We have recently shown that the emission spectrum of spintronic THz emitters (STE) is largely influenced by charge dynamics that result from charging and discharging effects. This effect is present in any large area STE. In recent experiments, we have demonstrated that the current backflow can be controlled by using arrays of patterned STE with each of the emitters being smaller than the laser spot. We show that by using differently sized respective emitters we can modify especially the lower part of the spectrum and are able to suppress the emission of spectral components lower than 4 THz while elongated emitters allow us to extend the spectrum even to lower frequencies. The experimental results can be reproduced by an analytical model based on the emission of a large area emitter. Without any fitting parameters, we can model the emission of STE of various sizes with surprising accuracy. On the other hand, arrays of linear emitters can be used to emit a sequence of pulses as a kind of grating in time. These allow us to emit narrow band THz radiation as a THz burst with an arbitrary fundamental frequency, in our case up to 20 THz.

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Georg Schmidt, "Shaping the emission spectrum of spintronic THz emitters by nanopatterning," Proc. SPIE PC13119, Spintronics XVII, PC131190W (Presented at Nanoscience + Engineering: August 20, 2024; Published: 4 October 2024); https://doi.org/10.1117/12.3027069.137d8497-7abf-ee11-a99d-c49c781f4d15.