A broadband multifocal metalens in the terahertz frequency range

• A metalens with adjustable number and arrangement of focal points in the terahertz range of frequency is proposed.
• Simultaneous phase and amplitude modulation of the incident light within a one-dimensional arrangement of metasurfaces is applied for designing the lens.
• The designed lens has a wide range of working frequency.

Metasurfaces, the 2D form of metamaterials with their ability in phase, amplitude and polarization manipulation are widely used in designing optical devices. Efforts to find proper photonic components in the terahertz (THz) range of frequency lead us to adopt metasurfaces as their constituent elements. Here, we conceived a broadband THz lens with an adjustable number and arrangement of focal points. To have a full control over the lens functionality, we used a metasurface with the capability of simultaneously modulating the amplitude and phase of the incident wave. C-shaped ring resonators (CSRRs) with different geometry and orientation capable of simultaneously manipulating phase and amplitude of the scattered fields, are proper choice to design the lens. We show that the introduced lens in a one-dimensional layout has a wide range of working frequencies within the THz spectrum, which can be used in a plethora of applications.