Generalized method for wave-front analysis

Surface measurements by white light spatial-phase-shift imaging interferometry

A novel method of common-path imaging interferometry, the White Light Spatial-Phase-Shift (WLSPS) for object surface measurements, is discussed here. Compared to standard White Light Interferometry (WLI), which uses a reference mirror, the interferometry of WLSPS is obtained by creating manipulations to the light wavefront reflected from an object's surface. Using this approach, surface measurements can be obtained from any real object image, and do not need to be taken directly from the object itself. This creates the ability for a surface measurement tool to be attached to any optical system that generates a real image of an object. Further, as this method does not require a reference beam, the surface measurement system contains inherent vibration cancelation.

Phase mapping and wavefront analysis based on multi-illumination light fields generated by a spatial light modulator

We present a new multi-illumination technique for the determination of the phase maps of unknown phase objects and wavefronts based on their diffraction patterns. A spatial light modulator is used to generate a sequence of probe-light fields that illuminate the unknown object producing different diffraction patterns. Compared with similar diffraction-pattern-based approaches, our technique benefits from a motionless multiview operation and a significantly improved deconvolution algorithm convergence speed (tens of iterations versus hundreds). Computer simulations indicate that the extra information brought by the different diffraction patterns prevents convergence of the phase retrieval algorithm to spurious local minima solutions and results in faster convergence. We describe an experimental system built based on our approach using readily available, relatively low-cost components. Successful reconstructions of test targets from experimental diffraction patterns confirm the feasibility of the technique. Major sources of error are identified, solutions to these problems suggested, and potential extensions to multiresolution analysis of unknown wavefronts are proposed.

Wavefront reconstruction by spatial-phase-shift imaging interferometry

Common-path imaging interferometers offer some advantages over other interferometers, such as insensitivity to vibrations and the ability to be attached to any optical system to analyze an imaged wavefront. We introduce the spatial-phase-shift imaging interferometry technique for surface measurements and wavefront analysis in which different parts of the wavefront undergo certain manipulations in a certain plane along the optical axis. These manipulations replace the reference-beam phase shifting of existing interferometry methods. We present the mathematical algorithm for reconstructing the wavefront from the interference patterns and detail the optical considerations for implementing the optical system. We implemented the spatial phase shift into a working system and used it to measure a variety of objects. Measurement results and comparison with other measurement methods indicate that this approach improves measurement accuracy with respect to existing quantitative phase-measurement methods.

Spatial phase-shift interferometry--a wavefront analysis technique for three-dimensional topometry

We describe a new wavefront analysis method, in which certain wavefront manipulations are applied to a spatially defined area in a certain plane along the optical axis. These manipulations replace the reference-beam phase shifting of existing methods, making this method a spatial phase-shift interferometry method. We demonstrate the system's dependence on a defined spatial Airy number, which is the ratio of the characteristic dimension of the manipulated area and the Airy disk diameter of the optical system. We analytically obtain the resulting intensity data of the optical setup and develop various methods to accurately reconstruct the inspected wavefront out of the data. These reconstructions largely involve global techniques, in which the entire wavefront's pattern affects the reconstruction of the wavefront in any given position. The method's noise sensitivity is analyzed, and actual reconstruction results are presented.