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Direct optical coupling to the plasmon modes of a two-dimensional electron gas in a stratified semiconductor system requires an overlaid grating coupler. Plasmons can be excited with wave vectors equal to integer multiples of the grating wave vector, and the periodic screening by the grating splits these into two modes, symmetric and antisymmetric with respect to the grating profile. We present calculations of the dispersions and optical coupling strengths for several orders of both modes in a typical structure, and show that the splitting and coupling strengths of the higher order modes oscillate with varying grating mark fraction. These effects are discussed in terms of the oscillating field strengths and charge density profiles.

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Background: Energetic quarks in nuclear deep-inelastic scattering propagate through the nuclear medium. Processes that are believed to occur inside nuclei include quark energy loss through medium-stimulated gluon bremsstrahlung and intranuclear interactions of forming hadrons. More data are required to gain a more complete understanding of these effects. Purpose: To test the theoretical models of parton transport and hadron formation, we compared their predictions for the nuclear and kinematic dependence of pion production in nuclei. Methods: We have measured charged-pion production in semi-inclusive deep-inelastic scattering off D, C, Fe, and Pb using the CLAS detector and the CEBAF 5.014-GeV electron beam. We report results on the nuclear-todeuterium multiplicity ratio for π + and π − as a function of energy transfer, four-momentum transfer, and pion energy fraction or transverse momentum-the first three-dimensional study of its kind. Results: The π + multiplicity ratio is found to depend strongly on the pion fractional energy z and reaches minimum values of 0.67 ± 0.03, 0.43 ± 0.02, and 0.27 ± 0.01 for the C, Fe, and Pb targets, respectively. The z dependencies of the multiplicity ratios for π + and π − are equal within uncertainties for C and Fe targets but show differences at the level of 10% for the Pb-target data. The results are qualitatively described by the GIBUU transport model, as well as with a model based on hadron absorption, but are in tension with calculations based on nuclear fragmentation functions. Conclusions: These precise results will strongly constrain the kinematic and flavor dependence of nuclear effects in hadron production, probing an unexplored kinematic region. They will help to reveal how the nucleus reacts to a fast quark, thereby shedding light on its color structure and transport properties and on the mechanisms of the hadronization process.

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