COMPACT FPGA BASED MULTI-AXIAL INTERFEROMETER APPLIED IN A METROLOGICAL ATOMIC FORCE MICROSCOPE

Sebastian Strube, Gabor Molnar, Hans-Ulrich Danzebrink

Abstract

For use in a new, metrological atomic force microscope (AFM) a highly compact interferometer, based on a modified homodyne Twyman-Green interferometer concept was developed at PTB. It is modular, measures displacement and tilt simultaneously, allows for traceability and an uncertainty in the Ångstrom range. A novel signal processing approach based on a field programmable gate array (FPGA) is employed, whereby a spatial interferogram is acquired by a high-speed line sensor and transformed into its frequency spectrum through a discrete Fourier transform. The AFM combines an FPGA for preprocessing, a digital signal processor (DSP) which runs the AFM control algorithm and a general purpose processor (GPP) for user-interface handling and mass data storage. The complete system allows for implementing a multitude of different AFM measuring modes, e.g. contact mode, intermittent contact mode using amplitude detection and phase detection or frequency tracking mode.

Keywords

interferometry, FPGA, nanometrology, nanoscale, atomic force microscopy (AFM), nanopositioning, tilt measurement, distance measurement

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IMEKO-TC14-2011-46.pdf

DOI

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IMEKO TC

TC14 - Measurement of Geometrical Quantities

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