Vibration measurement using spatial shifting coherent digital holography

In this research, we proposed a new digital coherent holographic configuration for accurately measuring the three-dimensional (3D) vibration of the object. The vibration was indirectly measured by the displacement of the three mirrors attached on the object. The hologram recorded by the camera consisting of 6 sub-holograms can be separated by Fourier transform and appropriated spatial band-pass filters. Three phase sets extracted from 3 sub-holograms of the reference mirror and 3 object mirrors were used to calculate the displacement of the object in 3D directions. The relation between the displacement of the object and the phases of the sub-holograms was related to the wavelength of the light source, therefore this allows observing the vibration of the object with nano-scale accuracy in z direction and much smaller than the pixel size of the camera accuracy in x and y directions.