Photon locking and its observation by the probe-echo method: application to optical and microwave transitions

In this paper we consider the coherences that are produced in a photon (or spin) locking experiment involving a molecular two-level system. New coherences, not anticipated from the Feynman-Vernon-Hellwarth representation, are predicted if the transition is inhomogeneously broadened. The influence of duration, power, and phase of the driving and probe pulses in the locking experiment on the shape of the simulated echo responses is discussed in detail, and a comparison with experiments is made.