Spintronic terahertz emitters (STEs) are powerful sources of ultra-broadband single-cycle terahertz (THz) field transients. They work with any pump wavelength, and their polarity and polarization direction are easily adjustable. However, at high pump powers and high repetition rates, STE operation is hampered by a significant increase in the local temperature. Here, we resolve this issue by rotating the STE at a few 100 Hz, thereby distributing the absorbed pump power over a larger area. Our approach permits stable STE operation at a fluence of ∼1 mJ/cm2 with up to 18 W pump power at megahertz repetition rates, corresponding to pump-pulse energies of a few 10 μJ and pump power densities approaching 1 kW/cm2. The rotating STE is of interest for all ultra-broadband high-power terahertz applications requiring high repetition rates. As an example, we show that terahertz pulses with peak fields of 10 kV/cm can be coupled to a terahertz-light wave-driven scanning tunneling microscope at 1 MHz repetition rate, demonstrating that the rotating STE can compete with standard terahertz sources such as LiNbO3.
