Electron energy analysis by phase-space shaping with THz field cycles

Time-resolved electron energy analysis and loss spectroscopy can reveal a wealth of information about material properties and dynamical light-matter interactions. Here, we report an all-optical concept for measuring energy spectra of femtosecond electron pulses with sub-eV resolution. Laser-generated terahertz radiation is used to measure arrival time differences within electron pulses with few-femtosecond precision. Controlled dispersion and subsequent compression of the electron pulses provide almost any desired compromise of energy resolution, signal strength, and time resolution. A proof-of-concept experiment on aluminum reveals an energy resolution of <3.5 eV (rms) at 70-keV after a drift distance of only 0.5 m. Simulations of a two-stage scheme reveal that pre-stretched pulses can be used to achieve <10 meV resolution, independent of the source's initial energy spread and limited only by the achievable THz field strength and measuring time

A spatially and temporally localized sub-laser-cycle electron source

We present an experimental and numerical study of electron emission from a sharp tungsten tip triggered by sub-8 femtosecond low power laser pulses. This process is non-linear in the laser electric field, and the non-linearity can be tuned via the DC voltage applied to the tip. Numerical simulations of this system show that electron emission takes place within less than one optical period of the exciting laser pulse, so that an 8 fsec 800 nm laser pulse is capable of producing a single electron pulse of less than 1 fsec duration. Furthermore, we find that the carrier-envelope phase dependence of the emission process is smaller than 0.1% for an 8 fsec pulse but is steeply increasing with decreasing laser pulse duration.Comment: 4 pages, 5 figure