Coherent Perfect Absorbers: Time-reversed Lasers

TL;DR

This paper demonstrates that arbitrary objects can be made perfectly absorbing at specific frequencies by adding dissipation and using coherent illumination, effectively reversing the lasing process and enabling new optical control devices.

Contribution

It introduces the concept of coherent perfect absorbers as the time-reversed counterpart of lasers, with a practical demonstration in silicon slabs.

Findings

Perfect absorption achieved at discrete frequencies

Absorption linked to zeroes of the S-matrix on the real axis

Potential applications in controlled optical energy transfer

Abstract

We show that an arbitrary body or aggregate can be made perfectly absorbing at discrete frequencies if a precise amount of dissipation is added under specific conditions of coherent monochromatic illumination. This effect arises from the interaction of optical absorption and wave interference, and corresponds to moving a zero of the elastic S-matrix onto the real wavevector axis. It is thus the time-reversed process of lasing at threshold. The effect is demonstrated in a simple Si slab geometry illuminated in the 500-900 nm range. Coherent perfect absorbers are novel linear optical elements, absorptive interferometers, which may be useful for controlled optical energy transfer.