Abstract-Analytical method for the diffraction of an electromagnetic wave by subwavelength graphene ribbons

 

Mahdi Rahmanzadeh, Amin Khavasi, and Behzad Rejaei

https://www.osapublishing.org/josab/abstract.cfm?uri=josab-38-3-953

Theoretical study of arrays of graphene ribbons is currently of high interest due to its potential application in beam splitters, absorbers, and polarizers. In this paper, an analytical method is presented for diffraction analysis of graphene ribbon arrays. Previous analytical studies were carried out in the regime where the lateral separation between the ribbons is much smaller than the wavelength of the incident wave. As such, they cannot be used to calculate the reflection coefficients of higher diffracted orders. In contrast, the method proposed here can predict the electromagnetic response of graphene ribbon arrays even when the array constant is larger than the wavelength. To reach our results, we first derive an analytical expression for the surface density of the electric current induced on the ribbons by an incident, transverse-magnetic, plane wave. Next, closed-form and analytical expressions are obtained for the reflection coefficients of the zeroth and higher diffracted orders. The results are in excellent agreement with those obtained from full-wave simulations. The method presented facilitates the design of tunable gratings with many potential applications in the terahertz regime and optics.

© 2021 Optical Society of America

Abstract-Terahertz lensing effect in high-temperature superconductors

Amirparsa Zivari, Mohammad Reza Tavakol, Amin Khavasi, Behzad Rejaei, 

https://www.osapublishing.org/josab/abstract.cfm?uri=josab-36-5-1241

We show that high-temperature superconductors can be used to build a terahertz superlens. These materials exhibit hyperbolic behavior at frequencies between their two plasma frequencies corresponding to electric fields parallel and perpendicular to their c-axis. Due to the large component of permittivity perpendicular to the c-axis, the resolution of the proposed lens is much below the diffraction limit (

𝜆/1000$\lambda /1000$). In this paper we demonstrate this lensing phenomenon with a simple slab of a high-temperature superconductor.

© 2019 Optical Society of America

Abstract- Design of mid-infrared ultra-wideband metallic absorber based on circuit

• Kamalodin Arik
• Sajjad Abdollahramezani
• Saeed Farajollahi
• Amin Khavasi
• Behzad Rejaei

http://www.sciencedirect.com/science/article/pii/S0030401816306046

An ultra-broadband absorber of light is proposed by using periodic array of ultra-thin metallic ribbons on top of a lossless quarter-wavelength dielectric spacer placed on a metallic reflector. We propose a fully analytical circuit model for the structure, and then the absorber is duly designed based on the impedance matching concept. As a result, normalized bandwidth of 99.5% is realized by the proposed absorbing structure in mid-infrared regime. Performing a numerical optimization algorithm, we could also reach to normalized bandwidth of 103%.