One embodiment relates to an apparatus for generating two spatially overlapping electron beams on a specimen. A first electron beam source is configured to generate a low-energy electron beam, and an energy-dispersive device bends the low-energy electron beam towards an semitransparent electron mirror. The semitransparent electron mirror is biased to reflect the low-energy electron beam. A second electron beam source is configured to generate a high-energy electron beam that passes through an opening in the semitransparent electron mirror. Both the low- and high-energy electron beams enter the same energy-dispersive device that bends both beams towards the specimen. A deflection system positioned between the high-energy electron source and semitransparent electron mirror is configured to deflect the high-energy electron beam by an angle that compensates for the difference in bending angles between the low- and high-energy electron beams introduced by the energy-dispersive device. Other embodiments are also disclosed.