Abstract :
Summary form only given. In a three-level system, two resonant optical fields can excite spin coherence on the ground states via two-photon resonance. One of the two-superposition states created by the atom-field interactions is decoupled from the excited state. Thus, the population can be trapped in that state showing non-absorption resonance. The essential feature of this decoupled state is dark resonance. Therefore, the existence of the dark resonance is a basis of non-absorption resonance, coherent population trapping, and electromagnetically induced transparency. In a four-level system, however, the two-laser induced spin coherence can be broken when a third laser is applied. At the same time, new coherence between the third laser and one of the pre-existed lasers is created. This phenomenon is useful for optical switching owing to annihilation and creation of the dark resonance in the four-level system. It is noted that the switching time depends on the dark resonance build-up time, which is inversely proportional to the applied Rabi frequency. Numerical simulations are shown for potentially ultrahigh-speed optical switches. Each diffracted four-wave mixing signal is proportional to the spin coherence strength. For a preliminary experiment, a spectral hole-burning crystal is used. The intensity of the diffracted signals is reversed at line center. This coherence switching effect is based on the dark resonance interactions.
Keywords :
light coherence; multiwave mixing; optical hole burning; optical pumping; optical switches; quantum optics; self-induced transparency; applied Rabi frequency; atom-field interactions; coherence switching effect; coherent population trapping; dark resonance; diffracted four-wave mixing signal; electromagnetically induced transparency; four-level system; ground states; optical switching; quantum switching; resonance build-up time; resonant optical fields; spectral hole-burning crystal; spin coherence; three-level system; two-photon resonance; two-superposition states; ultrahigh-speed optical switches; Atom optics; Four-wave mixing; Frequency; Nonlinear optics; Numerical simulation; Optical diffraction; Optical mixing; Optical switches; Resonance; Stationary state;