Abstract

The feasibility of digital three-wavelength holographic interferometry is shown for analyzing the variations in the refractive index induced by the wake flow around a circular cylinder. The optical technique generates micro fringes in the observed field and the recording support is a specific CMOS sensor constituted with three stacked photodiode layers. The interference micro fringes produced by the superimposition of three reference waves and three measurement waves can be simultaneously recorded on the three spectral bands (red, green and blue). Phase and amplitude images are computed using Fourier transform in delayed time. Spectral filtering is applied on each Fourier plane in order to eliminate the parasitic diffraction orders and phase differences are obtained by subtracting the reference phase to the measurement phase. Fringes obtained with this process are those found by real-time color holographic interferometry using holographic plates. Interest by using color exhibiting the zero order white fringe can be easily shown as the variation in the background color due to the disturbances can be quantified between the two exposures.

© 2010 Optical Society of America