Guillermo H. Kaufmann

An analysis based on the comparison between singularities of speckle phase and pseudophase in the practice of optical vortex metrology is carried out by measuring the phase map of the speckle pattern obtained from the transmitted light through binary diffusers. In the characterization of the core structure of both phase singularities, the variation of the measured parameters is produced by means of in-plane linear displacements and rotations of the scattered speckle fields. These fields are addressed by using similar displacements of the binary phase masks recorded in a spatial light modulator (SLM). We complete these comparisons by measuring out-of-plane variations of the core structure parameters. In addition, we verified that the phase map of the transmitted light beam through the binary diffusers recorded in SLMs is actually characterized by a speckle phase with vortices of unitary charge. The presented analysis would be helpful for understanding the scope and limitations of the use of the singularities of speckle phase and pseudophase as position marking, and also for speckle measurement of in-plane rigid-body displacements of binary diffusers dynamically controlled by means of SLMs.

This paper presents the evaluation of a removal method to cancel the thermal convection effect that is generated in vertically positioned metal plates loaded by thermal waves when a lock-in temporal speckle pattern interferometry technique is used to detect hidden flaws. Additionally, the resolution of this technique to detect two nearby flaws is also analyzed.

We present the application of a portable radial in-plane speckle interferometer to the measurement of residual stresses when local heating is used as a stress relaxation technique. We also present a numerical method to calculate the residual stresses from the radial in-plane displacement field that is measured subsequent to the heating and cooling of the interrogated spot. A finite element analysis of the thermomechanical response of the specimen under test is performed to adjust the model used for residual stress determination. To evaluate the performance of this technique, results obtained using several preloaded specimens are compared with the stress introduced in them. It is shown that the speckle interferometer and local heating combined system allows the measurement of residual stresses with an average deviation of approximately 7% for a range of uniaxial stresses from 25 up to 75% of the yield stress of the material.

A temporally modulated IR lamp is employed to heat the surface of a flawed plate and the resulting out-of-plane thermoelastic deflection is monitored using phase-shifted temporal speckle pattern interferometry. The speckle interferograms are continuously recorded by means of a high-speed digital camera with temporal phase shifting carried out by a Pockels cell synchronized with it. Temporal phase unwrapping through sequences of several hundreds of frames enables the determination of time-varying absolute displacement maps. Experimental results illustrate the possibilities of this novel nondestructive testing technique. © 2003 Society of Photo-Optical Instrumentation Engineers.

We present an evaluation of the continuous wavelet transform method when it is used to measure the phase distribution encoded by electronic speckle pattern interferometry (ESPI) fringes. The evaluation is performed using computer-simulated fringes, an approach that allows knowing precisely the phase map contained in the pattern. It is shown that only ESPI fringes that verify the stationary phase approximation and its analytic asymptotic limit can be analyzed with the continuous wavelet transform method. The influence of the filtering process to smooth the ESPI fringes and the method used to extend the fringe pattern edges is also analyzed. Finally, additional drawbacks that emerge when this phase evaluation method is applied are discussed. © 2002 Society of Photo-Optical Instrumentation Engineers.

This paper presents a comparative study of different thresholding methods for speckle noise reduction in electronic speckle pattern interferometry fringes using several wavelet bases. An approach based on the removal of the wavelet subbands of the transformed image is presented. The performance of this method is analyzed and compared with the results obtained with the denoising techniques that use wavelet shrinkage. It is shown that the wavelet subband removal method reduces speckle noise and maintains image features more effectively than the wavelet shrinkage techniques based on soft and hard thresholding. © 2001 Society of Photo-Optical Instrumentation Engineers.

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.

Single pulsed subtraction electronic speckle-shearing pattern interferometry is used to measure the time evolution of deformations induced by periodic impulse loading on a metal plate. This is accomplished with a stroboscopic system based on a pulsed laser and an interline-transfer CCD camera running at 60 frames/s. In a few seconds, a sequence of hundreds of interferograms is recorded with an effective sampling time interval of some tens of microseconds. We describe the experimental setup used to generate the transient deformation on the metal plate and also the synchronization of laser pulses and image acquisition. Several correlation fringe patterns are presented, showing the time evolution of the deformation. Finally, these data are used to calculate optical phase maps and displacement derivative fields for different times after the application of the dynamic load on the object.

We report a technique for the measurement of transient outof- plane displacement gradients in plane objects by double-pulsed subtraction TV shearography. The fringe patterns are automatically and quantitatively analyzed by the Fourier transform method. A novel optical setup based on the separation and further recombination of illumination beams is demonstrated for the generation of carrier fringes. The principle of the proposed technique is theoretically described, and its immunity to environmental disturbances is discussed. Experimental results obtained with a metallic plate excited by the impact of a piezoelectric transducer are presented.

A technique for increasing the displacement measurement range in electronic speckle-shearing pattern interferometry is proposed. The technique is based on the introduction of carrier fringes and the use of a temporal-phase-unwrapping method to obtain larger measuring ranges of out-of-plane displacements of an object without sign ambiguities. A larger measuring range is obtained by dividing the desired maximum-phase range into several subranges where the spatial synchronous detection method can be successfully applied. These phase subranges correspond to small out-of-plane displacements of the object, and a speckle pattern is recorded for each displacement. The carrier fringes are obtained by the subtraction correlation of two consecutive speckle fields with a translation of the illuminating beam between recordings. The method allows the measurement of object displacements of about 216 μm. © 2000 Society of Photo-Optical Instrumentation Engineers.