Fig. 2.

Comparative performances of an objective piezo-stage and of the electrical lens. a) Schematics of the orbital tracking configuration. A full 3D tracking period is achieved by performing 4 radial periods: 2 above and 2 below the particle. b) Piezo and lens performance compared for an orbit period of 8.192 ms. The up-down period for orbital tracking 32.77 ms. Comparing the displacement of the focal plane achieved by movement of the objective (Piezo, blue line, 2) and by the use of the ETL (Lens, red line, 1) c) Comparing piezo and lens performance for an orbital period of 2.048 ms. d) Demodulation of the piezo response for decreasing orbit period. The ideal square wave response turns to a triangular wave response, as the device is not able to perform the entire axial excursion in the required time e) Lens focal offset of ETL response for increasing axial frequency (i.e. decreasing orbit period, as indicated in the top axis). A resonance at about 500Hz is observed.