We study the absorption and dispersion properties of a \Lambda-type atom embeded in a photonic crystal [1], with one transition spontaneously decaying within a band gap. Assuming an isotropic dispersion relation near the two band edges, we show that the (otherwise opaque) \Lambda-type medium can, in certain cases, become transparent to a probe laser pulse coupling to the other atomic transition [2,3]. We derive explicitly the dependence of the absorption profile on the width of the gap and also the transient behaviour of the system under conditions of transparency. Similar effects are already known to occur in the phenomenon of electromagnetically induced transparency [4], although in our case the effects are intrinsic to the system (due to "self-dressing" of the atom by its own localized radiation field), and not-laser induced.
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[3] D.G. Angelakis, E. Paspalakis and P.L. Knight, to appear in Phys. Rev. A, May 2000; E. Paspalakis, N. J. Kylstra and P.L. Knight, Phys. Rev. A 60, R33 (1999).
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