Abstract-Modification of spintronic terahertz emitter performance through defect engineering

Dennis M. Nenno, Laura Scheuer, Dominik Sokoluk, Sascha Keller, Garik Torosyan, Alexander Brodyanski, Jörg Lösch, Marco Battiato, Marco Rahm, Rolf H. Binder, Hans C. Schneider, René Beigang,  Evangelos Th. Papaioannou

https://www.nature.com/articles/s41598-019-49963-8

Spintronic ferromagnetic/non-magnetic heterostructures are novel sources for the generation of THz radiation based on spin-to-charge conversion in the layers. The key technological and scientific challenge of THz spintronic emitters is to increase their intensity and frequency bandwidth. Our work reveals the factors to engineer spintronic Terahertz generation by introducing the scattering lifetime and the interface transmission for spin polarized, non-equilibrium electrons. We clarify the influence of the electron-defect scattering lifetime on the spectral shape and the interface transmission on the THz amplitude, and how this is linked to structural defects of bilayer emitters. The results of our study define a roadmap of the properties of emitted as well as detected THz-pulse shapes and spectra that is essential for future applications of metallic spintronic THz emitters.

Abstract-Electrically Reconfigurable Micromirror Array for Direct Spatial Light Modulation of Terahertz Waves over a Bandwidth Wider Than 1 THz

Jan Kappa, Dominik Sokoluk, Steffen Klingel, Corey Shemelya, Egbert Oesterschulze, Marco Rahm,

https://www.nature.com/articles/s41598-019-39152-y

We report the design, fabrication and experimental investigation of a spectrally wide-band terahertz spatial light modulator (THz-SLM) based on an array of 768 actuatable mirrors with each having a length of 220 μm and a width of 100 μm. A mirror length of several hundred micrometers is required to reduce diffraction from individual mirrors at terahertz frequencies and to increase the pixel-to-pixel modulation contrast of the THz-SLM. By means of spatially selective actuation, we used the mirror array as reconfigurable grating to spatially modulate terahertz waves in a frequency range from 0.97 THz to 2.28 THz. Over the entire frequency band, the modulation contrast was higher than 50% with a peak modulation contrast of 87% at 1.38 THz. For spatial light modulation, almost arbitrary spatial pixel sizes can be realized by grouping of mirrors that are collectively switched as a pixel. For fabrication of the actuatable mirrors, we exploited the intrinsic residual stress in chrome-copper-chrome multi-layers that forces the mirrors into an upstanding position at an inclination angle of 35°. By applying a bias voltage of 37 V, the mirrors were pulled down to the substrate. By hysteretic switching, we were able to spatially modulate terahertz radiation at arbitrary pixel modulation patterns.