Photoelectron scanning electron microscope (PSEM) for high speed noncontact testing

The electron emitter in a conventional SEM is replaced by a pulsed laser/photocathode combination, resulting in a source producing electron pulses of order 1 ps in duration at a 100 Mhz repetition rate and with a peak brightness of 3 108 A/cm2.steradian. By using this instrument in the voltage contrast mode, without contact with the samples, we have been able to measure electrical pulses propagating on coplanar transmission lines with a temporal resolution of 5 ps, a voltage resolution of 3 mV/(Hz)1/2 and a spatial resolution of 0.1 μm. These measurements are achieved with extraction fields above the sample of about 1 kV/mm.