Atomic clock based on a coherent population trapping resonance in 87Rb with improved high-frequency modulation parameters

This work reports for the first time development and experimental study of a laboratory prototype of an atomic clock with stability of 2x10(-11)tau(-1/2) (Allan deviation) over time 1 s < tau < 1000 s (7x10(-13) over 1000 s) on the basis of a coherent population trapping (CPT) resonance in Rb-87 in a compact spherical cell having 1.3-cm diameter and without any buffer gas. Demonstrated are dependencies of the width of the studied CPT resonance upon the amplitude and modulation frequency of optical frequency difference (3.417 GHz) of a bichromatic circularly polarised pump field. For the first time, a considerable non-linearity was discovered in the dependence upon the reference difference frequency of the spectral position of the CPT resonance when the modulation frequency of the optical frequency difference is varied within a broad range.