Charged particle analyser and method

A charged particle analyser comprising:

• a first non-imaging electrostatic lens for receiving charged particles having divergent trajectories and for converting the said trajectories into substantially parallel trajectories;
• at least one planar filter, comprising one or more electrostatic filter grids, for receiving the charged particles having the said substantially parallel trajectories and for filtering the charged particles in accordance with their respective energies, wherein the filter is adapted to provide a decelerating field to prevent passage of charged particles having energies below a predetermined threshold;
• a second non-imaging electrostatic lens for receiving the energy filtered charged particles and selectively modifying their trajectories as a function of their energies;
• and
• a charged particle detector for receiving the charged particles in accordance with their selectively modified trajectories.