Phase-shifting Speckle Pattern Interferometry Research Articles

Speckle interferometry for measurement of continuous deformations

Improvements of a method for measurement of continuous displacements and deformations with digital phase shifting speckle pattern interferometry are presented. The method is based on an algorithm that, with the knowledge of the initial phase, only needs one image at a time to evaluate continuos phase changes due to object deformations. In the improved method, the initial random phase of the speckle pattern is evaluated using a number of phase-shifted images before the deformation under study. This is used for increasing the accuracy of the initial phase estimation and reducing influences from image noise and other measurement disturbances. The phase-shifted speckle patterns are used as references for comparison with the speckle patterns of the deformed object, thereby increasing the reliability and accuracy of the phase estimations of the deformed patterns. The technique can be used for measuring deformations such as transients and other dynamic events, heat expansion as well as other phenomena where it is difficult to accomplish phase shifting during deformation.

Phase errors in low-frequency vibration measurement with high-speed phase-shifting speckle pattern interferometry

When mechanical vibrations are measured by means of a dynamic phase-shifting speckle pattern interferometer, the deformation can be tracked with an error that depends on the amplitude and frequency of the vibration. We use a numerical simulation based on a detailed mathematical model of the system to predict the expected frequency response of the root mean square (rms) measurement error in the time-varying phase difference maps. The performance of four phase- shifting algorithms (three-frame, four-frame, Carre, and Schwider- Hariharan five-frame) and a temporal phase unwrapping method is studied over a range of vibrational amplitudes and frequencies. The numerical results indicate that the Carre algorithm is the preferred phase-shifting method to measure vibrations with a dynamic electronic speckle pattern interferometry (ESPI) system. Vibration frequencies up to 30% of the carrier frequency can be measured with an rms phase change error less than l0% of the vibration amplitude. The numerical results are finally compared with experimental data, acquired using a 1000 frame/s phase-shifting speckle interferometer together with a laser vibrometer, which provides a reference phase measure.

Phase-shifting speckle interferometry: a noise reduction filter for phase unwrapping

We present a noise reduction filter for the phase unwrapping of data from phase-shifting speckle pattern interferometry. This filter is effective in reducing the noise in wrapped phase maps without affecting the edges of the phase jumps, so that a simple and fast unwrapping algorithm can be used. We also discuss a data analysis strategy, includ- ing a routine for the recovery of unwrapping errors. The filter perfor- mance has been evaluated on real data from a fiber optic phase-shifting speckle interferometer, which we built for the analysis of out-of-plane deformations. The phase shifting is introduced by current modulation of the diode laser source. Some results relative to the analysis of very noisy phase measurements are presented. © 1997 Society of Photo-Optical Instru- mentation Engineers. (S0091-3286(97)01209-9)