Pump-probe cathodoluminescence microscopy

In this paper we describe the technical implementation of pump-probe cathodoluminescence microscopy (PP-CL), a novel technique for studying ultrafast dynamics in materials using combined excitation of electron and laser pulses. The PP-CL setup is based on a commercial scanning electron microscope combined with a femtosecond laser. Here we discuss the design, technical details, and characterization of the PP-CL setup. The luminescence emitted by the sample (either photoluminescence, cathodoluminescence or a combination of both) can be analyzed in terms of spectrum, temporal statistics, and frequency-modulated intensity (lock-in detection). The laser spot on the sample is characterized by analyzing the changes in the secondary electron signal on a GaN substrate, from which we extract a laser spot size in the $\mu m$ range. While this method ensures spatial overlap of laser and electron pulses on the sample, temporal alignment is achieved using time-correlated measurements of photoluminescence and cathodoluminescence. We also discuss some considerations to take into account when designing a PP-CL experiment, regarding temporal and spatial resolution. This paper provides a detailed reference for the development of any PP-CL microscope.