Modified electronic speckle pattern interferometer with reduced number of elements for vibration analysis

An improved electronic speckle pattern interferometry (ESPI) system for vibration analysis by the time-average method is presented. The optical path length imbalance introduced in the interferometer allows us to implement a new phase shift heterodyning technique for vibration analysis by wavelength modulation of the light source. All the functions required for obtaining good visibility time average vibration fringes are implemented using laser diode modulation only. No additional phase modulator is required, the number of elements is reduced resulting in a greater flexibility of measurement procedures, equipment simplification and cost reduction are obtained, Illustrative results of studies of vibration objects are given.