Localized Conical Edge Modes of Higher Orders in Photonic Liquid Crystals

Most studies of the localized edge (EM) and defect (DM) modes in cholesteric liquid crystals (CLC) are related to the localized modes in a collinear geometry, i.e., for the case of light propagation along the spiral axis. It is due to the fact that all photonic effects in CLC are most pronounced just for a collinear geometry, and also partially due to the fact that a simple exact analytic solution of the Maxwell equations is known for a collinear geometry, whereas for a non-collinear geometry, there is no exact analytic solution of the Maxwell equations and a theoretical description of the experimental data becomes more complicated. It is why in papers related to the localized modes in CLC for a non-collinear geometry and observing phenomena similar to the case of a collinear geometry, their interpretation is not so clear. Recently, an analytical theory of the conical modes (CEM) related to a first order of light diffraction was developed in the framework of the two-wave dynamic diffraction theory approximation ensuring the results accuracy of order of δ, the CLC dielectric anisotropy. The corresponding experimental results are reasonably well described by this theory, however, some numerical problems related to the CEM polarization properties remain. In the present paper, an analytical theory of a second order diffraction CEM is presented with results that are qualitatively similar to the results for a first order diffraction order CEM and have the accuracy of order of δ2, i.e., practically exact. In particular, second order diffraction CEM polarization properties are related to the linear σ and π polarizations. The known experimental results on the CEM are discussed and optimal conditions for the second order diffraction CEM observations are formulated

Molecular Effect in Semiconductors under Heavy-Ion Bombardment: Quantitative Approach Based on the Concept of Nonlinear Displacement Spikes

A model is developed which is able to describe depth profiles of the efficiency of the molecular effect in damage accumulation in semiconductors under heavy atomic and molecular ion bombardment. In the model, it is assumed that completely disordered zones form due to a catastrophic collapse of the crystalline lattice into an amorphous state when the disorder level within a collision cascade exceeds some critical value fc. Rather low values of fc are obtained for this spontaneous crystalline-amorphous transition within dense collision cascades produced in Si by heavy ions. Physical mechanisms responsible for such low values of fc are discussed