Nonlinear systems can be probed by driving them with two or more pure tones while measuring the intermodulation products of the drive tones in the response. We describe a digital lock-in analyzer which is designed explicitly for this purpose. The analyzer is implemented on a field-programmable gate array, providing speed in analysis, real-time feedback and stability in operation. The use of the analyzer is demonstrated for Intermodulation Atomic Force Microscopy. A generalization of the intermodulation spectral technique to arbitrary drive waveforms is discussed.
@article{arxiv.1008.2722,
title = {The Intermodulation Lockin Analyzer},
author = {Erik A. Tholen and Daniel Platz and Daniel Forchheimer and Vivien Schuler and Mats O. Tholen and Carsten Hutter and David B. Haviland},
journal= {arXiv preprint arXiv:1008.2722},
year = {2013}
}