title: High bandwidth deflection readout for atomic force microscopes.
abstract: This contribution presents the systematic design of a high bandwidth deflection readout mechanism for atomic force microscopes. The widely used optical beam deflection method is revised by adding a focusing lens between the cantilever and the quadrant photodetector (QPD). This allows the utilization of QPDs with a small active area resulting in an increased detection bandwidth due to the reduced junction capacitance. Furthermore the additional lens can compensate a cross talk between a compensating z-movement of the cantilever and the deflection readout. Scaling effects are analyzed to get the optimal spot size for the given geometry of the QPD. The laser power is tuned to maximize the signal to noise ratio without limiting the bandwidth by local saturation effects. The systematic approach results in a measured -3 dB detection bandwidth of 64.5 MHz at a deflection noise density of 62fm/√Hz.
authors.affiliation: Automation and Control Institute (ACIN), Vienna University of Technology, Gusshausstrasse 27-29/E376, 1040 Wien, Austria.
authors.forename: Juergen
authors.initials: J
authors.lastname: Steininger
authors.affiliation: Automation and Control Institute (ACIN), Vienna University of Technology, Gusshausstrasse 27-29/E376, 1040 Wien, Austria.
authors.forename: Matthias
authors.initials: M
authors.lastname: Bibl
authors.affiliation: Automation and Control Institute (ACIN), Vienna University of Technology, Gusshausstrasse 27-29/E376, 1040 Wien, Austria.
authors.forename: Han Woong
authors.initials: HW
authors.lastname: Yoo
authors.affiliation: Automation and Control Institute (ACIN), Vienna University of Technology, Gusshausstrasse 27-29/E376, 1040 Wien, Austria.
authors.forename: Georg
authors.initials: G
authors.lastname: Schitter