RUIZ, P.D., 2013. Tomographic sensing of displacement fields. Presented at: Optical Sensors, 14th-17th July 2013, Rio Grande, Puerto Rico.
A wavelength scanning interferometry system is used to measure all the orthogonal
components of the displacement field inside semitransparent scattering materials. A near infrared
tunable laser illuminates a sample from multiple directions. The image of the sample is
recombined with a reference beam on a photodetector array. As the laser frequency is linearly
tuned during a scan, a sequence of speckle interferograms is recorded. In order to reconstruct the
sample structure, Fourier transformation is performed on a pixel by pixel basis along the temporal
axis of the 3-D data cube obtained. Multiple displacement sensitivities are achieved by introducing
different optical delays between the reference and the illumination beams, which separate the
reconstruction signals in the frequency domain. Phase changes due to mechanical loading of the
sample can finally be measured and combined to obtain all orthogonal components of the
displacement field in a convenient coordinate system. Controlled rigid body rotations of an epoxy
phantom have been used to validate the methodology.