Antenna-coupled spintronic terahertz emitters driven by a 1550 nm femtosecond laser oscillator

Abstract

We demonstrate antenna-coupled spintronic terahertz (THz) emitters excited by 1550 nm, 90 fs laser pulses. Antennas are employed to optimize THz outcoupling and frequency coverage of ferromagnetic/nonmagnetic metallic spintronic structures. We directly compare the antenna-coupled devices to those without antennas. Using a 200 μm H-dipole antenna and an ErAs:InGaAs photoconductive receiver, we obtain a 2.42-fold larger THz peak-peak signal, a bandwidth of 4.5 THz, and an increase in the peak dynamic range (DNR) from 53 dB to 65 dB. A 25 μm slotline antenna offered 5 dB larger peak DNR and a bandwidth of 5 THz. For all measurements, we use a comparatively low laser power of 45 mW from a commercial fiber-coupled system that is frequently employed in table-top THz time-domain systems. This research was funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) through Project Nos. 290319996/TRR173, 318612841, and 278381540/PR1413/3-1 (REPHCON) and project B02 of the SFB/TRR227 Ultrafast Spin Dynamics. We further acknowledge CST for the EM Simulation solver.