Combined fibre optic laser velocimeter and electronic speckle pattern interferometer with a common reference beam

A novel optical fibre system, for out-of-plane vibration analysis, comprising the complementary techniques of laser velocimetry and electronic speckle pattern interferometry, is described. The laser velocimeter (LV) and the electronic speckle pattern interferometer (ESPI) share a common reference arm and phase modulator. The LV locks to the motion of a point on the vibrating surface and since the ESPI and LV share a common reference arm, automatic heterodyning of the time-averaged ESPI fringes is achieved. The experimental results are described.