Abstract
Electromagnetically induced transparency (EIT) and Autler–Townes splitting (ATS) originating from multilevel atomic systems have similar transparency windows in transmission spectra which causes confusion when discriminating between them, despite the difference in their physical mechanisms. Indeed, Fano interference is involved in EIT but not in ATS. There has been significant interest in the classic analogues of EIT and ATS in recent years, such as in photonics, plasmonics, optomechanics; however, the acoustic analogue of ATS has been rarely studied. In this work, we propose to investigate these phenomena in a pillared metasurface consisting of two lines of pillars on top of a thin plate. The existence of Fabry–Pérot resonance and the intrinsic resonances of the two lines of pillars act as a three-level atomic system that gives rise to the acoustic analogue of EIT and ATS. Since the frequency of Fabry–Pérot resonance can be tuned by controlling the distance between the two lines, the underlying physics, whether Fano interference is involved or not, is quite clear in order to discriminate between them. The realizations of EIT and ATS are put forward to control elastic waves for potential applications such as sensing, imaging, filtering.
Highlights
Phononic crystals[1,2,3,4,5,6] and acoustic metamaterials[7,8,9,10] are artificial acoustic composite materials controlling elastic/acoustic wave in novel ways and receiving large amounts of attention in broad communities
Phononic crystals possess Bragg band gaps resulting from the destructive interference among the inclusions/scatters when working wavelength is in the order of the lattice parameter, with applications like wave guiding[11,12,13], filtering[14,15,16], acoustic lensing[17,18,19] and so on; acoustic metamaterials exhibit hybridization band gaps resulting from local resonances at a larger wavelength and generate negative effective density or/and bulk modulus for negative refraction and super-resolution imaging[20, 21], cloaking[22,23,24] among others
Electromagnetically induced transparency (EIT) refers to the quantum interference of excitation with a three-level atomic system where a narrow transparency windows appears in an opaque region
Summary
Phononic crystals[1,2,3,4,5,6] and acoustic metamaterials[7,8,9,10] are artificial acoustic composite materials controlling elastic/acoustic wave in novel ways and receiving large amounts of attention in broad communities. Fano resonances were used to describe asymmetries in the autoionization spectra in atoms, named after the physicist Ugo Fano who firstly explained it in theory as the interference between individual resonances in the continuum[42] They are related to electromagnetically induced transparency (EIT)[43, 44] that needs a discrete transition coupled to a continuum, giving rise to a transparency window in the absorption/transmission spectrum. Several methods[62,63,64,65] are proposed to discriminate between them based on observed absorption or transmission spectra, but not on the physical mechanism behind (such as whether Fano resonance is involved or not) In another classic aspect, acoustic system, Fano resonance and EIT are investigated in several different structures[66,67,68,69,70]; the acoustic analogue of ATS has been rarely reported. Like the wide applications in optics or other systems, the realization of EIT and ATS in this work puts forward the control of elastic waves for potential applications such as sensing, imaging, filtering, among others, in micro or nano scale
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