Hyperspectral imaging of microwave metasurfaces with deeply subwavelength resolution.

Electromagnetic metasurfaces offer a route to exotic, customised material properties that are not found in nature. However, in practice these artificial materials often do not live up to the promise of their design, limited by a myriad of fabrication challenges and defects. Global responses, such as transmission or reflection spectra, cannot distinguish different defect types, while scanning point measurements are impractical for materials which can contain thousands of individual meta-atoms. In this work we introduce a diagnostic imaging approach applicable to metasurfaces across the microwave, millimeter wave and THz bands, which we demonstrate with a microwave single-pixel camera. Using a near-field photomodulator, our approach can discern the resonance frequencies of individual meta-atoms in a complex microwave metasurface over large areas (80 x 80 mm), with spatial resolution far below the microwave wavelength (λ) and with capabilities beyond λ/600 at 15 GHz. We demonstrate high throughput visualisation of inhomogeneous broadening across various samples, while resolving near-field distributions of deeply subwavelength meta-atoms, and gaining valuable insight into the operational limitations of real-world metasurfaces.