Imaging the response of an organic nonlinear optical material

Shadowgraphs taken at four wavelengths indicate varying amounts of excited-state absorption in the focusing cone of a laser pulse within a sample of C60 in PMMA. The images provide information on the location and strength of excited-state absorption, and allow verification of excited-state lifetimes. Importantly, the transverse images provide direct experimental support for the role of both nonlinear refraction and nonlinear absorption in leading to a spatial redistribution of energy within the material. The technique, results and implications for modelling the laser–material interaction are briefly discussed.