Dynamic focusing of microprobe lens system during scanning process

Highly excited quadrupole lenses have significant spherical aberrations and they are very sensitive to the beam entrance angle, and microprobe size may vary considerably during scanning if the scanner is placed before or inside the focusing system. The effect of probe blurring while moving away from the optical axis can be partially compensated by adopting a dynamic focusing procedure to systems of magnetic quadrupole lenses like it is in electron beam devices. Dynamic focusing implies changing of quadrupole lens currents synchronously with the beam deflection on the certain rule such that probe size remains minimal in any raster point. A quadruplet of magnetic quadrupole lenses was considered.