Photopolymers formed from the family of thiol-X "click" reactions notably form sulfur-containing thioether linkages. While sulfur-containing materials are conventionally expected to result in high refractive index (n D /20 °C > 1.6) materials, this expectation is rarely realized with thiol-X photopolymers, because of the lack of monomers with sufficiently high refractive indices. Here, an efficient, modular synthetic strategy to obtain high refractive index thiol-X monomers is presented. The efficacy of the overall approach is demonstrated using only commercially available starting compounds to yield low viscosity (<500 cP) liquid multifunctional thiol and diallyl ether monomers with high refractive indices (n D /20 °C > 1.64). These synthesized monomers underwent rapid thiol-ene photopolymerizations to high conversions, achieving refractive index values (n D /20 °C) up to 1.669 in uniform crosslinked networks exhibiting typical narrow and well-defined loss tangent (tan δ) peaks. The convenience of the low-viscosity, high optical quality thiol-ene resins was demonstrated in the fabrication of two functional optical components. First, a plano-convex lens was aspherized using an overmolding procedure. Second, a two-dimensional grating was fabricated using a two-stage material and a photomask exposure.
Effect of cyclotron resonance on the microwave detection properties of a glow discharge plasma Am.centimeters even at frequencies as high as 100 GHz. In practice, the attenuation of such waves in samples of ordinary dimensions is probably governed by surface irregularities. It is only when the lOOO-GHz region is reached that the anharmonic processes discussed here would form an important attenuation mechanism at low temperatures (in that case well below SOCK).At higher temperatures the anharmonic processes will be more important. In quartz (e = 600 o K, M v 2 / K = SOOOOoK, vI=6XlO 5 cm/sec) and at 114 GHz one would expect a to be about 1XlO-3 cm-I at T=O and about 1 X 10-1 at lOoK. Ilukor and Jacobsen 2 found an anharmonic attenuation about a factor ten larger at that temperature and frequency. The discrepancy may well be due to collinear prOCesses of the type L~ L+ L, which we have not considered here, but which playa large role at lower frequencies. 6 • 7 These processes can be important when KT> nw, though they should lead to an attenuation proportional to the first power of frequency, and the extra attenuation found by Ilukor and Jacobson is considerably higher than would be indicated by an extrapolation from the results of Thaxter and Tannenwald l at 70 GHz. Clearly one needs not only a better theory, particularly calculations for the awkward region nw~KT, but also more experimental data.Acceleration of a microwave-energized plasma by expansion in a diverging magnetic field is studied. Results of a theoretical collisionless particle analysis are reviewed. An experimental accelerator is described and its pertinent conditions are considered. Measurements of plasma beam shape and potential are compared with the theoretical predictions. The conclusions are that, while some experimental characteristics (beam shape and potential profile) agree with theory, col)isions in the experimental device prevent it from attaining operating conditions predicted by collisionless theory.
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