Showing papers on "Diffraction efficiency published in 1970"

The use of photoresist as a holographic recording medium.

Abstract: A technique is described for recording holograms and forming diffraction gratings in Shipley AZ1350 photoresist using the 4579-A output from an argon laser. A pre-exposure technique is described that not only reduces exposure times but increases the signal-to-noise ratio of the image. It is also shown that the effects of the variable characteristic of the resist can be alleviated by monitoring diffraction efficiency during development.

Holographic Recording with Photopolymers

Abstract: Phase holograms have been recorded using several photopolymers. These photopolymer recording systems are self-developing and require only uv-light fixing. Sensitivities as high as 0.6 mJ/cm2 have been achieved with He–Ne–laser light. Reconstructions from 3000-line/mm gratings recorded on these materials have been achieved; however, the signal-to-noise ratio falls off above 1500 lines/mm. Microscopy has revealed that the hologram is recorded both on the surface and in the volume of the polymer, and that the surface modulation provides the dominant contribution to the diffraction efficiency for 25-μm-thick films.

Optical Frequency Shifting by Means of a Rotating Diffraction Grating

Abstract: The doppler frequency shift produced in the various diffraction orders of a rotating radial diffraction grating allows such a device to be used as an optical modulator. The theory and performance of such devices is presented.

Efficiency and Image Contrast of Dielectric Holograms

Abstract: The contrast and diffraction efficiency of a dielectric hologram made from a diffuse signal beam is calculated. Diffraction efficiency of 64% with acceptable image contrast is possible. Experimental results with holograms made by bleaching photographic emulsions are presented.

Thick absorption recording media in holography.

Abstract: The response of holograms recorded in thick absorption media is evaluated in terms of diffraction efficiency, angular orientation sensitivity, and wavelength sensitivity. Calculated results showing the relation between these measures of response and various hologram recording parameters are presented. These calculations are supported with experimental data obtained with thick photographic emulsions and various photochromic materials. In addition, experimental results are given which demonstrate the use of thick recording media in holographic data storage and multicolor wavefront reconstruction.

Optically Formed Dielectric Gratings in Thick Films of Arsenic–Sulfur Glass

Abstract: Although glass formation in the arsenic-sulfur system was reported as early as 1870 it is only since the early 1950's that any considerable attention has been given to such vitreous systems. Since then numerous papers have appeared dealing with arsenicsulfur glasses and with glasses derived from this system by addition and substitution of various elements. The field has been reviewed by Pearson. Most of the earlier studies have been concerned with the glassforming tendencies of various systems and with the physical, chemical, optical, electrical, and photoelectric properties of the resulting glasses. However, to the best of our knowledge no publications concerning the photochemical properties of these systems have appeared to date. I t is well known that binary arsenic-sulfur glasses and ternary arsenic-sulfur-bromine glasses with very high sulfur contents will devitrify spontaneously, precipitating elemental sulfur.Since all of these materials absorb energy very strongly in the visible region, it was of interest to ascertain whether light would induce the devitrification process in an otherwise stable glass. If such a change could be brought about, then the refractive index changes associated with the devitrification could be applied to hologram formation. Preliminary experiments demonstrated that the devitrification could be induced photolytically with 4880-A light and that holograms could be formed in these materials.

Techniques for producing low-noise, improved efficiency holograms.

Abstract: Photographic processing techniques for producing high efficiency, low noise phase holograms on silver halide emulsions have been investigated. Control of the emulsion and maintenance of the integrity of the holographic record throughout all processing were identified as prime requisites for high quality holographic reconstructions. Holograms have been obtained which yield approximately 30% diffraction efficiency and signal to scattered noise (S/N) in excess of 50:1 in the reconstruction of a diffuse wavefront. Holographic interferometry and ghost imaging with diffuse subjects has also been achieved with these techniques.

The Mechanism of Hologram Formation in Dichromated Gelatin

Abstract: Experiments have been performed which lead to the conclusion that dichromated gelatin holograms arise as a result of the formation of an air–gelatin interface, with the observed high diffraction efficiencies resulting from the air–gelatin refractive index differential of 0.52 found at the interface. It is postulated that rapid removal of water by isopropanol in the development process creates strains in the gelatin film which are relieved by splitting. The resultant cracks in the hologram manifest themselves in an obvious location, between the highly exposed planes of cross-linked gelatin. Photomicrographic evidence on Bragg-Lippmann and on plane gratings, liquid gate data, lack of thickness reciprocity for the gratings, and observations of grating thickness employing bandpass measurements comprise the bulk of the experimental work. From these data, a model is proposed that is consistent with all the experimental results for both Bragg-Lippmann and plane gratings.

Holographic Dielectric Grating: Theory and Practice

Abstract: Lossy dielectric gratings have been analyzed using a Raman-Nath formalism modified to incorporate losses. Four second-order coupled wave equations are retained for computation of the zero, first- and second-order diffracted beams for a multitude of practical cases. Significant differences are found in comparison with computations in which only two coupled waves are retained. The entire range of losses and thicknesses encountered for holograms in film emulsions has been studied using this unified approach. Graphs have been prepared to show the efficiency, i.e., power diffracted in the first-order relative to the total incident power, vs the index modulation for a wide range of thicknesses and losses. At a given thickness, optimum frequency requires a specific exposure. The efficiency for an optimum exposure is plotted vs the loss factor with thickness as a parameter. New experimental data are presented for bleached gratings in which several diffracted orders are measured and compared to our theory for a wide range of index modulation and loss factors.

Reflective-type narrow band filter

Abstract: A THICK TRANSMISSION HOLOGRAM IS BACKED BY REFLECTIVE MEANS TO PROVIDE A NARROW BAND FILTER OR WAVELENGTH SELECTOR. PARTICULARLY ADVANTAGEOUS ARE HOLOGRAMS WITH A DIFFRACTION EFFICIENCY OF APPROXIMATELY 50 PERCENT.

Diffraction gratings for spectroscopy

Abstract: The role of gratings in spectroscopy is reviewed together with their historical development. The ruling of master gratings, the engines required for that purpose and the subsequent replication, all representing the current state of the art, are described. A summary of grating physics is useful in deciding on specifications for a given application. The article includes a discussion on the blazing of gratings for maximum efficiency and the test procedures generally employed.

High Efficiencies, Low Noise, and Suppression of Photochromic Effects in Bleached Silver Halide Holography

Abstract: Interest in bleached photographic gratins and holograms arose as early as 1965.” Several theoretical investigations of photographically generated gratings showed that greatly improved efficiencies could be obtained by elimination of the absorption and reflection inherent in a silver imngc.a*Y This information stimu lated interest in improving diffraction efficiencies by bleaching processes, with reports indicating varying degrees of success. Nearly all investigators report the tendency of bleached silver emulsions to darken or discolor on further exposure to light.10 In addition it has proved difficult to attain high diffraction efficiencies with films.

Characteristics of dielectric holograms

Abstract: The diffraction efficiency and signal-to-noise ratio for two-dimensional and volume diffuse-signal-beam holograms are calculated and experimentally determined. Calculations are based on the statistical properties of the signal beam, and exact integrals rather than series approximations are used. High signal-to-noise ratio and high diffraction efficiency are possible, with the peak calculated diffraction efficiency being 22% for two-dimensional and 64% for volume holograms. The experimentally achieved efficiencies were 12% for two-dimensional and 36% for volume holograms.

On the Intensifying Property of a Pile-of-Gratings.

Abstract: The intensification property of a multilayer structure of aligned plane transmission diffraction gratings (pile-of-gratings) is described. A first-order analysis is given, based on addition of intensities, and the conditions under which intensification is possible are derived. Supporting experimental results are described.

Holographic Image Intensification by Superposition of Holograms

Abstract: The intensifying property of a multilayer structure comprising a pile of aligned plane diffraction gratings was recently described, and the applicability to image intensification from conventional holograms was suggested. The present note reports measurements of intensification optained from a pile of aligned thin conventional holograms of a diffusely scattering object, and a comparison with theory is made. Two sets of thin holograms were recorded, each set comprising a series of n identical holograms of the same back-lighted 5.0cm ground glass (i.e., a multi-point scattering object). The recordings were made on 1 cm portions of Agfa 10E70 film (0.14-mm-thick backing) in 6328-Å laser light using a conventional 2-beam holographic recording arrangement, in which the distance of the target and the reference point from the film were both about 32 cm, and the angle between the central ray from the target and the reference beam was about 30°. The two sets (A and B) differed in that set A (comprising seven recordings) was exposed to a higher density than set B (comprising twelve recordings); the ratio of reference to object beam irradiances (~1.2) was the same in both sets. For each set, direct measurement of image intensification in the reconstructed image was made, using a collimated 8-mm-diam laser beam, by measuring

Ray-diffraction method for handling complex incident fields

Abstract: A ray-diffraction method is described which is applicable to diffraction problems where the incident field on a diffracting edge cannot be represented as a single incident ray but exhibits a more complex form. The complex incident field may be represented by a combination of simple rays; the diffraction of each ray may then be treated individually. The total diffracted field is the sum of these diffraction components. The method is illustrated by applying it to the double knife-edge problem.

A new method for determining phase in optical diffraction patterns

Abstract: A method is described for the measurement of the relative phases of beams of laser light diffracted from a centrosymmetrical two-dimensional optical diffraction grating. The method relies upon the observation of interference effects when adjacent orders of diffraction yield overlapping beams of parallel light. The Fresnel diffraction pattern recorded is crossed by interference fringes whose positions and intensity distributions are governed by the phases and amplitudes of the diffracted beams. Computer simulation of the diffraction pattern indicates the possibility of phase recovery from patterns given by centrosymmetric diffraction gratings when two, three or four beams overlap, and suggests that the method may be extended to diffraction patterns from non-centrosymmetric gratings also. The potential of the method as an analogue for phase determination in crystallographic problems is indicated.