Characterisation of beam focus quality in biomedical nuclear microscopy: A Fourier optics approach

The central peak widths of the 2D-autocorrelation function have been investigated as a Figure of Merit (FoM) of focus quality in nuclear microscopy using a quadrupole triplet lens system. The beam focus could be reliably characterised for direct scanning transmission ion microscopy (direct-STIM) images obtained with fluences as small as 5.8×1095.8×109 ions cm-2cm-2 which colocalisation tests showed did not introduce significant beam-induced changes in the cells.