  Novel schemes for generating ultra-low emittance electron beams have been
developed in the last years and promise compact particle sources with excellent
beam quality suitable for future high-energy physics experiments and
free-electron lasers. Current methods for the characterization of low emittance
electron beams such as pepperpot measurements or beam focus scanning are
limited in their capability to resolve emittances in the sub $0.1$ mm mrad
regime. Here we propose a novel, highly sensitive method for the single shot
characterization of the beam waist and emittance using interfering laser beams.
In this scheme, two laser pulses are focused under an angle creating a
grating-like interference pattern. When the electron beam interacts with the
structured laser field, the phase space of the electron beam becomes modulated
by the laser ponderomotive force and results in a modulated beam profile after
further electron beam phase advance, which allows for the characterization of
ultra-low emittance beams. 2D PIC simulations show the effectiveness of the
technique for normalized emittances in the range of $\epsilon_n=[0.01,1]$ mm
mrad.
