Cavity-Dumping a Single Infrared Pulse from a Free-Electron Laser for Two-Color Pump-Probe Experiments

TL;DR

This paper presents a cavity-dumping technique for free-electron lasers to generate single, high-energy, picosecond infrared pulses, enabling advanced two-color pump-probe experiments for studying magnetization dynamics.

Contribution

The study introduces a novel cavity-dumping setup for free-electron lasers that produces tunable, high-energy infrared pulses suitable for single-shot pump-probe measurements.

Findings

Generated >100 μJ infrared pulses with variable duration.

Enabled single-shot imaging of magnetization dynamics.

Demonstrated resonant phononic switching detection.

Abstract

Electromagnetic radiation in the mid- to far-infrared spectral range represents an indispensable tool for the study of numerous types of collective excitations in solids and molecules. Short and intense pulses in this THz spectral range are, however, difficult to obtain. While wide wavelength-tunability is easily provided by free-electron lasers, the energies of individual pulses are relatively moderate, on the order of microjoules. Here we demonstrate a setup that uses cavity-dumping of a free-electron laser to provide single, picosecond-long pulses in the mid- to far-infrared frequency range. The duration of the Fourier-limited pulses can be varied by cavity detuning, and their energy was shown to exceed 100 {\mu}J. Using the aforementioned infrared pulse as a pump, we have realized a two-color pump-probe setup facilitating single-shot time-resolved imaging of magnetization dynamics. We demonstrate the capabilities of the setup first on thermally-induced demagnetization and magnetic switching of a GdFeCo thin film and second by showing a single-shot time-resolved detection of resonant phononic switching of the magnetization in a magnetic garnet.