Laser-free GHz stroboscopic TEM: components, system integration, and practical considerations for pump-probe measurements
June W. Lau, Karl B. Schliep, Michael B. Katz, Vikrant J. Gokhale, Jason J. Gorman
A 300 keV transmission electron microscope was modified to produce broadband pulsed beams, that can be in principle, between 40 MHz to 12 GHz, corresponding to temporal resolution in the nanosecond to picosecond range without an excitation laser. The key enabling technology is a pair of phase-matched modulating and de-modulating Traveling Wave Metallic Comb Striplines (pulsers). An initial temporal resolution of 30 ps was achieved with a strobe frequency of 6.0 GHz. The placement of the pulsers, mounted immediately below the gun, allows for the preservation of all optical configurations otherwise available to the unmodified instrument, and therefore makes such a post-modified instruments dual-use, i.e., both pulsed-beam mode (i.e., stroboscopic time-resolved) and conventional continuous waveform (CW) mode. In this article, we describe the elements inserted into the beam path, challenges encountered during integration with an in-service microscope, and early results from an electric-field-driven pump-probe experiment. We conclude with ideas for making this class of instrument broadly applicable for examining cyclical and repeatable phenomena.