Double exposure holographic interferometry

Double exposure holographic interferometry is a tool widely employed for vibration analysis. Here holography principle is suitably applied to interferometry. When an object moves during an exposure to light, a series of images will be recorded with intensity proportional to the length of time spent in each position. This principle is utilized here. When the zero order Bessel function becomes zero, the amplitude of vibration yields a dark band. Fixed boundaries and nodal lines appear as bright bands since amplitude of vibration there is zero. Because of zero order Bessel function, fringe contrast decreases rapidly with fringe order. This is a serious cause of concern. You can minimize this by keeping the exposure time to minimum. Generally, it is very difficult to observe more than 15 fringes.