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Joint Conference of the European Frequency and Time Forum and IEEE International Frequency Control Symposium (EFTF/IFCS)

Spectroscopy and hyperfine clock frequency shift measurements in Cs vapor cells coated with octadecyltrichlorosilanes (OTS)

Moustafa Abdel Hafiz, Vincent N. Maurice, Ravinder Chutani, Nicolas Passilly, Christophe Gorecki, Stéphane Guérandel, Emeric de Clercq, Rodolphe Boudot

Published Apr 1, 2015• 0 citations
Publisher

Abstract

We report the characterization using coherent population trapping (CPT) spectroscopy of an octadecyltrichlorosilane (OTS)-coated centimeter-scale Cs vapor cell. The linewidth of the narrow CPT resonance is compared to the linewidth of an evacuated Cs cell of similar size. The Cs-OTS adsorption energy is measured to be (0.42 ± 0.03) eV. A hyperfine population lifetime, T1of 1.6 ms is reported, corresponding to about 37 useful bounces. Ramsey CPT fringes are detected using a pulsed CPT interrogation scheme.

DOI
10.1109/fcs.2015.7138787

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We report the characterization using coherent population trapping (CPT) spectroscopy of an octadecyltrichlorosilane (OTS)-coated centimeter-scale Cs vapor cell. The linewidth of the narrow CPT resonance is compared to the linewidth of an evacuated Cs cell of similar size. The Cs-OTS adsorption energy is measured to be (0.42 ± 0.03) eV. A hyperfine population lifetime, T1of 1.6 ms is reported, corresponding to about 37 useful bounces. Ramsey CPT fringes are detected using a pulsed CPT interrogation scheme.
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 ± 0.03) eV, leading to a clock frequency shift rate of 2.7 × 10−9/K in fractional unit. A hyperfine population lifetime, T1, and a microwave coherence lifetime, T2, 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.
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 ±\pm± 0.03) eV, leading to a clock frequency shift rate of 2.7×10−9/2.7\times10^{-9}/2.7×10−9/K in fractional unit. A hyperfine population lifetime, T1T_1T1​, and a microwave coherence lifetime, T2T_2T2​, 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.
Pulsed coherent population trapping (CPT) spectroscopy is applied in buffer-gas filled Cs–Ne vapor microfabricated cells. The properties of the Ramsey-CPT clock transition central fringe (linewidth, signal amplitude, and contrast) are studied versus several experimental parameters, including the Ramsey sequence and the input laser intensity, and are compared to those obtained in the conventional continuous (CW) interrogation mode. In the pulsed case and for short Ramsey-free evolution times TR, the central fringe linewidth is found to exhibit a small but visible power broadening and is measured to be narrower than the value of 1/(2TR) that is reached for long TR. The microwave hyperfine coherence lifetime T2 in the Cs–Ne microcells is measured to be in the 50–500 μs range. Its dependence to the buffer gas pressure or cell temperature is briefly studied.
We report on the detection of high-contrast and narrow Coherent Population Trapping (CPT) Ramsey fringes in a Cs vapor cell using a simple-architecture laser system. The latter allows the combination of push-pull optical pumping (PPOP) and a temporal Ramsey-like pulsed interrogation. An originality of the optics package is the use of a single Mach-Zehnder electro-optic modulator (MZ EOM) both for optical sidebands generation and light switch for pulsed interaction. Typical Ramsey fringes with a linewidth of 166 Hz and a contrast of 33 % are detected in a cm-scale buffer-gas filled Cs vapor cell. This technique could be interesting for the development of high-performance and low power consumption compact vapor cell clocks based on CPT.
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.
This article reports on the development and short-term fractional frequency stability of a continuous-regime (CW) Cs vapor cell atomic clock based on coherent population trapping (CPT). The push-pull optical pumping technique is used to increase the number of atoms that participate to the clock transition, yielding a typical CPT resonance contrast of 25% for a CPT linewidth of about 450 Hz. The clock short-term fractional frequency stability is measured to be 3 x 10 -13 τ -1/2 up to 100 seconds averaging time, in correct agreement with the signal-to-noise ratio limit. The mid-term frequency stability results are currently mainly limited by laser power effects. The detection of high-contrast narrow Raman-Ramsey fringes is demonstrated with this setup by making the atoms interact with a light pulse sequence.