Critical coupling to anti-lasers

Coherent perfect absorbers or anti-lasers are time reversed counterpart of lasers near threshold. The time reversed operation corresponds to the case when an absorber (instead of the amplifying active medium) in a cavity absorbs all the incident coherent light. Sub- and super- scattering in such systems has recently been demonstrated experimentally. We show that the concept of much-hyped anti-lasers is easily accessible to any undergraduate physics student with moderate understanding of interference. Analogous concepts were earlier used in critical coupling where all incident flux could be coupled to resonant structures with null scattering. In layman's term this implies complete absorption of the incident energy, while the structure neither reflects nor transmits.  We present the recent developments on perfect absorption charting out the route from critical coupling to anti-lasers. We stress the role of destructive interference in the underlying process of coherent perfect absorption leading to simultaneously null reflection and transmission. We also present new results on CPA using metal-dielectric nano-composites and other plasmonic structures. Note that metal nano-composites offer flexible optical response depending on the volume fraction of the metal inclusions. Moreover, they offer the possibility of excitation of localized plasmons with very large local field enhancements.