As all solid-state terahertz emitters, spintronic terahertz emitters are subject to material destruction if a specific optical damage threshold is exceeded. This becomes a major challenge in applications where either a high electric field strength or a small beam diameter is required.

However, to date, only a few publications have addressed the challenge of optical damage threshold and these were limited to a low-repetition-rate regime below 400 kHz [1, 2]. To the best of the authors’ knowledge, the high-repetition-rate regime has not yet been targeted in a dedicated publication despite its critical importance for a variety of applications [3-5].

During the conference, we’d like to close this gap and introduce the necessity of classifying the optical damage threshold into two regimes: a low-repetition-rate regime characterized by a fluence-dependent threshold, and a high-repetition-rate regime characterized by an average-power-density dependent threshold (see Fig. 1 (c)). Taking advantage of our recently developed single-mode fiber-tip STEs [5], where the pump mode field is guaranteed to be nearly identical for each sample due to their waveguiding nature, we were able to measure the optical damage thresholds with high accuracy. By repeating the experiment at various repetition rates between 100 kHz and 1 GHz (and CW), we were able to prove the existence of the yet unpublished high-repetition-rate optical damage regime and to identify the transition point between the low- and high-repetition-rate regime.