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Imaging electromagnetic waveforms
Understanding the dynamics of electrons and the spatial and temporal evolution of electromagnetic fields within a material or device is often the key to optimizing performance. Ryabov and Baum show that electron microscopy can be used to measure collective carrier motion and electromagnetic fields with subcycle and subwavelength resolution. As an example, they used a train of compressed electron pulses to produce movies of the electromagnetic excitation in an optical excited metamaterial component.
Science, this issue p. 374
Abstract
Rapidly changing electromagnetic fields are the basis of almost any photonic or electronic device operation. We report how electron microscopy can measure collective carrier motion and fields with subcycle and subwavelength resolution. A collimated beam of femtosecond electron pulses passes through a metamaterial resonator that is previously excited with a single-cycle electromagnetic pulse. If the probing electrons are shorter in duration than half a field cycle, then time-frozen Lorentz forces distort the images quasi-classically and with subcycle time resolution. A pump-probe sequence reveals in a movie the sample’s oscillating electromagnetic field vectors with time, phase, amplitude, and polarization information. This waveform electron microscopy can be used to visualize electrodynamic phenomena in devices as small and fast as available.
