08 Fakultät Mathematik und Physik

Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/9

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    High space‐bandwidth‐product (SBP) hologram carriers toward photorealistic 3D holography
    (2024) Li, Jin; Li, Xiaoxun; Huang, Xiangyu; Kaissner, Robin; Neubrech, Frank; Sun, Shuo; Liu, Na
    3D holography capable of reproducing all necessary visual cues is considered the most promising route to present photorealistic 3D images. Three elements involving computer‐generated hologram (CGH) algorithms, hologram carriers, and optical systems are prerequisites to create high‐quality holographic displays for photorealistic 3D holography. Especially, the hologram carrier directly determines the holographic display capability and the design of high space‐bandwidth‐product (SBP) optical systems. Currently, two categories of hologram carriers, i.e., spatial light modulators (SLM) and metasurfaces, are regarded as promising candidates for photorealistic 3D holography. However, most of their SBP capability still cannot match the amount of information generated by the CGH. To address this issue, tremendous efforts are made to improve the capability of hologram carriers. Here, the main hologram carriers (from SLM to metasurfaces) that are widely utilized in holography systems to achieve high SBP capability (high resolution, wide viewing angles, and large sizes) are reviewed. The purpose of this review is to identify the key challenges and future directions of SLM‐based and metasurface‐based holography for photorealistic 3D holographic images.
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    Generation of terahertz radiation via the transverse thermoelectric effect
    (2023) Yordanov, Petar; Priessnitz, Tim; Kim, Min‐Jae; Cristiani, Georg; Logvenov, Gennady; Keimer, Bernhard; Kaiser, Stefan
    Terahertz (THz) radiation is a powerful tool with widespread applications ranging from imaging, sensing, and broadband communications to spectroscopy and nonlinear control of materials. Future progress in THz technology depends on the development of efficient, structurally simple THz emitters that can be implemented in advanced miniaturized devices. Here, it is shown how the natural electronic anisotropy of layered conducting transition metal oxides enables the generation of intense terahertz radiation via the transverse thermoelectric effect. In thin films grown on off‐cut substrates, femtosecond laser pulses generate ultrafast out‐of‐plane temperature gradients, which in turn launch in‐plane thermoelectric currents, thus allowing efficient emission of the resulting THz field out of the film structure. This scheme is demonstrated in experiments on thin films of the layered metals PdCoO2 and La1.84Sr0.16CuO4, and model calculations that elucidate the influence of the material parameters on the intensity and spectral characteristics of the emitted THz field are presented. Due to its simplicity, the method opens up a promising avenue for the development of highly versatile THz sources and integrable emitter elements.
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    Wafer-scale self-organized InP nanopillars with controlled orientation for photovoltaic devices
    (2015) Sanatinia, Reza; Berrier, Audrey; Dhaka, Veer; Perros, Alexander P.; Huhtio, Teppo; Lipsanen, Harri; Anand, Srinivasan
    A unique wafer-scale self-organization process for generation of InP nanopillars is demonstrated, which is based on maskless ion-beam etching (IBE) of InP developed to obtain the nanopillars, where the height, shape, and orientation of the nanopillars can be varied by controlling the processing parameters. The fabricated InP nanopillars exhibit broadband suppression of the reflectance, ‘black InP,’ a property useful for solar cells. The realization of a conformal p-n junction for carrier collection, in the fabricated solar cells, is achieved by a metalorganic vapor phase epitaxy (MOVPE) overgrowth step on the fabricated pillars. The conformal overgrowth retains the broadband anti-reflection property of the InP nanopillars, indicating the feasibility of this technology for solar cells. Surface passivation of the formed InP nanopillars using sulfur-oleylamine solution resulted in improved solar-cell characteristics. An open-circuit voltage of 0.71 V and an increase of 0.13 V compared to the unpassivated device were achieved.
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    Electro-active metaobjective from metalenses-on-demand
    (2022) Karst, Julian; Lee, Yohan; Floess, Moritz; Ubl, Monika; Ludwigs, Sabine; Hentschel, Mario; Giessen, Harald
    Switchable metasurfaces can actively control the functionality of integrated metadevices with high efficiency and on ultra-small length scales. Such metadevices include active lenses, dynamic diffractive optical elements, or switchable holograms. Especially, for applications in emerging technologies such as AR (augmented reality) and VR (virtual reality) devices, sophisticated metaoptics with unique functionalities are crucially important. In particular, metaoptics which can be switched electrically on or off will allow to change the routing, focusing, or functionality in general of miniaturized optical components on demand. Here, we demonstrate metalenses-on-demand made from metallic polymer plasmonic nanoantennas which are electrically switchable at CMOS (complementary metal-oxide-semiconductor) compatible voltages of ±1 V. The nanoantennas exhibit plasmonic resonances which can be reversibly switched ON and OFF via the applied voltage, utilizing the optical metal-to-insulator transition of the metallic polymer. Ultimately, we realize an electro-active non-volatile multi-functional metaobjective composed of two metalenses, whose unique optical states can be set on demand. Overall, our work opens up the possibility for a new level of electro-optical elements for ultra-compact photonic integration.