Digital holographic interferometry has been developed by ONERA for analysing high refractive index variations encountered in fluid mechanics. First, the authors present the analysis of a small supersonic jet using three different optical techniques based on digital Michelson holography, digital holography using Wollaston prisms and digital holography without reference wave. A comparison of the three methods is given. Then, two different interferometers are described for analysing high‐density gradients encountered in high subsonic and transonic flows. The time evolution of the gas density field around a circular cylinder is given at Mach 0.7. Finally, a digital holographic method is presented to visualize and measure the refractive index variations occurring inside a transparent and strongly refracting object. For this case, a comparison with digital and image holographic interferometry using transmission and reflection holograms is provided.
Part of the book: Holographic Materials and Optical Systems