  We demonstrate a 2-grating free electron Mach-Zehnder interferometer
constructed in a transmission electron microscope. A symmetric binary phase
grating and condenser lens system forms two spatially separated, focused probes
at the sample which can be scanned while maintaining alignment. The two paths
interfere at a second grating, creating in constructive or destructive
interference in output beams. This interferometer has many notable features:
positionable probe beams, large path separations relative to beam width,
continuously tunable relative phase between paths, and real-time phase
information. Here we use the electron interferometer to measure the relative
phase shifts imparted to the electron probes by electrostatic potentials as
well as a demonstration of quantitative nanoscale phase imaging of a
polystyrene latex nanoparticle.
