Patent ID: 7800076

Claim:
A particle-optical corrector for eliminating both a third-order aperture aberration and a third-order extra-axial coma using circular lenses and hexapole fields, comprising: a corrector having three coaxially-arranged hexapole fields with intensities of said hexapole fields being selected so that an image aberration coefficient of an astigmatism with three-fold symmetry becomes zero and that said corrector contains two hexapole field pairs, wherein hexapole fields of each hexapole field pair of said two hexapole field pairs are excited anti-symmetrically relative to one another; and, at least one circular lens doublet arranged between adjacent said hexapole fields and adjustable so that a center hexapole field of said hexapole fields is imaged on said hexapole fields for causing two intermediate planes to lie between said hexapole fields, said two intermediate planes being conjugated with one another and said three coaxially-arranged hexapole fields being identically oriented in a Larmor reference system, each said hexapole field pair being each being arranged around said two intermediate planes and an orientation of said hexapole field pairs being rotated relative to an orientation of said hexapole fields by an angle so that an extra-axial third order coma is corrected.