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 report polarization-controlled emission from an emitter stack that consists of two spintronic Fe/Pt terahertz emitters. Since the magnetization in the thin iron film of both emitters stays aligned with the easy magnetization axis after removal of an external magnetic bias field, the polarization of the emitted fields from both emitters can be independently controlled by rotation of the two emitters relative to each other. We studied the dependence of the amplitude and polarization of the emitted terahertz field from the stack on the relative rotation of the emitters and the gap width between the emitters in the stack.
We analytically and experimentally investigate the radiated terahertz fields from a stack of two spintronic Fe/Pt terahertz emitters that are aligned back to back with the Pt-surfaces facing each other. We experimentally and theoretically study the dependence of the emitted terahertz fields from the stack on the relative orientation of the individual emitters. For collinear alignment in the same direction, we determined an increase of the maximal emission amplitude by a factor of 1.57 in comparison with a single emitter. We also evaluated the cavity effects that originate from the air gap between the individual emitters in theory and experiment.
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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