A digital phase-measurement system for real-time holographic interferometry

While holographic interferometry gives a good picture of the stress distribution over a complex structure, its use in stress-analysis has been limited by the fact that quantitative information on the deformation of the surface is directly available only at points on the fringe maxima or minima, and interpolation between these points is slow and not very accurate. An improved phase-measurement system for real-time holographic interferometry is described. This uses a diode array television camera to view the interference pattern, and digital electronics to calculate and store the phase difference at a 100 × 100 grid of points. This permits measurements of the phase with an accuracy estimated at ±2°.