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The Journal of Physical Chemistry

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

Rob Vreeker, Max Glasbeek, A. H. Zewail

Published Jan 1, 1989• 1 citation
Publisher

Abstract

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

DOI
10.1021/j100339a032

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New Journal of Physics•Jan 5, 2012•2 citations
In this paper we consider the coherences that are produced in a photon (or spin) locking experiment involving a molecular \ntwo-level system. New coherences, not anticipated from the Feynman-Vernon-Hellwarth representation, are predicted if \nthe transition is inhomogeneously broadened. The influence of duration, power, and phase of the driving and probe pulses \nin the locking experiment on the shape of the simulated echo responses is discussed in detail, and a comparison with experiments \nis made.
Stimulated photon echoes (three-pulse echoes) produced by broadband (incoherent) light pulses are discussed. A switching time corresponding to the reciprocal inhomogeneous width is predicted for the echo signal when the time interval between the first two time-overlapping, mutually coherent pulses is scanned across 0. The effect is demonstrated in an experiment performed with cesium vapor. A new method for fast sampling of atomic or molecular velocity distribution is proposed with potential applications to photodissociation and photofragmentation studies.
The first observation of optical rotary echoes, the optical analog of rotary spin echoes, is reported. Rotary echoes are produced in a quantum-mechanical two-level system which is driven resonantly (nutation effect) by a coherent field that suffers a sudden phase retardation. The initial nutation transient dephases, because of an inhomogeneity in either the driving field or the transition frequency of the sample, and then rephases to form an echo following the phase-shifting pulse. Hence, optical rotary and photon echoes are similar processes---the former being an interference in nutation and the latter an interference in free precession. Perturbative solutions of the Bloch equations are derived for the case where inhomogeneous dephasing arises from Doppler broadening and the Rabi frequency exceeds the homogeneous damping rate. Observations of the optical rotary echo in I2{\mathrm{I}}_{2}I2​ vapor are facilitated by the technique of laser frequency switching, which generates precise phase shifts in the optical field. The measurements corroborate detailed theoretical predictions.
Using on-demand coherence conversion via optical locking, a dynamic coherent control of the collective atom phase has been demonstrated for longer photon storage beyond the critical constraint of spin phase decay time, where the storage time can be extended up to hours in a rare-earth-doped solid. Coherent transient phenomena such as photon echoes have been investigated for frozen phase decay via coherent population transfer using a simple deshelving optical pulse pair. Unlike the rephasing halt applied to two-pulse photon echoes, where optical decoherence is accelerated by spin inhomogeneous broadening, a completely atom phase-locked coherence conversion has been observed in three-pulse photon echoes, resulting in spin dephasing-free coherence control. Here, the mechanism of the atom phase-locked coherence conversion via optical locking has been investigated in a solid medium whose optical transition is imperfect, where partial coherence is lost via optical depth-dependent imperfect population transfer. The relationship between coherence loss and optical depth is analyzed, where nearly perfect photon echo efficiency can be obtained for ultralong photon storage in an optically thick medium.