A fast-Fourier-transform method of topography and interferometry is proposed. By computer processing of a noncontour type of fringe pattern, automatic discrimination is achieved between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour-generation techniques. The method has advantages over moire topography and conventional fringe-contour interferometry in both accuracy and sensitivity. Unlike fringe-scanning techniques, the method is easy to apply because it uses no moving components.

Fourier-transform method of fringe-pattern analysis for computer-based topography and interferometry

We report on the development of the optical digital interferometry (ODI) technique for measuring diffusion and Soret coefficients. The unique feature of this method is that it traces the transient path of the system in the entire two-dimensional cross section of a cell. In this way, it is applicable not only for measurements of Soret coefficients, but also for studying diffusive transport mechanism and convection. Presently, this method is not widely used and, in our view, not because of fundamental limitations but rather due to a lack of properly developed postexperimental procedures of the raw data analysis. Thus, in this paper our attention is focused on the successive analysis of different steps: the fringe analysis, the choice of reference images, the thermal design of the cell, and multiparameter fitting procedure. Using the ODI technique, we have measured the diffusion and the Soret coefficients for three binary mixtures composed of dodecane (C(12)H(26)), isobutylbenzene, and 1,2,3,4-tetrahydronaphtalene at a mean temperature of 25(∘)C and 50 wt. % in each component. These measurements were compared with their benchmark values and show an agreement within less than 3%.

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Measurement of the Soret and diffusion coefficients for benchmark binary mixtures by means of digital interferometry.

We present an in-depth analysis of De Laval nozzles, which are ideal for gas jet generation in a wide variety of experiments. Scaling behavior of parameters especially relevant to laser-plasma experiments as jet collimation, sharpness of the jet edges and Mach number of the resulting jet is studied and several scaling laws are given. Special attention is paid to the problem of the generation of microscopic supersonic jets with diameters as small as 150 μm. In this regime, boundary layers dominate the flow formation and have to be included in the analysis.

Supersonic gas jets for laser-plasma experiments.

Using phase-measurement interferometry, we observe the waveguide induced by a solitonlike optical beam sustained by the molecular reorientation-induced optical nonlinearity of a nematic liquid crystal in planar configuration. Our purpose in the study is to characterize the nonlocality of the optical response of nematic liquid crystals. A good agreement is obtained between the experiment and a full (2+1)-dimensional numerical simulation of the nonlinear optical beam propagation in the cell.

P. Reiterer

Papers

Digital evaluation of interferograms