Controllable photonic crystal with periodic Raman gain in a coherent atomic medium.

With two sets of standing-wave fields built in a thermal rubidium vapor cell, we have established a controllable photonic crystal with periodic gain in a coherently prepared N-type four-level atomic configuration. First, the photonic lattice constructed by a resonant standing-wave coupling field results in a spatially modulated susceptibility and makes the signal field diffract in a discrete manner under the condition of electromagnetically induced transparency. Then, with the addition of the standing-wave pump field, the N-type atomic medium can induce a periodic Raman gain on the signal field, which can be effectively controlled by tuning the pertinent atomic parameters. The experimental demonstration of such a real-time reconfigurable photonic crystal structure with periodic Raman gain can pave the way for realizing desired applications predicted in the gain-modulated periodic optical systems.