Optical Limiting with Nanocrystalline Materials

"Broadband visible optical limiting filters will be an essential element for soldier protection in the future battlefield environment. New materials are required that provide protection for the eye for pulses >0.5 mJ, so that the threshold at which theybecome absorbing or scattering through damage is <0.5 J/cm2 at an intermediate focal plane. We propose to use suspensions of unaggregated absorbing nanoparticles for optical limiting. Such nanoparticles can exhibit optical limiting by several mechanisims,including charge trapping inducing plasmon and donor/acceptor absorption, and local heating leading to formation of light scattering plasmas, shock waves and bubbles. In Phase I, using new synthetic methods for semiconductor nanoparticles ("quantum dots"),we will prepare broad band absorbing monodisperse (1-10 nm diameter) particles of several candidate semiconductors and evaluate their optical limiting behavior in comparison to polydisperse C suspensions. These will provide highly reproducible filters witha low damage threshold due to their small size and also due to charge trapping effects. Phase Ia and II will entail additions of donor/acceptor nanoparticle surface complexing moieties to enhance the charge separation mechanism, and the development ofsolid matrices for creating stable dispersions and high optical quality filter elements. The new filters have government markets for eye protection of military personnel and for sensor