Multilayer volume holographic optical memory.

We demonstrate a scheme for volume holographic storage based on the features of shift selectivity of a speckle reference-wave hologram. The proposed recording method permits more-efficient use of the recording medium and yields greater storage density than spherical or plane-wave reference beams. Experimental results of multiple hologram storage and replay in a photorefractive crystal of iron-doped lithium niobate are presented. The mechanisms of lateral and longitudinal shift selectivity are described theoretically and shown to agree with experimental measurements.

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.

Sandwich, double-reference-wave, holographic, phase-shift interferometry.

Phase-shift interferometry has provided a straightforward method for converting interferograms to phase maps. Unfortunately, some of the most powerful pulsed holographic interferometry techniquesare generally not compatible with phase-shift interferometry. One solution is to employ two reference waves, one for each of the two object waves to be interfered, that can be phase stepped during reconstruction. Practical aberration and alignment problems render this approach difficult. A simple method that employs a second hologram, sandwiched with the first, which produces the required two reference waves during reconstruction, is presented. The process compensates for both chromatic and geometric aberrations that otherwise render the phase-shift method unusable.

The clinical education of primary care nurse practitioner students.

Directors of 112 ambulatory care nurse practitioner (NP) programs were surveyed to determine the amount and characteristics of the clinical education of their students. The response rate was 53%. Among all programs, students experienced an average of 597 clinical hours. This number was somewhat higher among family and women's health nurse practitioner programs. The range was large--192 to 1600 hours--however, eliminating both extremes left a majority of programs within a much narrower range; the central 62% of programs were between 400 and 700 hours. Certificate programs reported more hours than did masters programs. Almost all hours were in ambulatory settings, which included a wide mixture of public and private settings. A majority of students experience part of their clinical training along with medical residents and medical students, and often with NP students from other programs and with physician assistant students. Most NP program directors find these other disciplines' programs cooperative, and the NP directors favor stronger relationships.

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.

Application of generalized phase control during reconstruction to flow visualization holography.

Multiple exposure holograms can be produced with individual control over the phase of the reconstructed images. This can be achieved by controlling the appropriate phase of reference or object waves during either recording or reconstruction. When this procedure is used, many useful effects can be created in flow visualization holography. These include improved sensitivity and SNR. In this paper, the theory and techniques are developed for the method, and examples are given to illustrate such effects.

Coal particle combustion studied by holography.

The application of holography to the study of burning coal particles in free flight was examined. Resolution to about 3 microm was attained in the combustion zone of a flat flame burner. Both size and velocity of particles up to 75 microm in diameter were measured holographically. Holographic interferometry was also used. Basic combustion events in coal were recorded and are presented here which have not been observed previously. A comparison of images produced by in-line and off-axis holography also resulted from the study.

Resolution factors in edgeline holography.

When an in-line Fresnel hologram of an object such as a projectile in flight is made, the reconstruction comprises an image of the outside edge of the object superimposed upon a Fresnel diffraction pattern of the edge and an unmodulated portion of the reconstruction beam. When the reconstructed image is bandpass filtered, the only remaining significant contribution is that of a diffraction pattern which is symmetrical about an edgeline gaussian image of the object. The present paper discusses the application of this type of holography in accurately locating the edge of a large dynamic object, the position of which is not accurately known in any dimension. A theoretical and experimental analysis was performed to study the effects of motion, hologram size, film type, and practical limitations upon the attainable resolution in the reconstructed image. The bandlimiting effect of motion is used to relate the motion effected resolution limit of holography to that of photography. The study shows that an edgeline can be accurately located even at high velocity normal to the edge.

Holographic techniques for the study of dynamic particle fields.

The techniques of small particle holography are extended in an elementary way to show that multiple exposure holography can be used to study the dynamic properties of particle fields. Experimental techniques for performing such a study are then described. Finally, as a typical example, a multiple exposure hologram of an aerosol is presented with a portion of the data extracted from it. The hologram exhibits a vast amount of information including the determination of the velocity and density field, size distribution, flow structure, and diffusion rate.

Holographic color schlieren.

A 20-in (51-cm) diam schlieren system was convereted to a genrualized holographic flow visualization system. The system has been used successfully in producing the following types of visualization from a single holographic plate: three-dimensional photography, variable focus shadowgraph, variable knife-edge position schlieren, color-schlieren, and interferometry. All of these except for holographic color schlieren have previously been reported with varying degrees of success. This paper presents a technique for producing color schlierent photographs from holograms formed in the above system and shows preliminary results of the application. The method possesses a number of advantages over conventional color schlieren photography.