Controllable coherent perfect absorption in a composite film

We exploit the versatility provided by metal--dielectric composites to demonstrate controllable coherent perfect absorption (CPA) in a slab of heterogeneous medium. The slab is illuminated by coherent light from both sides, at the same angle of incidence and the conditions required for CPA are investigated as a function of the different geometrical parameters. The simultaneous realization of CPA at two distinct frequencies is also shown. Finally, our calculations clearly elucidate the role of absorption as a necessary prerequisite for CPA.