Study of lin||lin CPT for application in vapour cell atomic clocks

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 $6\cdot {10}^{-12}$ ${\tau }^{-1\mathrm{/}2}$ may be reached in a compact system using a modulated VCSEL.