R.S. Sirohi

Achromatic phase shifting by a rotating polarizer

We describe here an achromatic phase shifting arrangement based on polarization components in which the phase shifting is obtained by rotating a polarizer. These can be used in a polarization interferometer to introduce variable phase shift that is independent of wavelength.

Improved techniques of collimation testing

Abstract Improved techniques of collimation testing based on Talbot imaging and shearing interferometry are presented. The proposed techniques carry their own reference pattern to indicate collimation of the light beam. Detailed analysis is also given.

Direct determination of focal length by using Talbot interferometry

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.

Separation of the influence of in-plane displacement in multiaperture speckle shear interferometry

An imaging system with its aperture fully open or with a multiaperture mask in front has been used for carrying out speckle shear interferometry. The shearing is achieved by installing shear elements in front of the imaging system. The multiaperture configuration has built-in in-plane displacement sensitivity, and hence shear fringes obtained from multiaperture shear interferometer always carry the in-plane displacement contribution. This problem does not arise when the full aperture of the lens is used. A three-aperture speckle shear interferometric technique is introduced here to separate the in-plane displacement and slope contributions from the shear interferogram. Detailed theoretical and experimental results are presented.

Self-referencing collimation testing techniques

Self-referencing collimation testing techniques are briefly reviewed. New self-referencing configurations using Talbot and doublewedge plate shear interferometric techniques are described. Setting sensitivities of various arrangements are compared.

Talbot interferometry in noncollimated illumination for curvature and focal length measurements

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.

Setting sensitivity in Talbot interferometry with modified gratings

Abstract A dual field grating has been introduced for use in Talbot interferometry. We report here results of an experimental investigation on setting sensitivity when using these gratings for testing.

An Ellipsometric Study of Chromium Passivation

In situ ellipsometry has been combined with electrochemical measurements to gain insight into the mechanism of passivation of chromium in pH 1.7 solution. At −410 mV vs. NHE a region of active dissolution at an apparently oxide‐free surface was observed. With an anodic potential step to −360 mV, passivation occurs with growth of less than 1Aa of oxide film. This film is thicker at more anodic potentials and probably consists of .The mechanism of passivation most consistent with the experimental observations is that of simultaneous oxide formation and metal dissolution, with passivation resulting from formation of a monolayer of film.

Speckle and speckle-shearing interferometers combined for the stimultaneous determination of out-of-plane displacement and slope

Speckle and speckle-shearing interferometer geometries have been combined into a single setup by the use of a small ground glass reference diffuser on the lens pupil. Sheared fields are obtained with a split lens arrangement. Judicious aperturing results in separated diffraction halos at the FT plane. Fringe patterns corresponding to out-of-plane displacement and slope are obtained by filtering via the appropriate halos. A four-aperture arrangement coupled with shearing elements extends the method to obtain the moire curvature pattern.

Double-wedge-plate interferometer for collimation testing : new configurations

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.