This report outlines the possibilities to be found using one or more diffraction-limited high-quality light beams to activate a weakly absorbing gas in a regime where the diffraction spread can be controlled by converging optical devices to within a ratio ofJ2 of the minimum at the beam waist (corresponding lengths between converging elements are within twice the Rayleigh range). Our desigr.s use plane or cylindrical parallel mirrors down which a light beam is repeatedly reflected. In the first design variation,the beam is re-reflected up the parallel mirrors to the entrance aperture where it can be returned repeatedly for a number of multiply reflecting "travels" up and down the parallel mirror reaction chamber. In the second variation,the return of the beam after each multiply reflecting "travel" down the chamber is external to the chamber and is achieved by two mirror reflections. For diffraction control the return mirrors can be made converging.For multiple laser excitation, any of the external return mirrors can be replaced by a laser.The advantages of these designs are a high degree of uniformity of chamber illumination with a reasonably high number of passes. Drawbacks of the designs are the large space needed for beam return (many ten* of meters for some parameters) csnd (common to all high optical quality chambers) the figuring and reflectivity demands on the mirrors.
A review of lasers with potential photochemical applications in waste management indicates that dye lasers, as a class, can provide tunable laser output through the visible and near-uv regions of the spectrum of most interest to photochemistry. Many variables can affect the performance of a specific dye laser, and the interactions <>i these variables, at the current state ot the art, arc complex. The recent literature on dye-laser chara.-terisi ics has been reviewed and summarized, with emphasis on those parameters that most likely will affect the scaling of dye lasers in photochemical applications. Current costs are reviewed and correlated with output power. A new class of efficient uv lasers that appear to be scalable in both energy output and pulse rate, based on rare-gas halide excimers and similar molt-
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