Ultrabroadband perfect imaging in terahertz wire media using single-cycle pulses

Abstract

Slabs formed by wire medium metamaterials are capable of transmitting evanescent waves over several wavelengths, and enable perfect imaging of field patterns with deeply subwavelength features over such long distances. To date, perfect imaging has been limited to narrow frequency windows defined by the Fabry–Perot (FP) resonance condition. Away from such resonances, backreflections within the slab result in the excitation of surface waves supported by the wire medium. This leads to image distortions, thus severely limiting the use of wire media for broadband subwavelength imaging. Here, we propose and demonstrate that this limitation can be overcome by using ultrashort electromagnetic pulses as the field source, allowing separation of the initial pulse from subsequent backreflections, which cannot be achieved using continuous-wave sources. Using a terahertz (THz) near-field microscope based on a time-domain approach, we demonstrate ultrabroadband transmission of distortion-free images over the entire frequency band of the source (0.1–1.75 THz). Such performance requires the slabs to be sufficiently long; the limits of this approach are also demonstrated by imaging a resonant mode with high Q-factor through a short slab. Our results pave the way for the implementation of wire media in broadband imaging applications based on short electromagnetic pulses, such as THz pulse imaging or optical imaging with ultrashort laser pulses.