Coherent population trapping with cold atoms

Atomic clocks based on CPT are interesting because of the narrow linewidths achievable at very low intensities. The linewidth of a CPT resonance in a sample of cold atoms mainly depends on the optical saturation by two lasers and the different relaxation terms responsible for destroying the hyperfine coherence. We propose a complete analytical solution for the excited population based on the classical Bloch formalism to determine the line shape of the resonance. Finally we present the future development of a cold atoms clock based on CPT linewidth.