title: Fast and robust automatic calibration for single-shot dual-wavelength digital holography based on speckle displacements.
abstract: The objective of this paper is to describe a fast and robust automatic single-shot dual-wavelength holographic calibration method that can be used for online shape measurement applications. We present a model of the correction in two terms for each lobe, one to compensate the systematic errors caused by off-axis angles and the other for the curvature of the reference waves, respectively. Each hologram is calibrated independently without a need for an iterative procedure or information of the experimental set-up. The calibration parameters are extracted directly from speckle displacements between different reconstruction planes. The parameters can be defined as any fraction of a pixel to avoid the effect of quantization. Using the speckle displacements, problems associated with phase wrapping is avoided. The procedure is shown to give a shape accuracy of 34 μm using a synthetic wavelength of 1.1 mm for a measurement on a cylindrical test object with a trace over a field of view of 18  mm×18  mm.
authors.forename: Davood
authors.initials: D
authors.lastname: Khodadad
authors.forename: Per
authors.initials: P
authors.lastname: Bergström
authors.forename: Emil
authors.initials: E
authors.lastname: Hällstig
authors.forename: Mikael
authors.initials: M
authors.lastname: Sjödahl