We study the photonic properties of a one-dimensional periodic macroscopic ensemble of cold atoms. A large number of atoms is trapped in a 1D optical lattice, thus forming layers of disordered atomic pancakes. This induces a periodic modulation of the refractive index, which can yield a large Bragg reflection . In the past, adding four-wave mixing or EIT allowed us to obtain mirrorless optical parametric oscillation  and a two-port all-optical switch .
I will summarize these past results, which are all steady-state experiments. Now, we are studying temporal dynamical effects, in particular the optical transients in the Bragg reflection. I will show preliminary data on the existence of a small "flash" effect  in the Bragg reflection at the switch-off of the incident beam, and on the superradiant rate of the decay.
Finally, I will briefly discuss research prospects on this system: pulse propagation (slow light, quantum memory), spontaneous emission in the band gap, nonlinear effects, etc.
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