Abstract
The low-intensity absorption profile of a laser-driven two-state atom near the surface of a phase conjugator (PC) has been derived. The medium is assumed to be a nonlinear crystal in which the phase conjugation of a weak incident field is brought about by four-wave mixing with two strong pump beams. An atom near such a PC can excite and decay spontaneously because of the coupling of the atomic dipole to the electric field of the modified vacuum near the medium. In addition, the driving laser induces stimulated transitions between the two levels in the usual way. During the spontaneous transitions, resonance-fluorescence photons are emitted, and this radiation might be accessible for experimental observation. Then the predicted spontaneous excitations could be observed indirectly through their modifications of the spectral distribution of this radiation. A major experimental complication appears to be the large amount of stray light that is emitted spontaneously in all directions by the four-wave mixer (this light is essentially the transmitted and amplified vacuum field that is incident on the back port of the PC; for this reason, this radiation is sometimes called “quantum noise”). As an alternative, the probe absorption spectrum of the driven system could be measured. This profile is, like the fluorescence spectrum, influenced by the presence of the PC, and it carries similar information about the spontaneous transitions in the atom that are induced by the PC. This experiment is expected to be much less sensitive to the ubiquitously of the quantum noise since the probe beam can be directed along the surface of the medium and can be detected at a large distance from the crystal.
© 1993 Optical Society of America
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