Coherent perfect absorption in resonant materials

Abstract

Coherent perfect absorption (CPA) is an interferometric effect that guarantees full absorption in a lossy layer independently of its intrinsic losses. To date, it has been observed only at a single wavelength or over narrow bandwidths, whereupon wavelength-dependent absorption can be ignored. Here we produce CPA over a bandwidth of ∼60 nm in a 2 µm thick polymer film with a low-doping concentration of an organic laser dye. A planar cavity is designed with a spectral ‘dip’ to accommodate the dye resonant linewidth, and CPA is thus achieved even at its absorption edges. This approach allows realizing strong absorption in laser dyes—and resonant materials in general—independently of the intrinsic absorption levels, with a flat spectral profile and without suffering absorption quenching due to high doping levels.

Broadband Omni-resonant Coherent Perfect Absorption in Graphene

“…Our previous work on CPA using the configuration shown in Fig. 1(c) assumed 'distributed' absorption; that is, the single-pass absorption A results from a layer in which absorption extends uniformly over its thickness L [5,18,19,50]. This assumption no longer holds for 'localized' absorption (such as a 2D material like graphene or a metasurface).…”

“…First, optical absorption in any medium over a finite bandwidth is wavelength dependent A = A(λ). As such, the cavity mirrors are required to have a wavelength-dependent reflectivity R 1 (λ) = R 2 (λ) = 1 − A(λ) that counterbalances the dispersive absorption, which can be realized via aperiodic multilayer dielectric mirrors [18,19]. Therefore, CPA is in principle materials-agnostic.…”

“…Eliminating the need for counterpropagating fields in turn eliminates the restrictions on the relative amplitude and phase, thus making the arrangement amenable to broadband incoherent light. Indeed, we recently demonstrated CPA in an asymmetric cavity over a bandwidth of ∼ 60 nm utilizing a fluorescent dye [19], and over a full octave of bandwidth ∼ 800-1600 nm using 2-µm-thick poly-crystallince silicon layer [18].…”