Compact FPGA based Multi-Axial Interferometer Applied in a Metrological Atomic Force Microscope

摘要

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 Angstrom 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.