## Tuesday, April 20, 2021

### Abstract-Switchable generation of azimuthally- and radially-polarized terahertz beams from a spintronic terahertz emitter

Hiroaki Niwa, Naotaka Yoshikawa, Masashi Kawaguchi, Masamitsu Hayashi, and Ryo Shimano

 (a) THz generation from a spintronic THz emitter. Transient spin current 𝐣s${\mathbf{j}}_{\mathrm{s}}$ generated upon photoexcitation converts into charge current 𝐣c${\mathbf{j}}_{\mathrm{c}}$ via the inverse spin Hall effect, which radiates THz electric field with the polarization perpendicular to the magnetization 𝐦̂ $\stackrel{^}{\mathbf{m}}$. (b) Schematic of the experimental setup. (c) and (d) Schematic presentation of generating azimuthal and radial polarization by converting HE21${\text{HE}}_{\text{21}}$ mode with different orientations, respectively.
https://www.osapublishing.org/oe/fulltext.cfm?uri=oe-29-9-13331&id=450178

We propose and demonstrate a method of generating two fundamental terahertz cylindrical vector beams (THz-CVBs), namely the azimuthally- and radially-polarized THz pulses, from a spintronic THz emitter. We begin by presenting that the spintronic emitter generates the HE21 mode, a quadrupole like polarization distribution, when placed between two magnets with opposing polarity. By providing an appropriate mode conversion using a triangular Si prism, we show both from experiment and numerical calculation that we obtain azimuthal and radial THz vector beams. The proposed method facilitates the access of CVBs and paves the way toward sophisticated polarization control in the THz regime.

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