Femtosecond dynamics of optical nonlinearities in nanocomposite films highly dispersed with semiconductor CdSe quantum dots

Photonic nanocomposite materials, consisting of one or several nanometer-size guest materials dispersed in a transparent host, have been paid much attention owing to their improved performance and new functionalities as well as to their flexibility in materials design [1]. They are generally fabricated by deposition/sputtering methods and take advantage of the local field effect and the nanostructuring properties to control the linear optical, laser gain and nonlinear optical properties [2]. Since 2002 we have developed a new class of inorganic-organic nanocomposite materials, the so-called photopolymerizable nanoparticle-polymer composites (NPCs) [3] in which multi-dimensional photonic lattice structures can be formed by holographic assembly of nanoparticles [4]. We have studied the nonlinear optical properties of NPCs dispersed with semiconductor CdSe quantum dots (QDs) acting as nonlinear nanoparticles [5]. We showed [6] that the dispersion of CdSe QDs as high as 6.8 vol.% to NPCs gave the cascaded fifth-order optical nonlinearity [7] as well as the saturable absorption. In this work we report on femtosecond pump-probe measurements of absorptive and refractive nonlinearities induced in NPC films highly dispersed with CdSe QDs by means of femtosecond pump-probe and transient grating methods.