Cs ground state hyperfine resonance frequency is shown to be canceled in the 77-80°C range for various Ne buffer gas pressures. The necessity to adjust the Ne buffer gas pressure or the cell dimensions to optimize the CPT signal height at the frequency inversion temperature is pointed out. Based on such Cs-Ne microcells, we preliminary demonstrate a 852 nm vertical cavity surface emitted laser ͑VCSEL͒-modulated based CPT atomic clock exhibiting a short term fractional frequency instability y ͑͒ = 1.5ϫ 10 −10 −1/2 until 30 s. These results, similar to those published in the literature by others groups, prove the potential of our original microcell technology in view of the development of high-performance chip scale atomic clocks.

Presented is the observation of a quadratic temperature dependence of the Cs 0 -0 ground state hyperfine resonance frequency in a single Neon (Ne) buffer gas vapour microcell. The inversion temperature, expected to be theoretically independent of the buffer gas pressure, is measured to be about 808C for two different samples. A proposal to develop chip scale atomic clocks with improved long-term frequency stability, simpler configuration (a single buffer gas instead of a buffer gas mixture) and then relaxed constraints on pressure accuracy during the cell filling procedure is presented.Introduction: In the last decade, the significant advances in micromachining technologies and semiconductor lasers combined with the coherent population trapping phenomenon [1] has allowed the development of chip scale atomic clocks (CSAC) [2,3]. These miniature time references, exhibiting typical frequency stability of the order of 10 210 at 1 s and 10 211 at 1000 s to 1 day for a volume of a few tens of cm 3 and a power consumption of 150 mW, are of great interest in various portable battery-operated applications, such as navigation receivers and telecommunication systems.The heart of these miniature frequency standards usually consists of a microfabricated alkali vapour cell, formed in a wafer of silicon with glasses bonded to both sides. The cell is filled with buffer gases in order to prevent wall relaxation, increase the atom -light interaction time, and reduce the Doppler broadening [4]. Nevertheless, slight interactions taking place between alkali atoms and buffer gases cause a frequency shift of the hyperfine transition of the atom. This shift Dn, of the order of several hundreds of Hz per Torr, is expected to be dependent on the nature of the gas, pressure and operating temperature T, and can be expressed as in [5]:

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The wafer-level integration technique of PageWafer R (SAES Getters' solution for getter film integration into wafer to wafer bonded devices) has been tested in hermetically sealed miniature glass-Si-glass cells filled with Cs and Ne, e.g. for microelectromechanical systems (MEMS) atomic clock applications. Getter effects on the cell atmosphere are analyzed by quadruple mass spectroscopy and coherent population trapping (CPT) spectroscopy. The quadruple mass spectroscopy revealed that the residual gases (H 2 ,O 2 ,N 2 and CO 2 ) that are attributed to anodic bonding process are drastically reduced by the getter films while desirable gases such as Ne seem to remain unaffected. The impurity pressure in the getter-integrated cells was measured to be less than 4 × 10 −2 mbar, i.e. pressure 50 times lower than the one measured in the cells without getter (2 mbar). Consequently, the atmosphere of the getter-integrated cells is much more pure than that of the getter-free cells. CPT signals obtained from the getter-integrated cells are stable and are, in addition, similar to each other within a cell batch, suggesting the strong potential of applications of this getter film and especially for its wafer-level integration to MEMS atomic clocks and magnetometers.

This paper reports on an original architecture of microfabricated alkali vapor cell designed for miniature atomic clocks. The cell combines diffraction gratings with anisotropically etched single-crystalline silicon sidewalls to route a normally-incident beam in a cavity oriented along the substrate plane. Gratings have been specifically designed to diffract circularly polarized light in the first order, the latter having an angle of diffraction matching the (111) sidewalls orientation. Then, the length of the cavity where light interacts with alkali atoms can be extended. We demonstrate that a longer cell allows to reduce the beam diameter, while preserving the clock performances. As the cavity depth and the beam diameter are reduced, collimation can be performed in a tighter space. This solution relaxes the constraints on the device packaging and is suitable for wafer-level assembly. Several cells have been fabricated and characterized in a clock setup using coherent population trapping spectroscopy. The measured signals exhibit null power linewidths down to 2.23 kHz and high transmission contrasts up to 17%. A high contrast-to-linewidth ratio is found at a linewidth of 4.17 kHz and a contrast of 5.2% in a 7-mm-long cell despite a beam diameter reduced to 600 μm.

We report the realization and characterization using coherent population trapping (CPT) spectroscopy of an octadecyltrichlorosilane (OTS)-coated centimeter-scale Cs vapor cell. The dual-structure of the resonance lineshape, with presence of a narrow structure line at the top of a Doppler-broadened structure, is clearly observed. The linewidth of the narrow resonance is compared to the linewidth of an evacuated Cs cell and of a buffer gas Cs cell of similar size. The Cs-OTS adsorption energy is measured to be (0.42 6 0.03) eV, leading to a clock frequency shift rate of 2.7 Â 10 À9 /K in fractional unit. A hyperfine population lifetime, T 1 , and a microwave coherence lifetime, T 2 , of 1.6 and 0.5 ms are reported, corresponding to about 37 and 12 useful bounces, respectively. Atomic-motion induced Ramsey narrowing of dark resonances is observed in Cs-OTS cells by reducing the optical beam diameter. Ramsey CPT fringes are detected using a pulsed CPT interrogation scheme. Potential applications of the Cs-OTS cell to the development of a vapor cell atomic clock are discussed. V C 2015 AIP Publishing LLC. [http://dx.

International audienceThis paper describes a study of the thermal behaviour of fully packaged Caesium vapour cell developed in the framework of the European collaborative research project called "MEMS atomic clocks for timing, frequency control and communications (MAC-TFC)". This cell, along with various electronic and optical components, is embedded in a Low Temperature Co-fired Ceramics (LTCC) structure, in order to build a compact MEMS-based atomic clock. Functioning of such atomic clock depends on inner and outer environment of the Cs vapour cell, including parameters such as pressure and temperature of buffer gas. This paper is then devoted to study the thermal behaviour of a fully LTCC-packaged Cs vapour cell according to the ambient temperature change when it is locally temperature controlled. Simulations have been carried out by using analytical modelling and finite element based softwares. Different solutions concerning the LTCC structure such as bridges/suspensions, vacuum environment, metallic coating, as well as the optimal positions of the temperature-control elements have been investigated. Finally, preliminary experiments based on a prototype resulting from this study are presented and an additional solution based on the dynamic adjustment of the set temperature as a function of the ambient temperature is proposed