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Author: Grunwald, Ruediger × End date: 2022 × Start date: 2022 × End date: 2023 × Start date: 2020 × DDC: 600 × Type: Article × WGL Institute: MBI ×

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    Ultrashort vortex pulses with controlled spectral gouy rotation
    (Basel : MDPI, 2020) Liebmann, Max; Treffer, Alexander; Bock, Martin; Wallrabe, Ulrike; Grunwald, Ruediger
    Recently, the spatio-spectral propagation dynamic of ultrashort-pulsed vortex beams was demonstrated by 2D mapping of spectral moments. The rotation of characteristic anomalies, so-called "spectral eyes", was explained by wavelength-dependent Gouy phase shift. Controlling of this spectral rotation is essential for specific applications, e.g., communication and processing. Here, we report on advanced concepts for spectral rotational control and related first-proof-of-principle experiments. The speed of rotation of spectral eyes during propagation is shown to be essentially determined by angular and spectral parameters. The performance of fixed diffractive optical elements (DOE) and programmable liquid-crystal-on silicon spatial light modulators (LCoS-SLMs) that act as spiral phase gratings (SPG) or spiral phase plates (SPP) is compared. The approach is extended to radially chirped SPGs inducing axially variable angular velocity. The generation of time-dependent orbital angular momentum (self-torque) by superimposing multiple vortex pulses is proposed. © 2020 by the authors.
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    Micro Fresnel mirror array with individual mirror control
    (Bristol : IOP Publ., 2020) Poyyathuruthy Bruno, Binal; Schütze, Robert; Grunwald, Ruediger; Wallrabe, Ulrike
    We present the design and fabrication of a miniaturized array of piezoelectrically actuated high speed Fresnel mirrors with individual mirror control. These Fresnel mirrors can be used to generate propagation invariant and self-healing interference patterns. The mirrors are actuated using piezobimorph actuators, and the consequent change of the tilting angle of the mirrors changes the fringe spacing of the interference pattern generated. The array consists of four Fresnel mirrors each having an area of 2 × 2 mm2 arranged in a 2x2 configuration. The device, optimized using FEM simulations, is able to achieve maximum mirror deflections of 15 mrad, and has a resonance frequency of 28 kHz.