Study of lin ‖ lin CPT for application in vapour cell atomic

1 Abstract We evaluate the use of Coherent Population Trapping (CPT) excited with parallely polarized laser fields in vapour cell atomic clocks. We study the resonance shape, the discriminator slope and signal-to-noise ratio as a function of relevant parameters such as the laser frequency detuning and the applied magnetic field. We show that a stability of 6 · 10 −12 τ −1/2 may be reached in a compact system using a modulated VCSEL. Contrarily to the microwave-optical double resonance scheme, Coherent Population Trapping (CPT) does not require a microwave cavity, which may be an advantage in compact or miniature atomic clocks [1, 2]. CPT usually suffers from smaller signal contrast, even though different techniques have been recently proposed to overcome this potential limitation [3-6]. In this communication we present our study on the use of CPT in vapour cell frequency standards. We have investigated the case of 87 Rb D 1 when a longitudinal magnetic field is applied and the CPT is excited by a linearly polarized, unidirectional and multi-frequency light field (the so called linlin CPT) [7-10]. Here below the experimental setup is shortly described. In section two we present the signal shape for different values of magnetic field and we discuss the maximum contrast achievable in our configuration. In section three, the role of the laser frequency detuning, the noise measurements and determination of the optimal lock-in detection frequency are discussed. Finally, we predict the achievable clock frequency stability, basing our considerations on the presented signal-to-noise measurements.