Chemical silver coating of fiber tips in near-field scanning optical microscopy.

We report what is believed to be the first experimental demonstration of silver coating by a wet chemical process on tapered fiber tips used in near-field scanning optical microscopy. The process occurs at room temperature and pressure and takes only a few minutes to complete. Many tips can be coated simultaneously.

Holographic particle-image velocimetry in the first International Microgravity Laboratory aboard the Space Shuttle Discovery.

In January 1992 the Space Shuttle Discovery carried the first International Microgravity Laboratory into Earth orbit for eight days. One of the many experiments carried out during the orbit was a combined study of triglycine sulfate crystal growth from solution and fluid-particle-dynamics studies in microgravity. Optical diagnostics included holocameras to provide concentration measurements and three-dimensional particle tracking. More than 1000 holograms that were recorded in space have been analyzed since the flight, providing a wide range of interesting conclusions about microgravity, crystal growth, and particle dynamics. This paper focuses on the results of holographic particle-image velocimetry experiments and provides an excellent example, along with new techniques, for exploiting holography for particle and flow diagnostics.

Continuous-wave laser beam fanning in organic solutions: a novel phenomenon.

If a low-power cw Ar(+) laser beam (~50 mW) is sent horizontally and focused on the entrance side of a cuvette containing an absorptive solution, the beam fans into the lower half of the cuvette instead of propagating through and forming self-phase-modulation fringes. We call this phenomenon self-beam fanning, which has been observed in several organic solutions. We present here several experimental results and a descriptive model of the phenomenon.

Algorithm for phase-difference measurement in phase-shifting interferometry.

A phase-shifting algorithm is proposed and experimentally demonstrated for phase-difference analysis. The method involves only three steps, the original and two equal in amount but unknown phase steps for each stage. Only six frames of data are thus sufficient for the phase-difference analysis between two stages. Real-time holographic interferometry with a concentration change in a sugar-water solution in a test cell is presented for experimental verification.

Determination of refractive properties of fluids for dual-wavelength interferometry.

Methods to calculate the refractive properties of solutions at different wavelengths are described by using experimental data at just two wavelengths. The properties are the refractive index and its gradients with temperature and concentration. Cauchy's equation is used to determine the refractive indices. The gradients versus temperature and concentration are then determined by using the Murphy-Alpert and the Lorentz-Lorenz equation, respectively. Finally, the particular case of a triglycine sulfate aqueous solution is considered as an example. The approach should provide the desired information for fringe analysis when dual-wavelength holographic or other interferometry is used for solving heat and mass transfer problems in fluids during crystal-growth experiments.

Reconstruction techniques of holograms from Spacelab 3.

Fluid transport effects in a ground-based laboratory are fairly well known. Bouyancy driven transport occurs when there is a local density change in the fluid. In a low-g environment these density changes become less important, and other transport mechanisms dominate. To better understand fluid flows in a low-g environment, a fluid experiment system (FES) was designed to fly aboard the Shuttle orbiter in Spacelab. The FES is a holographic system designed for acquisition of the maximum amount of data from an experiment. The FES flew for the first time in May 1985 on Spacelab 3 for investigation of triglycine sulfate (TGS) crystal growth in low-g. This paper describes the FES optical system. The reconstruction techniques of the holograms are examined in detail, and the multiuser and reflight capabilities are discussed. Proposed future experiments are mentioned.

Results and further experiments using Spacelab holography.

Spacelab 3 provided the platform for the first extensive application of holography in space. Holograms of excellent quality were recorded during the flight, providing information on the solution growth of triglycine sulfate crystals under microgravity conditions. The suppression of convection and the development of a symmetric concentration depletion region around each crystal were clearly shown. Crystal growth was governed by diffusion mass transport across the depletion region. The successful performance of the holographic unit has prompted NASA to schedule a slightly modified version for reflight on IML-1; opportunities now exist for other investigators to use this facility.