Vanusch Nercissian

Parallel two-step phase-shifting point-diffraction interferometry for microscopy based on a pair of cube beamsplitters

Parallel two-step phase-shifting point-diffraction interferometry for microscopy based on a pair of cube beamsplitters is proposed. The first 45°-tilted cube beamsplitter splits object wave into two parallel copies: one copy is filtered by a pinhole in its Fourier plane to behave as reference wave, while the other one remains unchanged as object wave. The second cube beamsplitter combines the object and reference waves, and then split them together into two beams. Along with the two beams, two parallel phase-shifting interferograms are obtained in aid of polarization elements. Based on the proposed configuration, slightly-off-axis interferometry for microscopy is performed, which suppresses dc term by subtracting the two phase-shifting holograms from each other. The setup is highly stable due to its common-path configuration, and has been demonstrated to be suitable for measuring moving objects or dynamic processes.

Phase-shifting point-diffraction interferometry with common-path and in-line configuration for microscopy.

A new common-path and in-line point-diffraction interferometer for quantitative phase microscopy is proposed. The interferometer is constructed by introducing a grating pair into the point-diffraction interferometer, thus forming a common-path and in-line configuration for object and reference waves. Achromatic phase shifting is implemented by linearly moving one of the two gratings in its grating vector direction. The feasibility of the proposed configuration is demonstrated by theoretical analysis and experiments.

Diffractive simultaneous bidirectional shearing interferometry using tailored spatially coherent light

Measurements of wavefront deformations can be carried out with the help of lateral shearing interferometers. Here the focus is on a setup providing two shears along orthogonal directions simultaneously to generate the data needed for a reconstruction. We describe a diffractive solution using Ronchi phase gratings with a suppressed zeroth order for both the doubling of the wavefront under test and the bidirectional shearing unit. A series arrangement of the gratings offers an on-axis geometry, which minimizes the systematic errors of the test. For illumination, an extended incoherent monochromatic light source is used. High-contrast fringes can be obtained by tailoring the degree of coherence via a periodic intensity distribution.

Evaluation algorithms for multistep measurement of spatially varying linear polarization and phase.

Optical components manipulating both polarization and phase of wave fields find more and more applications in todays optical systems. In particular, the polarization orientation may vary across the aperture. New measurement techniques and evaluation algorithms are needed to simultaneously characterize the properties of such elements. In this Letter, a general measurement algorithm for locally linear polarization distributions is presented, extending the methods of phase shifting interferometry to the simultaneous determination of polarization and phase. A class of evaluation algorithms is derived, and some example algorithms are described and tested for their resilience against systematic and stochastic stepping errors.

Simultaneous measurement of phase and local orientation of linearly polarized light: implementation and measurement results

Optical components manipulating both polarization and phase of wave fields find many applications in todays optical systems. With modern lithography methods it is possible to fabricate optical elements with nanostructured surfaces from different materials capable of generating spatially varying, locally linearly polarized-light distributions, tailored to the application in question. Since such elements in general also affect the phase of the light field, the characterization of the function of such elements consists in measuring the phase and the polarization of the generated light, preferably at the same time. Here, we will present first results of an interferometric approach for a simultaneous and spatially resolved measurement of both phase and polarization, as long as the local polarization at any point is linear (e.g., for radially or azimuthally polarized light).

Mass transfer of organic substances in supercritical carbon dioxide

In this work special attention is paid on the direct visualization of the diffusion process of oil droplets in supercritical carbon dioxide as well as better characterization of the process by quantitatively evaluating the important parameter - the diffusion coefficients obtained with a shearing interferometer. Experiments are also to be carried out under microgravity to improve the experiment condition where the influence of gravity-driven convection that usually dominates the transport process is minimized.

Reduction of phase singularities in speckle-shearing interferometry by incoherent averaging of speckle patterns

Speckle interferometry is a well established technique for the optical characterization of rough objects, with the quantification of deformations as one particular application of interest. Owing to its common path property, a speckle-shearing interferometer is often the natural choice as a setup. Like other speckle techniques, however, speckle-shearing interferometry suffers from the existence of phase singularities present in the speckle patterns. Phase singularities introduce ambiguities into the phase unwrapping process and make this evaluation step highly sophisticated. In this work, we attempt to reduce the number of phase singularities by physical means, i. e. by applying an incoherent averaging of multiple, mutually independent speckle intensities. The effect of the incoherent averaging on the number of phase singularities has been investigated theoretically, by computer simulations, and experimentally. To obtain high contrast fringes in connection with a shearing setup, which would not be the case for a simple extended light source, a periodically structured light source with a period matched to the shear distance is applied. It turns out that the number of phase singularities may indeed be reduced, but only to a certain extent.

Phase and Polarization Measurement of a Spatially Varying Linear Polarization Distribution

Optical components manipulating both polarization and phase of wave fields find a lot of applications in today’s optical systems. It is possible to fabricate optical elements with nanostructured surfaces for the generation of any orientation of locally linearly polarized light [1]. The wave front of a radial polarizer made from a subwavelength aluminium radial grating on a glass substrate for the wavelength λ=633nm was measured. This optical element generates an additional phase term together with the desired polarization distribution [2].

Mass Transfer of Organic Substances in Supercritical Carbon Dioxide

In this work special attention is paid on the direct visualization of the diffusion process of oil droplets in supercritical carbon dioxide as well as a better characterization of the process by quantitative evaluation of the diffusion coefficients obtained with a shearing interferometer. Experiments are also to be carried out under microgravity in to improve the experiment condition where the influence of gravity-driven convection that usually dominates the transport process is minimized.

Diffractive simultaneous lateral shearing interferometry

A lateral shearing interferometer usually provides the slope data of a wave front under test along one direction. For the complete reconstruction of the wavefront, two slope datasets along different directions are required. Based on diffractive gratings, a simultaneous measurement of bothdata sets can be carried out. Two possible realizations are presented using a polarization signature and a partially coherent light source.