Electronic speckle-pattern interferometer using holographic optical elements for vibration measurements

We report a simple, compact electronic speckle-pattern interferometer (ESPI) incorporating holographic optical elements (HOEs) for the study of out-of-plane vibration. Reflection and transmission HOEs provide reference and object beams in the interferometer. The alignment difficulties with conventional ESPI systems are minimized using HOEs. The time-average ESPI subtraction method is used to generate the fringe pattern and remove background speckle noise by introducing a phase shift between consecutive images. The amplitude and phase maps are obtained using path-difference modulation.