Rotating spintronic terahertz emitter optimized for microjoule pump-pulse energies and megahertz repetition rates

TL;DR

This paper presents a rotating spintronic terahertz emitter that maintains stable, high-power operation at megahertz repetition rates by distributing heat, enabling advanced high-repetition-rate THz applications.

Contribution

The study introduces a rotating mechanism for spintronic THz emitters that allows stable operation at high pump powers and repetition rates, overcoming thermal limitations of static devices.

Findings

Stable operation at ~1 mJ/cm² fluence and 18 W pump power.

Achieved THz pulses with 10 kV/cm peak fields at 1 MHz.

Comparable performance to standard THz sources like LiNbO₃.

Abstract

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/cm$^2$ with up to 18 W pump power at megahertz repetition rates, corresponding to pump-pulse energies of a few 10 $\mu$J and a power density far above the melting threshold of metallic films. The rotating STE is of interest for all ultra-broadband high-power THz applications requiring high repetition rates. As an example, we show that THz pulses with peak fields of 10 kV/cm can be coupled to a THz-lightwave-driven scanning tunneling microscope at 1 MHz repetition rate, demonstrating that the rotating STE can compete with standard THz sources such as LiNbO$_3$.