Deformation reconstruction by means of surface optimization. Part II: time-resolved electronic speckle pattern interferometry.

An analysis of time-resolved electronic speckle pattern interferograms using an optimization algorithm is shown to provide full-field measurements of transient surface deformation. The arrangement uses a continuous-wave laser and high-speed camera to capture speckle images, with the recovery of the time-resolved deformation achieved by spatiotemporal processing using an optimization algorithm. It is shown that the process allows imaging of high-speed non-monotonic out-of-plane displacements with sub-micrometer amplitude. Time-resolved amplitude and phase recovery is demonstrated by analyzing the out-of-plane deformation of harmonic and transient events in a friction membranophone.

Deformation reconstruction by means of surface optimization. Part I: Time-averaged electronic speckle pattern interferometry.

Electronic speckle pattern interferometry is a well-known experimental technique for full-field deformation measurements. Although speckle interferometry techniques were developed years ago and are widely used for the visualization of the operating deflection shapes of vibrating surfaces, methods for accurate reconstruction of the observed deflection shape are still an active topic of research. Determination of the relative phase of the motion of vibrating objects is especially difficult and normally phase maps are calculated by direct transformation of the experimentally obtained interferometric images. An alternative method of phase reconstruction is described that involves solving the inverse problem via surface optimization. Compared to previously developed optimization methods, this method offers a higher spatial resolution and is more suitable for analysis of complex vibration patterns.

Methods of phase reconstruction for time-averaging electronic speckle pattern interferometry.

Electronic speckle pattern interferometry is useful for the qualitative depiction of the deformation profile of harmonically vibrating objects. However, extending the process to achieve quantitative results requires unwrapping the phase in the interferogram, which contains significant noise due to the speckle. Two methods to achieve accurate phase information from time-averaged speckle pattern interferograms are presented. The first is based on a direct inverse of the regions within corresponding phase intervals, and the second is based on optimization of four independent parameters. The optimization method requires less time than more commonly used algorithms and shows higher precision of the resulting surface displacement.