Photodarkening and partial photobleaching: application to dichromated gelatin.

Photodarkening or partial photobleaching of photochromic solid media is described by means of an approximated analytical equation. The equation shows that the effective rate of the photochemical reaction is proportional to the square root of the final transmittance of the illuminated layer. The model is applied to describe the photodarkening of dichromated gelatin at 488 nm.

Photochromic behavior of spiropyran in polymer matrices.

The photoexcitation, relaxation, and optical erasure regimes of spiropyran- (SP-) doped polymer films were studied. Cellulose acetate, poly(vinyl acetate), and poly(methyl methacrylate) (PMMA) were used as host polymer matrices. We studied the character of the photoreaction for both coloring and bleaching processes. Reversible holographic recording in SP-PMMA films and the origin of the photochemical fatigue was studied upon repeated UV-visible irradiation cycles.

Degenerate four-wave mixing geometry in thin-film waveguides for nonlinear material characterization.

We demonstrate experimentally a new degenerate four-wave mixing (DFWM) geometry in waveguides that permits the simultaneous determination of the nonlinear refractive index, the absorption, and the response time of the thin-film materials. The geometry consists of two guided pumps in a planar waveguide with an unguided probe. We achieve nonlinear characterization by measuring only the DFWM signal and the guided pump power at the waveguide output. The technique has been tested on a polymeric film (di-alkylaminonitro- stilbene).

Factors related to outcome following a work hardening program.

The purpose of this study was to determine factors related to a return to work following the completion of a work hardening program. Data from the Workers' Compensation Board of Alberta Millard Rehabilitation Centre for 1527 discharges, collected over 22 months, were examined retrospectively. Factors related to return to work were compared bivariately using logistic regression procedures. A multiple logistic regression model for return to work was also determined. The principle predictor of return to work was job-attached status to the pre-injury employer. Other factors related to return to work were education, primary diagnosis, injury to admission time, job attachment to the pre-accident employer, employer's annual payroll, and vocational direction. Due to the strength of the association between job-attached status to the pre-injury employer and a return to work, it was concluded that attempts to maintain this relationship should be a priority for rehabilitation providers and insurance carriers.

Computer-generated holograms on a metal ion-doped polymer system: contact copying.

Dichromated poly(acrylic acid) films with dimethyl formamide have been used as a real-time recording medium for volume transmission holograms. In this study a simple computer-generated holographic grating with a sinusoidal amplitude profile is copied onto this recording material by the contact-copying technique. The experimental setup for the contact copying of a computer-generated hologram (CGH) is explained, and the phase modulation is observed for a different exposure time. Theoretical and experimental diffraction efficiency values for the CGH copy are also evaluated. Photographs of the original and copy of the CGH on the photopolymer film are presented.

Modified holographic recording setup for photopolymerizable/flexible recording materials.

An improvement in the conventional holographic recording setup has been done for liquid (photopolymerizable) or flexible recording materials. The new vertical recording setup that comprises a horizontal substrate holder permits holographic recording on such materials without positioning them between two substrates, as has been done until now. This setup can be conveniently used for the fabrication of transmission, reflection, Fourier transform, and computer-generated holograms with few simple modifications as indicated.

Multiple beam generation using a stratified volume holographic grating.

The parameters of several stratified volume holographic gratings are optimized in order to obtain high diffraction efficiency beam spliters. Two-, three-, five-, seven-, and nine-beam fan-outs are theoretically studied and compared with what has been achieved by other means. With a simple optical setup, a fan-out element that generates seven beams of equal intensity is experimentally realized and a comparison with theory is made.

Real time bleaching of methylene blue or thionine sensitized gelatin.

The kinetics of bleaching of methylene blue or thionine sensitized gelatin plates are investigated with a singlebeam exposure experiment. It is found that thionine bleaching can be modeled by a first-order theory; whereas, a higher-order theory is found necessary to explain methylene blue bleaching.

Real time hologram reinforcement demonstrated by thionine/PVA photoreducible thin layers.

Thionine dye dissolved in polyvinylalcohol matrix is a well-known photoreducible system that shows photochromism. Experiments on a real time hologram recording process performed by this system are presented here. During the reading process, a grating reinforcement was observed, and this phenomenon is qualitatively discussed.

Methylene blue sensitized gelatin: evidence of photodemethylation.

The dependence of diffraction efficiency of methylene blue sensitized gelatin gratings vs dye concentration is explained in terms of the aggregations tate of the dye.

Influence of the substrate temperature on the holographic properties of Se and SeGe thin films.

The effects of the substrate temperature (T(s)) on the optical constants of as-deposited Se and SeGe thin films and on the holographic recording properties of these films were investigated. The substrate temperature held between 35 degrees C and 50 degrees C during thin film deposition was identified as an appropriate means to improve the optical recording properties of these films.

Processing of holograms recorded in methylene blue sensitized gelatin.

The properties of gelatin films sensitized only with methylene blue are discussed, and a modified development process which gives higher diffraction efficiency for phase holograms recorded with a He-Ne laser is presented. The behavior of transmission and reflection gratings recorded in that medium is also studied.

Modulation transfer function measurements for thin layers of azo dyes in PVA matrix used as an optical recording material.

Diffraction efficiencies and characteristic erasure times were measured for two recording materials suitable for real-time holography and four-wave mixing. A study of real-time transmission volume grating formation was done in conjunction with polarization states of the writing beams for 30-microm thick layers. Modulation transfer function curves presented were obtained using a versatile device for which the spatial frequency domain was 500-4000 cycles/mm.

Degenerate four-wave mixing in organic azo dyes chrysoidin and benzopurpurin 4B.

Phase-conjugate reflectivity obtained by degenerate four-wave mixing are measured in different azo dye solutions. A reflectivity up to 80% was achieved. Values of the nonlinear susceptibility chi((3)) are calculated, and its origin is discussed.

Hydrogen-implanted SeGe alloys as optical recording media.

Thin films of Se(x)Ge(1-x) have been used as optical recording media for x values of 0.33, 0.5, and 0.67. An investigation of the effect of hydrogen implantation into thin films of this material on optical recording parameters has been performed in the range from 10(14) to 10(16) ions/cm(2). Parameters such as writing energy and contrast ratio were mainly studied. Pulsed holography was also achieved.

Methylene blue sensitized gelatin as a photosensitive medium for conventional and polarizing holography.

The properties of thin gelatin films sensitized with a dye (methylene blue) when used as a holographic material are discussed. On illumination the excited dye molecule changes its structure giving a colorless molecule. The higher rate of bleaching and therefore the higher diffraction efficiency of the developed phase gratings are obtained in an oxygen-free atmosphere. Furthermore, the light absorption probability of the dye molecules depends on its position with respect to the electric vector of the light, with the result that the exposed part of the dye becomes dichroic when illuminated with linearly polarized light. This result allows the use of this material for polarizing holography.

Real-time hologram recording in SeGe films.

Hologram characteristics of Se(1-x)Ge(x) (x = 0, 3,5,8, 12 wt.%) films were determined in real-time configuration. Parameters such as film thickness, composition, and exposure power influencing the diffraction efficiency were also studied. The maximum value of the diffraction efficiency achieved was 3.2% with 91.0-mW/cm(2) power in films alloyed with 3% Ge. Microstructural changes before and after the exposure were determined using transmission electron microscopy.