Mr. Sascha Keller Profile

Sascha Keller

at Rheinland-Pfälzische Technische Univ. Kaiserslautern-Landau

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Publications (2)

Proceedings Article | 1 March 2019 Paper

Efficient terahertz generation using Fe/Pt spintronic emitters pumped at different wavelengths

René Beigang, Evangelos Th. Papaioannou, Laura Scheuer, Sascha Keller, Garik Torosyan, Marco Rahm, Dominik Sokoluk, Miezel Talara, Yoshinori Oda, Hideaki Kitahara, Jessica Afalla, Valynn Katrine Mag-usara, Masahiko Tani

Proceedings Volume 10917, 109170O (2019) https://doi.org/10.1117/12.2514564

KEYWORDS: Terahertz radiation, Spintronics, Sensors

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Proceedings Article | 14 March 2018 Presentation

Spintronic terahertz emitters based on epitaxial-grown Fe/Pt Bilayers (Conference Presentation)

René Beigang, Garik Torosyan, Sascha Keller, Laura Scheuer, Evangelos Papaioannou

Proceedings Volume 10531, 1053105 (2018) https://doi.org/10.1117/12.2289489

KEYWORDS: Terahertz radiation, Spintronics, Sapphire, Magnetism, Silicon, Reflection, Antireflective coatings, Iron, Platinum, Gallium arsenide

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The inverse spin Hall effect (ISHE) can be used to generate broadband terahertz (THz) radiation. This has been demonstrated recently [1 – 3]. We report on efficient generation of pulsed broadband terahertz radiation utilizing the inverse spin hall effect in Fe/Pt bilayers on MgO and sapphire substrates. The magnetic and nonmagnetic layers were epitaxially grown on MgO and sapphire substrates. The emitter was optimized with respect to layer thickness, growth parameters, substrates and geometrical arrangement. Using the device in a counterintuitive orientation a hyperhemispherical Si lens was attached to increase the collection efficiency of the emitter. In this arrangement multiple reflections of the THz pulses from the substrate surfaces are avoided as the metallic layers act as an antireflection coating [4]. The experimentally determined dependence of the THz signal on the layer thicknesses was in qualitative agreement with simulations of the ISHE in the Fe-Pt bilayer. An optimum layer thicknesses of 2 nm and 3 nm were found for Fe and Pt, respectively. The optimized emitter provided a bandwidth of up to 8 THz for both the sapphire and MgO substrates which was mainly limited by the GaAs photoconductive antenna used as detector. The dynamic range reached 60 dB for the MgO substrate at a frequency of 1.5 THz. The pulse length was as short as 220 fs for a pump pulse length of the 800 nm pump laser of about 50 fs. In the case of MgO substrates strong THz absorption of MgO reduced the dynamic range above 3 THz considerably. Average pump powers as low as 25 mW (at a repetition rate of 80 MHz) have been used for terahertz generation. This and the general performance makes the spintronic terahertz emitter compatible with established emitters using nonlinear generation methods. References [1] T. Seifert et al., Nature Photonics 10, 483 (2016) [2] D. Yang, et al., Advanced Optical Materials. doi:10.1002/adom.201600270 (2016) [3] Y. Wu, Adv. Mater. doi:10.1002/adma.201603031 (2016) [4] J. Kröll et al., Optics Express 15, 6552 (2007)

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