Phase-shifted Interferograms Research Articles

Vibration Measurement Using Phase-shifting Stroboscopic Holographic Interferometry

A fringe-evaluation system for a vibration measurement is presented, which is based on the phase-shifting method in real-time holographic interferometry. Phase-shifted real-time holographic interferograms are acquired by a TV camera when stroboscopically illuminating the object of interest. An arctangent calculation with phase-shifted fringe patterns gives a phase distribution proportional to the displacement of the object, including the initial phase of the vibration. The effects of the time-integration of the real-time fringe, which involves a reduction in fringe contrast and phase error in the arctangent calculation, are analysed theoretically. Experimental demonstrations are also presented for two cases: vibration which is spatially uniform; and vibration in which the initial phase is non-uniform.

Fringe scanning speckle-pattern interferometry

Digital speckle-pattern interferometry systems for automatic measurement of deformations of a diffuse object are presented, which are based on a fringe scanning method with phase-shifted speckle interferograms. A digital speckle pattern before deformation of an object is recorded in the mass storage device of a computer facility. After deformation, four digital speckle patterns are recorded as changing the phase of reference light such as 0, π/2, π, and 3π/2, respectively. Four speckle interferograms, whose phases are shifted by 0, π/2, π, and 3π/2, are generated by calculating the square of the differences between speckle patterns before and after deformation. These interferograms are low-pass filtered to reduce speckle noise. The calculation of the arctangent with four phase-shifted speckle interferograms gives the optical path difference which is proportional to the deformation. A correction of the discontinuity of the calculated phase gives the numerical data of the deformation in the whole object area. Some experimental results for the measurement of out-of-plane, in-plane, and 3-D deformations are presented.