Visualization 1 shows the focus changing with the applied voltage.

2017-12-06T19:05:28Z (GMT) by Lihui Wang
A video clip of our experiment is linked, which shows that the focal plane shifts from left to right of the target when the applied voltage is increased from zero to 5 kV and decteased to zero. In our experiment, the applied voltage was changed in steps of 0.5 kV.