Ultrafast Electron Temperature Dynamics in Spintronic Terahertz Emitters Studied by Optical-Pump Terahertz-Probe Spectroscopy

Abstract: Spintronic terahertz emitters pumped by femtosecond lasers offer an increasingly popular approach to generate broadband terahertz radiation. The strength of the emitted terahertz field is limited in part by the optical damage threshold at the pump wavelength of the spintronic terahertz emitter. Their thermal management can be improved by better understanding the electron temperature relaxation in the spintronic metal layer. Here we present a measurement of the electron temperature dynamics on a picosecond timescale using optical-pump terahertz-probe spectroscopy. We observe that the optical pump induces a change in the terahertz transmission of the spintronic terahertz emitter. By measuring the resulting terahertz signal and employing a two-temperature model, we are able to calculate the dynamic electron temperature of the STE. This approach offers an advantage over other methods by avoiding additional heating of the sample by the probe pulse. This is especially significant for measurements of accumulative heat effects, which can dominate the optical damage mechanism when the spintronic terahertz emitter is pumped at a MHz repetition rate.