Light amplification and attenuation in stratified structures with a complex refractive index

We report a new kind of laser-threshold resonance in electromagnetic wave p ropagation inside a layered medium. Specifically, for large values of the g ain coefficient, the wave interaction with only the first few lattice inter faces results in transmission and reflection values of much greater than un ity. We also show that the duality phenomenon between losses and gains on t he field amplitude decay is due to the existence of counterpropagating wave s on reflection from the layer interfaces.