Coherent Perfect Absorption using Gaussian beams

Coherent perfect absorption (CPA) is theoretically studied for the realistic case of Gaussian laser light illumination on a metal-dielectric composite medium (CM). Two identical Gaussian beams are focused on two interfaces of the CM of orthorhombic shaped slab from opposite sides at equal angle of incidence. Here I deduce the essential conditions required for CPA and show that perfect CPA could be possible with Gaussian beams for both oblique and normal incidences. On the other hand, for oblique incidence perfect plane wave type CPA is observed for broad Gaussian beams since they fulfil the paraxial approximation whereas narrower beam exhibit slightly imperfect CPA (owing to reduced absorption) in the region away from axis. The critical dependence of CPA is observed with respect to small variations in various beam and CM parameters such as beam waist, angle of incidence, wavelength of incident beams, thickness and volume fraction of CM slab, which is attributed to experimental limitations. Farther, for normal incidence identical absorption profiles have been observed for different beam widths, whereas, for oblique incident profiles have less absorption for narrower beams.