Three-bucket quadrature phase stepping in a shearing speckle interferometer

Abstract

Phase stepping algorithms are mostly based on three or more interferograms that can either be acquired sequentially, involving some temporal phase stepping mechanism, or in parallel. When a phase step is applied between acquisitions, object phase changes may cause phase errors when calculating phase. A new system that allows the object to change in between arbitrary temporal phase steps is proposed. It comprises a relatively simple polarization based two-channel speckle interferometer that acquires two π/2 phase stepped interferograms simultaneously with a single camera. This quadrature pair is phase stepped with a temporal phase stepping system that is also polarization based. Simulations and experimental results are presented that illustrate the improvements achieved with quadrature phase stepping compared to results obtained with the two-channel speckle interferometer operated without additional temporal phase stepping.

A new Method for Processing Time Averaged Vibration Patterns: Linear Regression

“…This is true in most cases, but not all, for instance, not when quadrature phase‐stepping is applied. In that case phase difference can also be calculated without knowing the temporal phase steps .…”

“…The object was excited by a loudspeaker on the backside, at a frequency of 147 Hz. The speckle interferometer used was a modified subsystem of an existing shearography system . The subsystem, a polarisation‐sensitive shearing interferometer in Michelson configuration, is shown in Figure .…”