Introduction.
Nonlinear and guided wave optics and photorefractive effects are matured sciences, and are playing an ever increasing role in various fundamental and applied research fields. In the spirit of the focused issues, we have deliberately narrowed our attention to novel, unusual but no less interesting areas of pursuits. Although this focus issue contains only six papers, the readers will notice that it covers quite a range of material systems and optical processes. The so-called guiding core materials include semiconductors, crystals, liquid crystals and liquids; understandably, gaseous cores are not included at this point in time. The nonlinear optical effects arise from quantum processes in semiconductors, electron-holes in photorefractive crystals and multi-photon and excited electronic-state absorptions in molecules, as well as from truly classical processes such as elastic torques and hydrodynamics in liquid crystals, and thermal and density fluctuations in liquids.
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