Measurement of all orthogonal components of displacement in the volume of scattering materials using wavelength scanning interferometry.

A wavelength scanning interferometry system is proposed that provides displacement fields inside the volume of semitransparent scattering materials with high spatial resolution and three-dimensional (3D) displacement sensitivity. This effectively extends digital speckle pattern interferometry into three dimensions. The sample is illuminated by three noncoplanar collimated beams around the observation direction. Sequences of two-dimensional interferograms are recorded while tuning the laser frequency at a constant rate. Different optical paths along each illumination direction ensure that the signals corresponding to each sensitivity vector do not overlap in the frequency domain. All the information required to reconstruct the location and the 3D displacement vector of scattering points within the material is thus recorded simultaneously. A controlled validation experiment is performed, which confirms the ability of the technique to provide 3D displacement distributions inside semitransparent scattering materials.