Patent ID: 8299442

Claim:
A particle beam apparatus defining an optical axis and comprising: an illuminating system for illuminating an object to be positioned in an object plane with a beam of charged particles which splits into a null beam and higher diffraction orders at said object; an objective arranged along said optical axis for imaging said object illuminated by said illuminating system; said illuminating system being configured to generate, during operation, an annularly-shaped illuminating aperture in a plane fourier transformed to said object plane; said objective having a focal plane facing away from said object plane; a phase-shifting element mounted in said focal plane or a plane conjugated thereto; said phase-shifting element including an einzel lens having first and second outer electrodes arranged along said optical axis and an inner electrode arranged therebetween; said electrodes being arranged and charged with electrical potential, during operation, so as to cause the potential at said optical axis to correspond to the potential at said first and second outer electrodes of said einzel lens; and, wherein said phase-shifting element further comprises an ancillary electrode on or near said optical axis.