Nanostructured materials and composites for optical power limiting

This paper discusses methods used in our laboratory to design and prepare nanostructured materials and nanocomposites for optical power limiting. At the molecular level, we are studying structure-property relationship in a group of sequentially made and systematically derivatized structures with an objective to enhance the two-photon absorption cross-section. At the bulk level, nanoscale synthesis and processing in confined geometries such as those provided by the cavities in reverse micelles and pores in sol-gel glasses are utilized to prepare nanoparticles and nanocomposites. By these approaches we are able to combine a number of processes such as multiphoton absorption, reverse saturable absorption, photochromism, and nonlinear scattering, each of which can produce power limiting action under different conditions. Femtosecond time-resolved, pump- probe transient absorption experiment has been used to understand the excited state dynamics, particularly excited state absorption and its importance in power limiting action.