Abstract: One embodiment relates to an apparatus for generating a charged particle beam with reduced energy width. A charged particle source is configured to generate a charged particle beam with a range of energies. An energy-dispersive device bends the high-energy component of the charged particle beam at less of an angle in comparison to the bending angle of the low-energy component of the charged particle beam, such that the higher and lower energy charged particle beam components exit the energy-dispersive device at different angles of trajectory. A charged particle mirror reflects the charged particle beam such that charged particles entering at an angle with respect to the normal to the mirror reflection plane exit the mirror symmetrically with respect to the normal and at the same angle. Charged particle lenses converge all energy components exiting the energy-dispersive device at different angles of trajectory at the charged particle mirror reflection plane.