History and metrology applications of a game-changing technology: digital holography [Invited].

In digital holography (DH), information in the hologram is recorded and stored in digital format in discrete bits. Like its parent, holography, DH evolved over many years with periods of dormancy and revival. Almost abandoned, multiple times, unanticipated events or developments in separate industries revived it with explosive, quantum jumps, making it useful and popular to a wide audience.

Ultra-short pulsed off-axis digital holography for imaging dynamic targets in highly scattering conditions.

A single-shot digital holography system using an ultra-short pulsed laser is demonstrated to be very effective in suppressing the multiple-scattering noise associated with imaging dynamic targets in highly scattering environments, such as biological tissues and fuel injection systems. A planar off-axis reference wave configuration is used to generate a fixed carrier spatial frequency in the recorded holograms in order to separate coherent signal from incoherent noise in Fourier transformed holograms. The single-shot imaging system does not require averaging between multiple shots and can capture images of transient phenomena, such as the formation of diesel fuel injection sprays, and can overcome the problem of mechanical vibrations for recording holograms in industrial and laboratory environments.

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.

Design and preparation of a particle dynamics space flight experiment, SHIVA.

This paper describes the flight experiment, supporting ground science, and the design rationale for a project on spaceflight holography investigation in a virtual apparatus (SHIVA). SHIVA is a fundamental study of particle dynamics in fluids in microgravity. Gravitation effects and steady Stokes drag often dominate the equations of motion of a particle in a fluid and consequently microgravity provides an ideal environment in which to study the other forces, such as the pressure and viscous drag and especially the Basset history force.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.