ABSTRACT
We report a specially designed adaptive mirror that can be bent into a helical shape for generation of an optical phase singularity. The adaptive helical mirror (AHM) reported here is a reflective device that can provide a continuous phase variation of the optical field in the azimuthal direction. The construction details and evaluation of the AHM are presented. A Michelson interferometer is used for the detection of the phase singularity. The AHM can be used for generation of a singular beam having multiple topological charges, positive or negative, just by controlling the excitation voltage of the AHM.
ABSTRACT
Digital speckle pattern interferometry (DSPI) and digital shearography (DS) are well known optical tools for qualitative as well as quantitative measurements of displacement components and its derivatives of engineering structures subjected either static or dynamic load. Spatial phase shifting (SPS) technique is useful for extracting quantitative displacement data from the system with only two frames. Optical configurations for DSPI and DS with a double aperture mask in front of the imaging lens for spatial phase shifting are proposed in this paper for the measurement of out-of-plane displacement and its first order derivative (slope) respectively. An error compensating four-phase step algorithm is used for quantitative fringe analysis.
ABSTRACT
We present a novel optical configuration that yields a fringe pattern that represents the slope changes of a three-dimensional object with a twofold increase in sensitivity. The method offers controllable sensitivity over a wide range. We accomplish it by modifying the in-plane displacement sensitive configuration of speckle interferometry. The detailed theory and the experimental results are presented with a brief discussion on the limiting aspects of the configuration.
ABSTRACT
A fringe-formation theory for a dual-beam illumination configuration that leads to a twofold increase in sensitivity for the measurement of in-plane displacement is described. Here we have taken into account all four beams simultaneously that are generated at the image plane owing to two-beam illumination and their cross-interference terms for fringe formation. We show that the sensitivity obtainable is the usual interferometric sensitivity when we take into account all four beams simultaneously and doubles only when the retroreflected beams are observed. A detailed theory and an experimental demonstration of the method are presented.
ABSTRACT
Hitherto no method, to our knowledge, was known to incorporate spatial phase shifting for the measurement of pure in-plane displacements. We demonstrate that the modified Duffy two-aperture configuration [Opt. Lett. 22, 1958 (1996)], which is sensitive to only the in-plane displacement component and offers increased sensitivity, lends itself to measurement with spatial phase shifting. The configuration can also be used for obtaining displacement derivatives by the introduction of shear with the tilt of a mirror.
ABSTRACT
The Ronchi grating is well known for its many applications in areas such as spectroscopy, grating interferometry, and Talbot interferometry. On the other hand, the checker grating has attracted very little attention. A checker grating also self-images at equidistant planes; the separation between these planes is a quarter of the Talbot distance of a Ronchi grating of the same period. To understand this and several other features, a transition from Ronchi grating (a one-dimensional grating) to checker grating (a two-dimensional grating) has been both theoretically and experimentally studied and results are presented. Because the checker grating self-images closer to the grating and its transmittance is higher than that of a Ronchi grating, the use of its self-image planes for array generation is also emphasized.
ABSTRACT
An optical configuration for measurement of in-plane displacement and for contouring is reported. In this method an object point is viewed symmetrically with respect to surface normal and combined coherently at the image plane of the imaging system. Because the beams are combined by small apertures at the image plane, decorrelation sets in rather slowly. Owing to low decorrelation, fringes have been obtained for large in-plane deformations and large angular tilts. The method is simple to implement, and its sensitivity can be varied over a wide range. The configuration, therefore, extends the range of measurement.
ABSTRACT
Multiaperture speckle shear interferometry exhibits sensitivity to in-plane displacement components. The response of the interferometer to in-plane displacement, however, depends on the location of the shear element on an aperture in front of the imaging lens. Two configurations with three apertures, with the shear element positioned at two different locations, are examined theoretically and experimentally.
ABSTRACT
We demonstrate the real-time image-processing operations of edge enhancement, theta filtering, and pattern recognition with a self-pumped phase conjugator with an external erase beam to modify the index gratings formed inside the photorefractive BaTiO(3) crystal.
ABSTRACT
We describe a modification of the wedge-plate shear interferometer for collimation testing. The surface of the wedge plate is coated to increase the reflectivity such that multiple-beam interference takes place resulting in sharp fringes. In addition to sharpening the fringes also tend to split when the test beam is noncollimated. This splitting has been used as a test criterion for collimation testing. Experimental results are presented.
ABSTRACT
Lateral shear interferometry is used to obtain the lateral aberrations of a lens. The zeroth-order fringe in an interferogram obtained from a wedge-plate lateral shear interferometer, however, directly displays the lateral aberration curve of a test lens. Nevertheless, the intensity distribution, is cosinusoidal. Multiple-beam interferometry results in sharpened fringes; hence the multiple-beam wedge-plate shear interferometer displays the lateral aberration curve of a lens sharply, provided the shear is small. For large shear, some new artifacts appear in the interferogram, which are also explained.
ABSTRACT
A modified configuration of the double-wedge-plate shearing interferometer for collimation testing is described. Results of the measurements to determine the setting sensitivity with this configuration are presented.
ABSTRACT
A comparative study of the performance of linear dual-field, spiral, and evolute gratings for collimation testing with Talbot interferometry is reported.
ABSTRACT
Some new configurations of a wedge-plate interferometer are described that use two wedge plates for collimation testing with a built-in reference unlike a single wedge plate for which an external reference is required. Theory and measurement results are presented.
ABSTRACT
An optical configuration is suggested that will achieve a twofold increase in sensitivity when one measures an in-plane displacement component of a deformation vector compared with the Leendertz two-beam illumination method. A theory and experimental demonstration of the method are presented.
ABSTRACT
We describe a simple method for measuring the radius of curvature by using Talbot interferometry in a noncollimated light beam. This scheme can also be used to determine the focal length of the collimating lens employed in the setup. Results of the measurements are presented. A discussion of achievable accuracies and the proper choice of parameters is included.
ABSTRACT
A new and simple technique for the determination of the focal length of positive lenses and concave spherical surfaces by Talbot interferometry is described. Results of measurements are presented. We show that high measurement accuracy can be achieved with this technique.
ABSTRACT
This Technical Note describes a method to measure the wedge angle of a beam splitter that relies on shear interferometry and the moire phenomenon.
