Single stage charged particle beam energy width reduction system for charged particle beam system

Method of reducing a charged particle beam velocity distribution width with a system comprising a z-axis along an optical axis, an element acting in a focusing and dispersive manner having essentially a z-position Zc, a quadrupole element, a first charged particle selection element and a second charged particle selection element, comprising:

• generating a crossover at the position zc with a first lens;
• selecting charged particles with the first charged particle selection element;
• exciting the element acting in a focusing and dispersive manner and the quadrupole element;
• adjusting the field strength of the element acting in a focusing and dispersive manner and the quadrupole element so that there is no focusing effect in a x-z-plane and that the charged particle beam appears to originate from the x-y-center-plane of the element acting in a focusing and dispersive manner with respect to a y-z-plane;
• and
• velocity dependently selecting charged particles with the second charged particle selection element.