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Updated: May 7, 2026

Sub-nanometer Resolution Imaging with Amplitude-modulation Atomic Force Microscopy in Liquid
Published on: December 20, 2016
Heterodyne interferometer for absolute amplitude vibration measurements with femtometer sensitivity
Abstract:
A heterodyne interferometer for highly sensitive vibration measurements in the range 100 kHz - 1.3GHz is presented. The interferometer measures absolute amplitude and phase. The signal processing of the setup is analyzed and described in detail to optimize noise suppression. A noise floor of 7.1 fm/Hz(1/2) at 21 MHz was achieved experimentally where the bandwidth is the inverse of all time needed for filter settling and signal sampling. To demonstrate the interferometer, measurements up to 220 MHz were performed on arrays of capacitive micromachined ultrasonic transducers (CMUTs). The measurements provided detailed information e.g. about the frequency response, vibration patterns and array uniformity. Such measurements are highly valuable in the design process of ultrasonic transducers.
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