Ultrafast Electron Diffraction
Schematic view of ultrafast electron diffraction experiments. Diffraction with an electron bunch follows photoexcitation. Varying the time-delay Δt allows for a complete time-resolved view of the structural dynamics.
The methods we are developing combine electron microscopes with femtosecond pulsed lasers in novel ways. Using the method of UED we are able to image novel phases of matter with electronic, structural, or magnetic order that are inaccessible by conventional routes.
High bunch charge emission of electrons using THz driven metal nanotips
Critical to UED is source of electron pulses. To this end, the Cooke group has developed a method capable of producing large bunch charges in excess of 10^6 electrons. To achieve this, we shine THz pulses with peak fields that approach MV/cm on the apex of a metal nanotip. At these fields, electrons are pulled directly from the metal and are accelerated to keV energies in < 10 fs.
Manufacturing Tungsten Nanotips
SEM image of a tungsten nanotip without exposure (120 nm radius)(left) and with exposure to > 1 billion of THz shot (35 nm radius)(right) showing a strong reshaping/sharpening of the apex of the tungsten nanotip improving the electrons emission rate and energy.