Acoustic coherent perfect absorber and laser modes via the non-Hermitian dopant in the zero index metamaterials

Abstract

In this work, we propose a simple scheme to realize an acoustic coherent perfect absorber (CPA) and laser modes by embedding a non-Hermitian dopant in a zero index metamaterial. When the dopant is filled with a loss medium at a specific level, the sample can absorb the incident waves completely. On the other hand, when the dopant is filled with a gain medium, the sample can act as a laser oscillator to boost the incident waves. The theoretical derivation based on the scattering matrix and the numerical simulation based on the finite element method are performed and both show good agreement with each other. We also discover that the CPA and laser modes are very sensitive and can be controlled by adjusting the structure parameters or the relative phase of the incident waves. Moreover, the case that asymmetric incidences have different beam widths is considered. We envision that our work may have potential applications in designing acoustic devices, such as absorbers, transducers, and receivers.

Theory on coherent perfect absorber and laser via a metamaterial slab with complex parameters

“…Our theory provides an accurate guidance for both cases. Especially, in the latter case, it is shown that a medium with purely imaginary permittivity and permeability of opposite signs can realize CPA-laser, i.e., simultaneous CPA and laser at the same frequency, which is consistent with previous results [64][65][66][67][68][69][70][71]. Our work aims to provide a unified picture to design the parameters of a homogenous metamaterial slab that functions as CPAs, lasers or their coexistence.…”

“…Metasurfaces which feature the P T -symmetry have also been designed to achieve CPA, laser or their coexistence. However, coherent perfect absorption and lasing can also emerge in configurations without P T -symmetry [62,63], as well as a unique type of zero-index medium with both gain and loss [64][65][66][67], the pseudopassive media [68] or complex conjugate media [69][70][71][72][73], etc.…”

“…Generally, the medium with both complex permittivity and complex permeability in this case gives rise to complex refractive index, i.e., n = n + in (n = 0) and the loss or/and gain in parameters make it the ideal material to achieve CPA or laser. Exceptionally, the refractive index of this medium is real with a suitable combination of permittivity and permeability [64][65][66][67][68]. Just like the complex conjugate media [69][70][71][72][73], in which the ratio of the complex permittivity and the complex conjugate permeability is real, i.e., μ = αε * .…”

Coherent perfect absorber and laser induced by directional emissions in the non-Hermitian photonic crystals

“…In the PT-symmetric systems, the complex permittivity exhibits a symmetric spatial profile of ε(x) = ε * (−x) [25,26]. The scattering of electromagnetic waves by boundaries can produce CPA and laser effects [27]. When the amplitude and phase of the two incident waves are well-tuned (in-phase excitation), the outgoing waves will disappear, and the resulting may lead to perfect absorption.…”

Unidirectional Negative Refraction at an Exceptional Point of Acoustic PT-Symmetric Systems

“…After the extension from optics to acoustics, the progress in designing and realizing PT -symmetric acoustic systems has resulted in many nontrivial asymmetric effects such as unidirectional sound wave-vector manipulation, [31][32][33][34][35] unidirectional invisibility, [2,[36][37][38] and asymmetric reflection and diffraction. [39][40][41][42][43][44] Negative refraction as a special wave behavior has been realized by acoustic metamaterials where the effective density (𝜌) and bulk modulus (𝐵) are simultaneously negative. [45][46][47] It also enables new way of manipulating a sound field and plays an important role in a variety of applications, especially in acoustic focusing and imaging.…”