Irradiation of solutions of all-trans octatetraene in n-octane and cyclohexane at temperatures below 10 K efficiently produces a photoproduct whose fluorescence and absorption spectra are shifted ∼1200 cm−1 to lower energy than the corresponding features in the all-trans precursor. High resolution excitation and fluorescence spectra and fluorescence lifetimes for this product have been determined. These data establish that the photoproduct is a noncentrosymmetric octatetraene isomer. The spectroscopic properties and thermal lability of this isomer are consistently interpreted if it is assumed that the photoproduct is generated from all-trans octatetraene by isomerization about one of the single bonds.

Quantitative interpretation of the absorption and emission spectra of 1,8diphenyl1,3,5,7octatetraene J. Chem. Phys. 79, 2495 (1983; 10.1063/1.446091The fluorescence and the absorption spectra of 1,8diphenyl1,3,5,7octatetraene. The origin of the transition moments and the interpretation of anomalous intensity distribution J. Chem. Phys. 76, 5672 (1982); 10.1063/1.442988Experimental confirmation of the dipole forbidden character of the lowest excited singlet state in 1,3,5,7 octatetraene J.The decay kinetics of the 2 lAg state of the linear polyene l,3,5,7·octatetraene in hydrocarbon solutions have been measured by nanosecond and picosecond techniques from 10 to 320 K. The observed decrease in emission lifetime with increasing temperature is well described in terms of a temperature activated intramolecular radiationless decay process proceeding over a ~4 kcal Arrhenius barrier. This barrier is not significantly affected by intermolecular interactions such as sample viscosity or phase and may be related to rotation about essential single bonds in the excited state.

At temperatures below 10 K photolysis of solutions of all-trans octatetraene in n-octane efficiently produce a photoproduct which has been identified as an s-cis isomer. This paper reports quantitative measurements of the relative concentrations of this photoproduct and the all-trans precursor as a function of irradiation and temperature. These data establish that the primary photochemical channel open to all-trans octetraene under these conditions leads to the production of the s-cis isomer which, at temperatures above 50 K, quantitatively reverts to the all-trans form. This thermal reversion is well described as an activated first order process proceeding over a barrier of 4.0±0.2 kcal/mol. A model for computing isomerization rate constants from a simple one-dimensional potential also quantitatively fits the data. In this model the barrier height for s-cis to s-trans conversion is 3.16 kcal/mol, the enthalpy of the s-cis species is 2.88 kcal/mol above that of the all-trans and the internal rotor is a terminal ethylene group.

One approach to flat sensor design is to use a lenslet array to form multiple subimages of a scene and then combine the subimages to recover a fully sampled image by using a superresolution algorithm. Previously, superresolution image assembly has been based on information derived from the observed scene. For lenslet arrays, we propose a new scene-independent approach based only on known imager properties in which relative subimage shifts are accurately estimated with a calibration procedure using point source imaging. Thus, the relative resolution enhancement provided by the scene-independent superresolution algorithm is impervious to changes in subimage content, contrast, sharpness, and noise.

Low-cost compact sensors for ultrasmall systems are a pressing need in many new applications. One potential solution is a shallow aspect ratio system using a lenslet array to form multiple undersampled subimages of a scene on a single focal plane array, where processing techniques then produce an upsampled restored image. We have investigated the optimization and theoretical limits of the performance of such arrays. We have built a hardware simulator and developed algorithms to process imagery similar to that of a full lenslet imaging sensor, which allowed us to quickly test optical components, algorithms, and complete system designs for future lenslet imaging systems.