Method for determining the aberration coefficients of the aberration function of a particle-optical lens

摘要

A lens of particle-optical apparatus, such as the objective lens, suffers from aberrations. As is already known since decades Ronchigrams can be used to determine these aberrations of particle-optical lenses.;Such methods rely e.g. on the determination of the 2^nd derivative of the aberration function on the basis of local magnification in one or a set of Ronchigrams. Being dependent on the 2^nd derivative the mathematics of these methods allow only (infinitesimal) small shifts between the Ronchigrams. However, this implies that e.g. the spatial quantization noise of the camera recording the Ronchigrams results in a large error. These conflicting requirements limit the accuracy and thus the usefulness of the known methods.;The invention describes a set of algorithms which result in an improved method to quantify the lens aberration coefficients using a set of Ronchigrams.