Geometry for contouring by electronic speckle pattern interferometry based on shifting illumination beams

From speckle pattern photography to digital holographic interferometry [Invited]

Speckles are inherently an interference phenomenon produced when an optically rough surface or a turbulent medium introduces some degree of randomness to a reflected or a transmitted electromagnetic field. Speckles are often nuisance in coherent image formation. Speckle patterns are however a useful tool for displacement and deformation as well as vibration and stress analysis. The development of speckle photography to speckle interferometry and digital holographic interferometry is described in this paper.

Shape and deformation measurements of 3D objects using volume speckle field and phase retrieval

Shape and deformation measurement of diffusely reflecting 3D objects are very important in many application areas, including quality control, nondestructive testing, and design. When rough objects are exposed to coherent beams, the scattered light produces speckle fields. A method to measure the shape and deformation of 3D objects from the sequential intensity measurements of volume speckle field and phase retrieval based on angular-spectrum propagation technique is described here. The shape of a convex spherical surface was measured directly from the calculated phase map, and micrometer-sized deformation induced on a metal sheet was obtained upon subtraction of the phase, corresponding to unloaded and loaded states. Results from computer simulations confirm the experiments.

Application of dynamic phase shifting with wavelet analysis to electronic speckle contouring

Dynamic phase shifting is a temporal phase unwrapping method, i.e., a method in which a sequence of speckle patterns is analyzed along the time axis. Each pixel can thus be considered as an independent detector, which is of particular interest for the study of complex surfaces. I report the application of this technique, which is based on a wavelet analysis, to contouring measurements with a dual-beam illumination electronic speckle pattern interferometry setup. I present a new, more general geometric model of the setup. I also investigate the possibility of enhancing the accuracy by using the intermediate phase values. Tests are performed on a simply described object and compared with coordinate measuring machine measurements.

Speckle decorrelation in surface profilometry by wavelength scanning interferometry

The accuracy and the measurement range of surface profilometry by wavelength scanning interferometry applied to diffusely reflecting surfaces are investigated. The influences of surface roughness and the imaging system in the interferometer are theoretically analyzed by derivation of the autocorrelation function of interferograms arising from wavelength scanning. By using a dye laser with a tuning range of 4.2 nm to a yield resolution of 39.1 mum, we have observed interferograms and their Fourier transforms and autocorrelations to study effects of defocusing and the size ratio of speckle to the CCD pixel for a plane diffuse object positioned normal to the incident beam.

Contouring by electronic speckle pattern interferometry with quadruple-beam illumination

We present a new arrangement for contouring by electronic speckle pattern interferometry with four illumination beams, thereby making it unnecessary to move anything during the.