Use Of Holography Research Articles

Photopolymer holographic recording material

Photopolymers are promising materials for use in holography. They have many advantages, such as ease of preparation, and are capable of efficiencies of up to 100%. A disadvantage of these materials is their inability to record high spatial frequency gratings when compared to other materials such as dichromated gelatin and silver halide photographic emulsion. Until recently, the drop off at high spatial frequencies of the material response was not predicted by any of the diffusion based models available. It has recently been proposed that this effect is due to polymer chains growing away from their initiation point and causing a smeared profile to be recorded. This is termed a non-local material response. Simple analytic expressions have been derived using this model and fits to experimental data have allowed values to be estimated for material parameters such as the diffusion coefficient of monomer, the ratio of polymerisation rate to diffusion rate and the distance that the polymer chains spread during holographic recording. The model predicts that the spatial frequency response might be improved by decreasing the mean polymer chain lengths and/or by increasing the mobility of the molecules used in the material. The experimental work carried out to investigate these predictions is reported here. This work involved (a) the changing of the molecular weights of chemical components within the material (dyes and binders) and (b) the addition of a chemical retarder in order to shorten the polymer chains, thereby decreasing the extent of the non-local effect. Although no significant improvement in spatial frequency response was observed the model appears to offer an improved understanding of the operation of the material.

Update on the Use Of Holography for Optics And Photonics Education

Update on the Use Of Holography for Optics And Photonics Education

Holographic optical data storage

The evolution of holographic optical memories has followed a path not altogether different from holography itself. P.J. van Heerden is widely credited for being the first to elucidate the principles behind holographic data storage in a 1963 paper. The science and engineering of such a storage paradigm were heavily pursued thereafter. This resulted in many novel holographic multiplexing techniques for dense data storage and advances in holographic recording materials. Despite this progress, without technologies such as compact laser sources and optical data I/O devices, hope diminished for viable commercial products. Successful use of holography in other arenas rekindled interest in holographic data storage in the late 1980s. With many critical optoelectronic device technologies now in place, holography is once again considered a possible data storage solution.

Use of holography in particle image velocimetry measurements of a swirling flow

Particle Image Velocimetry (PIV) is now a well established experimental technique to measure two components of the velocity in a planar region of a flow field. This paper shows how its proven capabilities can be further extended by using holographic recording to register the particle displacements. Among other unique characteristics, holography enables the acquisition of multiple images on a single plate, and the recording of three dimensional images. These features are used to circumvent some of the limitations of conventional PIV. Some of these possibilities are demonstrated in this study by applying the technique to a high Reynolds number swirling flow using a lens-less off-axis orthogonal recording geometry.

Holography as a technique for the study of photopolymerization kinetics in dry polymeric films with a nonlinear response

A method is reported that makes use of holography to study the kinetics of the radical photopolymerization of acrylamide in a polyvinyl alcohol when the Kogelnik theory is applied. A mechanism of unimolecular termination by the radicals that initiate the polymerization reaction is postulated to calculate the quantum yield, the molar-extinction coefficient, the index of refraction, and the thickness of the film. The conversion percentage of monomers is obtained along with the ratio of rate constants of the mechanism of polymerization from the nonlinear fit of the transmittance curves, their angular response, and the temporal evolution of diffraction efficiency. Compared with previous holographic techniques, this method has the advantage of predicting these chemical parameters using all the data points of the temporal diffraction efficiency variation rather than being restricted to the linear zone of these curves. In this way the whole reaction process, not just the initial process, is taken into account.

A diffusion method for making silver bromide based holographic recording material

A simple diffusion method for the distribution of ultrafine silver bromide grains in pre-coated gelatin and customized polymeric films for holographic recording has been developed. The method involves two steps: immersion of the pre-formed film in a solution of a silver salt, followed by agitation of the film in a solution of a bromide salt containing sensitizing dye. Repetition of the operation on the same film with different sensitizing dyes in the bromide bath enables the production of film with a panchromatic response. Transmission electron microscopy reveals a grain structure very suitable for use in holography. A reflection hologram made by this method has a similar brightness under the same exposure and processing conditions to one made from a proprietary hologram recording material currently available.

Ensemble-Averaged Shack–Hartmann Wave-Front Sensing for Imaging Through Turbid Media

A technique is described for ensemble-averaging the light wave emerging from a turbid medium, enabling the recovery of optical information that is otherwise lost in a speckle pattern. The technique recovers both an amplitude and a phase function for a wave that has been corrupted by severe scattering, without the use of holography. With the phase estimated, an ensemble-averaged field is constructed that can be backprojected to form an image of the object obscured by the scattering medium. Experimental results suggest that the technique can resolve two object points whose signals are unresolved on the exit surface of a diffuser.

Wavelength dependence of wavefront correction using holography in a saturable absorber

We examine the use of holography to correct aberrated optical elements with different write and read beam wavelengths. The wavefront correction is obtained using nondegenerate four wave mixing in a thin saturable absorber. We show, for the first time, quantitative agreement between the corrected wavefront error and theory for a range of reading beam wavelengths that are up to a factor of two larger than the writing beam wavelength.

Endoholography, the use of holography in endoscwpy : Raviv, G. Dissertation Abstracts International, Vol. 47, No. 6, p. 2565 (Dec. 1986)

Endoholography, the use of holography in endoscwpy : Raviv, G. Dissertation Abstracts International, Vol. 47, No. 6, p. 2565 (Dec. 1986)

Morphology and crystallography of nano-particulates revealed by electron holography

Electron holography permits the precise determination of aspects of the morphology of nanometer-sized particulates, because the pure phase information in the image wave can be reconstructed and displayed. Profiles of intensity over the phase image are, in particularly advantageous cases, directly related to particle morphology, since the phase intensity for materials that are essentially kinematic scatterers and are of homogeneous composition is directly related to thickness. Holograms at high resolution can also be used for many other analyses of a material's structure; they provide, for example, a method for precise calibration of lattice spacings in nanometer-sized areas, that allows for the correlation of structure to processing parameters. Examples of the use of holography for studies of nanoparticles of oxides and model catalysts are given.

Holography as Large-Scale Event

The use of holography in non-gallery situations is not limited to art commissions. It is perhaps worth looking at two examples where the medium has been used for large-scale works. These pieces could not be considered primarily as art, but they have brought the medium of holography into direct contact with people who would not normally have access to it. Both works were produced by artists for large public festivals. The Canadian Pavilion at Expo '92 (Seville, Spain) included holographic water walls. Designed by American artist Melissa Crenshaw, these walls incorporated 3,000 square feet of specially produced holographic foil, which was laminated together and fixed onto glass. Water was allowed to fall over the glass walls and so manipulate the reflected light coming from the holographic surfaces. This was the first time such a large are.a of holograms had been installed and indicates the theatrical aspects of the medium. Unlike traditional theatrical lighting effects, this holographic wall manipulated color so that, depending how the wall was illuminated with white light and the location of the viewer, different colors would be produced. It is for this reason that the colors reflected from the wall and those reflected from the pool in front of the wall are different. What resulted was a constantly changing color environment that responded directly to the observer.

Hologrammetry: accurate dimensional measurement by holography

The use of holography for high-resolution inspection and measurement, i.e. hologrammetry, relies on the production of projected real images upon which optical sectioning can be performed. The concepts are outlined and their use in some unique industrial applications discussed.

Twenty forms of electron holography

Since the original proposal by Gabor for the use of holography as a means for the improvement of the resolution of electron microscopes, a number of schemes for electron holography have been proposed and several of these have been demonstrated experimentally. These include the in-line holography in transmission electron microscopy (TEM), i.e. the reconstruction from through-focus series of micrographs, and the off-axis holography in TEM using an electrostatic biprism. Gabor's scheme has been realized by use of a scanning transmission electron microscopy (STEM) instrument, on-line. By taking into account that for each TEM mode there is a STEM equivalent, and vice versa, and for each in-line mode there is an off-axis mode and dark-field as well as bright-field modes may be possible, a total of twenty possible modes of electron holography, distinctly different in either their theoretical basis or their experimental requirements, may be distinguished. Of these, seven have been demonstrated experimentally and two or three others have been analysed theoretically. Of the remainder, several offer prospects for future useful development. A simplified, one-dimensional, theoretical description of the holograms and possible methods for reconstruction is given to allow ready comparison of the various modes.

Photovoltaic spatial light modulator

A novel concept for implementing a high-resolution spatial light modulator using a thin slab of photorefractive LiNbO3 crystal is described. This method uses the photovoltaic effect to impress phase information onto the crystal without the use of holography where coherent reference beams are required. Experimental demonstration as well as an analysis of the operation and performance of the device are given.

Use of Holography in Vibration and Flutter Study of Fans

Use of Holography in Vibration and Flutter Study of Fans

Temporal reversal of picosecond optical pulses by holographic phase conjugation

We theoretically discuss the use of holography to achieve the phase conjugation of temporal signals. The reversal of a particular asymmetric pulse envelope is experimentally demonstrated. The holographic material is a photorefractive crystal used in a four-wave mixing configuration.

Use of Holography for Airborne Cloud Physics Measurements

Abstract The use of the holographic cloud particle imaging system developed by the Cloud Physics Branch of the Meteorological Office and carried on the C-130 Hercules aircraft of the Meteorological Research Flight (MRF) has hitherto been limited by the extremely labor intensive data extraction process. A new image reconstruction system has now been developed that enables numerous holograms from a single flight to be analyzed. A brief description of this system is given, and some of its uses and limitations are demonstrated by examples of both droplet and ice-crystal data. In each case, the holographic data are compared with those from what are now conventional cloud microphysical probes, principally the ASSP and 2-D Optical Array Probe. Results show that the holographic system can measure gross features of the droplet size spectrum in conditions when the ASSP data may be unreliable. Ice crystal measurements confirm the ability of the holographic technique to produce data down to sizes of about 60 μm, well...

Underwater hologrammetry: aberrations in the real image of an underwater object when replayed in air

The use of holography in the optical inspection and measurement of three-dimensional objects, now known as hologrammetry, places considerable emphasis on geometric precision and high resolution in the reconstructed real image. A discussion of the factors which dictate image fidelity in reconstruction must include an assessment of potential sources of optical aberration. In this paper the authors consider the aberrations introduced when the refractive index of the medium in which the subject is located differs from that in which the real image is replayed, addressing specifically their quantitative evaluation in relation to underwater hologrammetry.

High-power argon laser for use in holography

A cw stabilized ionic argon laser was constructed. The power of single-frequency radiation was 3 and 0.6W at wavelengths of 514 and 458 nm respectively. Active stabilization of the frequency ensured that the coherence length of the radiation was ~10 m.

Security applications of holography

The holograms now appearing on credit cards are but one aspect of the use of holography in security. New techniques to mass-produce holograms yet prevent their being copied offer a high degree of security at very low cost