Time scales and quantum-size effects in optical nonlinearities of semiconductor and metal

In the last few years, metal or semiconductor-doped glasses have been shown to possess attractive nonlinear optical properties. The Kerr nonlinearity of the embedded microcrystallites is enhanced by the local field effect or by the quantum size effect. Preparation, characterization and experimental techniques are described. The main results are then reviewed for both types of materials. For gold-doped glasses, the nonlinear mechanism is fully understood. Semiconductor-doped glasses fall info two categories: Larger particles for which the quantum size effect is weak and for which the nonlinear mechanism is mainly band filling and smaller particles exhibiting quantum confinement and behaving as saturable two-level systems; the importance of phonon broadening has been shown. In all semiconductor-doped glasses, photodarkening and Auger recombination strongly reduce the nonlinear response time.