Quasi-common path three-wavelength holographic interferometer based on Wollaston prisms

•Digital color holography is demonstrated in fluid.•Color allows quantifying the initial optical path difference due to external vibrations.•Opportunity for a real time three dimensional sensing in given.•Use of Wollaston prisms for generating three spatial carrier frequencies.•The applications to real-time 3D measurement shows quite satisfactory results.

This article presents a digital three-wavelength holographic interferometer based on the use of two Wollaston prisms. This provides an in-line setup with quasi common-path and as a consequence there is no additional independent reference wave to be added. Thus, immunity to external perturbations such as vibrations or thermal perturbations is achieved. Furthermore, the set-up exhibits a single shot and real time capability which is very useful to study dynamic events. By using the two Wollaston prisms in an astigmatic configuration, spatial carrier frequencies can be adjusted both in amplitude and orientation. The digital hologram processing is based on Fourier processing and filtering around the carrier spatial frequency so that phase shifting is not required. The use of three wavelengths leads to visualizing directly the zero order fringe and regions for which there is no air density variation in a dynamic flow. Experimental proof of concept is demonstrated with a supersonic jet when the injection pressure varies.