Abstract
The introduction of single-pixel imaging and compressed sensing (CS) techniques into terahertz (THz) imaging has sped up image acquisition and avoided raster scanning. At present, most single-pixel terahertz imaging developments are based on simple metal samples, researchers rarely study the reconstruction of complex structural samples with large attenuation in the terahertz domain, such as metasurface holographic images. Here, we present an implementation of the single-pixel compressed sensing approach into THz metasurface holography reconstruction. By laser projecting a set of binary patterns on a 500-μm thick silicon wafer using a digital micromirror device (DMD), THz wavefront of the holographic metasurface is spatially encoded. Single-element detector is used to measure electric field amplitude of the transmitted THz radiation for each pattern, and then the hologram is reconstructed by Total variation Augmented Lagrangian and Alternating Direction Algorithm (TVAL3). Besides, the reconstruction effects are also analyzed by reducing measurement number, it can maintain more than 95% of the image information under 20% compression. The demonstrated combination of terahertz holography and single-pixel compressed sensing imaging provides new possibilities for metasurface imaging, verifies the stability of terahertz single-pixel imaging, and the scheme may lead to advances in fast terahertz imaging.
Highlights
Holography, a revolutionary three-dimensional imaging technique, has continuously aroused tremendous curiosity since the time it was originally proposed by Gabor in 1948 [1], Later in 1967 [2], computer-generated holography (CGH) emerged, and has been widely accepted because the holograms are created by numerical calculation and reconstructed optically, eliminating the need for real objects and highly temporal-spatial coherent light sources
Metasurfaces [3] have been used as holograms in CGH, compared with conventional SLMS, metasurfaces control the light on a sub-wavelength scale [4]–[7], and can produce high-efficiency meta-holography [8]–[10]
To realize the 3D large depth of focus (DOF) meta-hologram, dielectric cubic silicon resonators are employed as basic unit cells, as shown in Fig. 1(b), where P represents the periodic size of the unit cell, a, b, h represents the width, length, thickness of the silicon pillar, respectively, and θ represents the rotation angle of the silicon pillar
Summary
Holography, a revolutionary three-dimensional imaging technique, has continuously aroused tremendous curiosity since the time it was originally proposed by Gabor in 1948 [1], Later in 1967 [2], computer-generated holography (CGH) emerged, and has been widely accepted because the holograms are created by numerical calculation and reconstructed optically, eliminating the need for real objects and highly temporal-spatial coherent light sources. NSTM system has high spatial resolution while the scanning probe is fragile and damaged, and the weak signals emitting from the probe are very sensitive to noise, so the signal-to-noise ratio (SNR) of the reconstructed image is low, the NSTM system needs to scan sample surface point by point, and the measurement time is long. These are urgent problems to be solved in metasurface holograms characterization
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