The research findings are published in the Optics Letters (Q1; IF: 3,1).
Photonic jet in the terahertz (THz) frequency range, terajet, plays an important role in modern scanning systems to achieve a superresolution beyond the diffraction limit. In the microwave and THz frequency ranges, dielectric losses are five to seven times higher compared to the optical range, and their refractive index is normally higher than two. However, it is known that the resolution of existing technologies can be enhanced through the so-called terajet effect.
Currently, there are several methods for controlling and tuning the intensity, shape, and size of a photonic jet in the THz range. However, in most cases, the parameters of the generated terajet, such as the maximum field enhancement, effective length, and focal position, are determined by the permanent properties of the dielectric material. This complicates real-time tuning of these parameters, thus considerably limiting the potential use of terajets in THz imaging systems.
Researchers from the TPU School of Non-Destructive Testing together with their colleagues from Belarusian State University have developed an effective method of controlling the electromagnetic field of high index dielectrics. They first proposed using graphene to generate a photonic jet in the terahertz range and to tune its properties.
In their study, the scientists deposited a monolayer of graphene on the surface of a dielectric sphere. Then, they studied the process of interaction between a dielectric particle and graphene through computer modeling.
“The optical properties of graphene vary depending on the external potential. In addition, it is very flexible, so it can be used to create complex structures with desired properties and controllable spectral response. The study has shown that a certain external potential of graphene deposited on a dielectric sphere triggers a Fano resonance when the fields inside the sphere are highly amplified. As a result, the field in the terajet locus also increases to equal and in some cases exceeds the field for a dielectric with a refractive index of less than two. This effect ensures real-time control of the power and size of the generated terajet,” explains Igor Minin, professor at the Division for Electronic Engineering of the School of Non-Destructive Testing.
In their study, the scientists showed the property of graphene to facilitate the terajet formation by high index dielectrics. This proves the significant advantage of using a graphene-coated dielectric sphere, as compared to a homogeneous sphere, for dynamic control and tuning of terajet parameters. These findings can significantly contribute to the development of tunable THz imaging systems and other related applications.