Pseudoresonance mechanism of all-optical frequency standard operation
  We propose a novel approach to all-optical frequency standard design, based on a counterintuitive combination of the coherent population trapping effect and signal discrimination at the maximum of absorption for the probe radiation. The short-term stability of such a standard can achieve the level of 10^-14/(\tau)^1/2. The physics beyond this approach is dark resonance splitting caused by interaction of the nuclear magnetic moment with the external magnetic field. 
G. Kazakov, B. Matisov, I.Mazets, G.Mileti, J.Delporte