We use particle swarm algorithms to devise subwavelength waveguide array structures that serve, for example, as transmissive walls (transmittance > 88%) for microwaves with incidence angles between -80 and +80 deg or spatial filters that refract microwaves with incidence angles smaller than +/-20 deg at a refraction angle of 0 deg in the forward direction. Furthermore, we optimized radar cross section reducing (RCSR) metasurfaces by use of stimulated annealing and applied machine learning to implement an RIS, whose backward deflection angle of a normally incident wave is electrically tuned between 5 deg and 65 deg for microwaves at 31 GHz.
We present a terahertz-SLM with a frequency working range from 1.0 THz to 2.3 THz. Over the complete frequency range, the spatial modulation contrast exceeds 50% with a peak modulation contrast of 87% at 1.38 THz. The pixels of the SLM consist of mirror arrays that can be selectively actuated by a bias voltage of 35 V. Each individual pixel can either work as a grating, that diffracts terahertz radiation away from the detector, or as a flat mirror, that reflects all terahertz radiation into the detector. The mirrors have a size of 220 μm x 100 μm. Due to the wide frequency working bandwidth of more than 1 THz, such modulators can be used as spatial light modulators in terahertz coded aperture imaging spectroscopes with single-pixel detectors.
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