Manipulation of terahertz spectrum using microfabricated magnetic heterostructures*

Terahertz (THz) radiation with sub-micrometer wavelength falls in the gap between the optical and radio frequency range. Conventional THz emitters rely only on the electron's charge. However, recently it was found that spin-based effects occur on the ultrafast time scale. Upon excitation with a femtosecond laser pulse a diffusive spin current is created in a ferromagnet that leads to THz transients in an adjacent heavy metal layer due to a conversion by the inverse spin Hall effect. Here, we demonstrate generation and control of THz radiation from microstructured Fe/Pt bilayers. We compare the THz spectrum of different patterns and an extended film using time-domain THz spectroscopy. The microstructures are fabricated using optical lithography and sputtering deposition. The THz spectrum is experimentally observed and interpreted in terms of a simplified multi-slit diffraction model, which captures the main experimental features. Our results show an efficient control of the emitted THz light. This is a crucial step forward for the design and realization of directional spin-based THz sources.