Low-Terahertz Transparent Graphene-Based Absorber

Abstract

A new, transparent, metal-free absorber, based on the use of multilayer graphene/dielectric laminates (GLs), is proposed for applications in the low-terahertz frequency range. The designed absorber has a total thickness of around 70 µm and consists of a front matching dielectric layer followed by a GL, a dielectric spacer and a back GL. The laminates are periodic structures constituted of graphene sheets separated by 50-nm-thick polyethylene terephthalate (PET) interlayers, while the matching layer and the spacer are one-quarter-wavelength thick and made of PET. The GLs are modeled as homogeneous-equivalent single layers (ESLs) characterized by their sheet resistances Rs. An innovative analytical method is proposed in order to select Rs values optimizing the electromagnetic wave absorption either in low-gigahertz or low-terahertz frequency range. The frequency spectra of the absorption, reflection and transmission coefficients are computed in the range up to 4 THz by using different values of Rs. Then, realistic Rs values of chemically doped graphene monolayers over PET substrates are considered. The designed absorbers are characterized by an absorption coefficient with a peak value of about 0.8 at the first resonant frequency of 1.1 THz, and a 1.4 THz bandwidth centered at 1.5 THz with reflection coefficient below - 10 dB. Moreover, the optical transmittance of the proposed absorbers are computed by means of the optical matrix theory and it is found to be greater than 86% in all the visible ranges.

Terahertz characterization of graphene conductivity via time-domain reflection spectroscopy on metal-backed dielectric substrates

“…where θ i is the angle of incidence (a nominal value of θ i = 8 • is provided by the manufacturer [40]), ∆τ := t ref − t 0 , and n avg,0 = c 0 ∆τ ′ /(2d), with ∆τ ′ := t 1 − t 0 , is the average refraction index for normal incidence (i.e., n avg,0 := n avg | θ i =0 ). Application of ( 1) and ( 2) to the results in figure 3 yields d ≃ 356 µm and n avg ≃ 1.73, which are both consistent with the expected values: the nominal thickness of this Mylar sample was 350 µm, whereas its average refractive index is consistent with data found in the literature [44]. In order to have a more accurate material characterization of the Mylar substrate, which also takes into account losses and frequency dispersion, we developed an equivalent circuit model to derive a theoretical reflection coefficient R th :…”

“…In order to find the best characterization for the Mylar we employed the Havriliak-Negami variation of the Debye model [44,45] (a time-harmonic e −jωt dependence is tacitly assumed):…”

A Polarization-Insensitive and Wide-Angle Terahertz Absorber with Ring-Porous Patterned Graphene Metasurface

“…Due to the strong localized surface plasmon resonance of the patterned graphene structure, most of the electric field was limited to the edge of the ring-shaped graphene, and part of the electric field was distributed inside the ring for both polarizations. This phenomenon is caused by strong electric dipole resonance, which can effectively capture the energy of light, and it shows that strong electric field confinement will lead to higher absorption [ 41 ]. Because the proposed absorber has symmetry, the electric field amplitude distribution of TE polarization is the same as that of TM polarization electric field after 90° rotation, which corresponds to the same absorption spectrum of TE and TM polarization.…”

Tunable Terahertz Perfect Absorber and Polarizer Based on one-Dimensional Anisotropic Graphene Photonic Crystal

“…Digital Object Identifier 10.1109/JPHOT.2022.3178163 low ohmic loss, adjustable Fermi level, and low absorption loss in the terahertz and far infrared (IR) [12], [13]. One-atom-thick graphene with a 2D honeycomb lattice absorbs 2.3% of light in the mentioned frequency ranges.…”