Hoffrogge et al. recently posted a pre-print to the arXiv describing a laser-heated field emission source demonstrating sub-100 femtosecond pulsed electron emission. There have been previous disclosures of laser-heated field emission cathodes (see, for example US 6,828,996 and references therein), but none have been designed for pulsed emission.
The new source should find application in time-resolved electron diffraction. The coherence of the source has apparently not yet been established. The implementation shown operates at 30 keV.
Another application comes to mind – pump-probe spectroscopy. In the usual scheme, a femto-second laser pulse is used to excite a target molecule, while a second, time-delayed pulse measures the decay product. One can envision replacing the pump laser pulse with a pump electron beam pulse. Since the selection rules for energy absorption are entirely different for photons and electrons, the excited states and resultant decay channels will also differ. Comparing photo-pumped and electron-pumped systems could, for example, clarify why EUV resists are generally not particularly good electron-beam resists and vice versa.
A recent advance in laser pump-probe spectroscopy, involving a third photon pulse, would be very useful here as well, since we know that electron impact with resist yields a vast number of excited states.