Terahertz single pixel imaging with frequency-multiplexed metasurface modulation

Single-pixel imaging is a very attractive technique at the terahertz band due to the lack of mature array detectors, over which the spatial light modulator is the most crucial component. Metasurfaces are usually introduced into the modulator to enhance the modulation depth of active materials. Here we take advantage of the flexible spectral response of pixelated metasurface resonators to encode different spatial masks into different frequency windows, without active materials and external stimuli. The measurements are obtained in parallel as opposed to in sequence in the time-domain spectroscopy system through a single terahertz signal. Images with 2 x 2 pixels as proof of the concept are reconstructed with high fidelity and plenty of choices of the frequency windows. As the measurement time does not increase with the number of pixels, this scheme can be generalized for imaging with higher resolution and increased number of pixels for practical applications in noninvasive inspection and detection.