Electromagnetically induced waveguiding in double-A systems

Near the threshold for electromagnetically-induced transparency (EIT) or coherent population trapping (CPT), two-photon-resonance-enhanced self-focusing of a A system can be exploited to induce spatial confinement in a second, diffracting A system [1]. The diffracting A system is characterized by parameters below the EIT or CPT threshold, and the two A systems must be coupled to form a closed-loop double-A system (see Fig. 1). The waveguiding effect is shown to be strongly phase dependent, indicating that it derives from the phase-dependent effective third-order susceptibility rather than the phase-independent effective first-order susceptibility, as is the case in previously studied systems. We also show that when the second A system initially involves only a single laser beam, the loop is completed by the efficient generation of radiation at the four-wave mixing frequency, within a propagation distance much shorter than the diffraction length. As shown in Fig. 2, both the applied (V′₃₂, V′₃₂, V′₄₂) and generated (V′₄₁) fields exhibit electromagnetically-induced waveguiding.