Harmonic calibration of quadrature phase interferometry

TL;DR

This paper introduces two novel calibration methods for quadrature phase interferometers that significantly improve linearity and measurement accuracy, demonstrated through optical interferometry of force microscopy cantilevers.

Contribution

The authors propose alternative calibration techniques based on sinusoidal response, offering a tenfold improvement over traditional ellipse fitting methods.

Findings

Achieved tenfold linearity improvement in calibration.

Demonstrated effectiveness on optical interferometers.

Enhanced measurement accuracy for force microscopy.

Abstract

The two output signals of quadrature phase interferometers allow to benefit both from the high sensitivity of interferometry (working inside a fringe) and from an extended input range (counting fringes). Their calibration to reach a linear output is traditionally performed using Heydemann's correction, which involves fitting one output versus the other by an ellipse. Here we present two alternative methods based on the linear response of the measurement to a sinusoidal input in time, which enables a direct calibration with an excellent linearity. A ten fold improvement with respect to the usual technique is demonstrated on an optical interferometer measuring the deflection of scanning force microscopy cantilevers.