Frequency Stability Measurement of a Raman-Ramsey Cs Clock

CPT clocks are studied worldwide as miniature frequency standards for portable applications. To improve their frequency stability, we have investigated the optimum operating conditions (cell temperature, laser intensity, interrogation method) and measured the corresponding frequency shifts and stability. Compared to the continuous CPT interrogation, the pulsed interrogation reduces the light shift by a factor 300 and improves the frequency stability by a factor 10. The short term frequency stability is 9 x 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> at 1 s, limited to 2 x 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> after 300 s.