Electron microscopy experiments concerning hysteresis in the magnetic lens system

Ferromagnetic hysteresis and coupled dynamics in the magnetic lens system of electron microscopes degrade the machine's performance in terms of steady-state error and transition time. To get a clear understanding of the exact problem and the way it is expressed in the application a commercial scanning electron microscope is extended with a data-acquisition and rapid proto-typing system. By means of conditioned experiments the significance of the hysteresis effects for microscopy applications is quantified. The response is evaluated by an analysis of synchronized lens currents and estimated sharpness of the resulting images. The sensitivity of image sharpness versus input variation is obtained in a local operating point. The hysteresis effect and its coupling with dynamics, as a response to changes over the complete working range, result in a significant deviation in image sharpness. Since the magnetic field is not available for measurement, the error is expressed in the quasi-static input variation required to correct for it. In order to get a good understanding of the observed effects and the magnetic lens as a system, an interconnected dynamics-hysteresis-electron optics model is used to analyze and to reproduce the experimental results.