Sylvia H. Stevenson

3-Methyl-4-methoxy-4′-nitrostilbene (MMONS): Crystal structure of a highly efficient material for second-harmonic generation ☆

Abstract We report the preparation and crystal structure of 3-methyl-4-methoxy-4′-nitrostilbene (MMONS). MMONS generates second-harmonic radiation with a powder efficiency 1250 times that of urea; this is the largest measured powder SHG efficiency reported to date. MMONS crystallizes in the space group Aba2; the packing is made up of stacks of four molecules in a donor-acceptor-acceptor-donor configuration with π-π interactions resulting in short intermolecular distances between these four phenyl rings of 3.36–3.50 A. We suggest that charge-transfer excitons within the crystal may account for the large observed nonlinearity.

New organic non-linear optical materials of stilbene and diphenylacetylene derivatives☆

Abstract We report a series of new optically non-linear organic molecules of stilbene and diphenylacetylene derivatives. We have measured their powder second-harmonic generation efficiency and, in certain cases, the second-order molecular polarizability, β. This series of molecules is characterized by: (1) very large non-linearity, (2) high probability of forming non-centrosymmetric crystal structures, and (3) polymorphism. A number of relatively weaker donors: methoxy, bromo, and iodo, have been identified as effective moieties to enhance the intrinsic molecular non-linearity. Using weak donors to prepare highly non-linear optical materials provides advantages of having better optical transparency and high probability of forming acentric structures.

Color holography using DuPont holographic recording films

DuPont has developed holographic photopolymer films capable of producing high diffraction efficiency in full-color volume holograms and holographic optical elements. The properties of these films allows for a greater range of applications than has been considered feasible for color holograms. The recording mechanism and methods for holographic color recording in these materials is considered. Methods for full-color mastering and copying to achieve optimal performance in three-color recording are discussed. Examples of full-color holograms are presented.

Photopolymer materials for color holography

DuPont has developed full color holographic photopolymer films with high sensitivity across the visible spectrum, which can be used to produce high performance full-color volume holograms and holographic optical elements. In addition, three color mastering films have been developed to produce high quality full color master holograms. Methods and results of holographic color recording and mastering in these materials are discussed. Examples of full- color display holograms and simple holographic optical elements are presented.

Improved process of reflection holography replication and heat processing

A method is presented for rapid processing of high volumes of reflection holograms recorded in rolls of DuPont OmniDexTM photopolymer films. This process includes high-volume continuous holographic replication, color tuning lamination and scroll over heating. Performance data for commercial OmniDex films processed with this method is presented. Performance and yield data from trial production runs demonstrate process capacity of at least 2500 square feet per day.

DuPont multicolor holographic recording films

DuPont has developed photopolymer materials for recording volume phase holograms. These unique materials record the complete wavefront of light from an object as a periodic refractive index modulation throughout the thickness of the film. Materials have been designed and developed for reflection and transmission holograms for a variety of applications. Recently, new materials with panchromatic sensitivity, designed specifically for color display holography, have been developed. This paper presents DuPonts new color material designed for reflection display holography. An overview of the recording mechanism, holographic performance, and process of use is given. Experimental color balancing results are discussed, and performance is compared to that of a film with different color balancing characteristics.

Advances in photopolymer films for display holography

Improved performance holographic photopolymer films have been developed and are available for use in recording volume reflection holograms for display holography. This paper discusses the properties of images recorded in DuPont OmniDexR 706 holographic recording film and images shifted in color using OmniDexR GA2-RED color tuning film and the OmniDex dry color tuning process. Process of use and process latitude for both kinds of images are described. Several process variation methods for controlling the appearance of the final image are discussed.

Method for characterization of film thickness and refractive index in volume holographic materials

Independent characterization of changes in film thickness and refractive index is necessary for accurate prediction of the Bragg playback conditions of volume holograms after processing. We have developed a method which uses weak holographic mirrors to characterize processing- induced swelling or shrinkage and index change in volume holographic films, and have applied this method to DuPont OmniDexTM holographic recording films. Results of these measurements are presented.

Environmental performance of photopolymer holographic optical elements

A variety of environmental exposure tests were conducted on holographic optical elements. Previous reports from our lab have largely been confined to studies on simple mirror holograms in unconverted format. This study was expanded to include slant-fringe diffuse reflectors as well as normal- incidence simple mirrors converted into commercially practical formats with adhesives and different types of support substrates. Holograms were characterized using reflectance as well as transmission spectroscopy. Films were subjected to 30 cycles of 80 degree(s)C to -30 degree(s)C air-to- air temperature cycling, 14 day 70 degree(s)C/95% RH hold, 14 day 100 degree(s)C dry heat hold, 540 hour continuous ultraviolet exposure, and 14 day cycled fluorescent roomlight exposure. Playback wavelength and diffraction efficiency was stable under all conditions. As reported earlier, exposure to intense ultraviolet light increases yellowness of the photopolymer holograms, but this can be prevented by laminating a UV-absorbing layer atop the film.

Display applications for holographic optical elements

In the last several years, holographic elements have been introduced into a wide array of display applications. Holographic Reflectors are incorporated with liquid crystal displays to shift optimum viewing angle away form specular glare and raise brightness by concentrating light at a convenient viewing angle. Reflectors can be produced in blue, green, gold, red, or white colors. Denso GlassVision projection screens incorporate transmission holograms to efficiently direct projected light to the viewer in a screen that reverts to clear glass When the projection image is turned off. JVC has introduce da large-screen HDTV that uses a holographic color filter to separate blue, green, and red light from the illumination beam, and direct the sorted colors to the appropriate color pixel, raising brightness with a passive component. Most recently, HOE prototypes have been produced to improve the efficiency of portable liquid crystal color display. Front diffuser are affixed to the face of reflective color LCDs and direct output light from the LCD to the viewer at a convenient viewing angle in a concentrated view cone. Reflective Colors Filters are pixelated diffuse reflectors internal to the LCD structure and aligned to the LCD matrix. These reflective filters provide higher brightness, larger color gamut, and better color saturation including a holographic grating are under development to provide wider view angle in direct-view LCDs.