A digital holographic technique is implemented in a microscope for three-dimensional imaging reconstruction. The setup is a Mach-Zehnder interferometer that uses an incoherent light source to remove the coherent noise that is inherent in the laser sources. A phase-stepping technique determines the optical phase in the image plane of the microscope. Out-of-focus planes are refocused by digital holographic computations, thus considerably enlarging the depth of investigation without the need to change the optical focus mechanically. The technique can be implemented in transmission for various magnification ratios and can cover a wide range of applications. Performances and limitations of the microscope are theoretically evaluated. Experimental results for a test target are given, and examples of two applications in particle localization and investigation of biological sample are provided.

A quantitative autocalibrated high-resolution schlieren technique for quantitative measurement of reflective surface shape is proposed. It combines the schlieren principle with the phase-shifting technique that is generally used in interferometry. With an appropriate schlieren filter and appropriately tailored setup, some schlieren fringes are generated. After application of the phase-shift technique, the schlieren phase is calculated and converted into beam deviation values. Theoretical and experimental demonstrations are given. The technique is validated on a reference target, and then its application in a fluid physics experiment is demonstrated. These two examples show the potential of the phase-shifting schlieren technique that in some situations can become competitive with interferometry but with a much better dynamic range and with variable sensitivity. The technique can also be used to measure refractive-index gradients in transparent media.

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An integrated optical set-up for fluid-physics diagnostics is proposed. The combined diagnostic tools are direct visualization, the schlieren technique, electronic speckle-pattern interferometry, differential interferometry, digital holography and holographic interferometry with a photorefractive crystal. The sharing of most of the optical lenses allows a compactness of hardware compatible with space-application requirements (the Fluid Science Laboratory for the International Space Station). Performances and complementarity of techniques are discussed. Interferometric methods for refractive-index measurement are compared and preliminary experimental results are given.

We present a new optical deflection tomography method that takes advantage of the phase-shifting schlieren. The reconstruction algorithm is based on filtered backprojection. The instrument is well adapted for three-dimensional imaging of spatially sparse objects exhibiting large refractive index variations. It achieves a 35 μm resolution with a 3 mm depth of field. Its performance is illustrated with a bundle of fibers immersed in a matching index solution.

The fine atomization of liquids by means of low-frequency ultrasonic atomizers (about 50 kHz) results from unstable surface waves generated on the free surface of a thin liquid film. This thin liquid film develops as the liquid spreads fast over the atomizing surface of the atomizer. The displacement amplitude of the atomizing surface must be greater than 2 μm to initiate the atomization process. This may be achieved using a displacement amplitude transformer. The present study focuses on an analytical analysis of the longitudinal oscillations stimulated by the piezoelectric elements in a stepped horn which operates as an amplitude transformer. A sizing method of the stepped horn is established and experimentally tested. The influence of the materials’ mechanical damping on the displacement amplitude of the atomizing surface is investigated. The comparison between theoretical and experimental results allows the determination of the internal damping coefficient.

The dynamics of thermal ripples at the interface of a volatile pure liquid (C 2 H 5 OH) is studied experimentally and numerically. Liquid evaporates under a flow of inert gas (N 2 ) circulating along the interface. The evaporation rate is varied by regulating both the gas flow rate and the gas pressure. Experiments in microgravity environment allowed to identify a transition to "interfacial turbulence", along which some particular events such as nearly periodic and possible intermittent behaviors. Direct numerical simulations have been performed, and compare qualitatively well with experimental results, offering new insights into the physical mechanisms involved. Small-scale ripples appear to arise from a secondary instability of large-scale convection cells and their motion seems to follow the corresponding large-scale surface flow. The relative role of surface tension and buoyancy in triggering these flows is assessed by comparing experiments and simulations in both microgravity and ground conditions. Qualitative features compares satisfactorily well such as typical speed and orientation of the thermal ripples, as well as spiral flow in the bulk.