Femtosecond Z-scan and pump-probe measurements of silicon nanoclusters made by laser ablation and ion implantation

The recent measurement (ns excitation) of high optical nonlinearity in Si nanoclusters has generated interest in its potential use as an optical switch. The study of the nonlinear optical properties of Si nanoclusters (NCs) made by laser ablation and ion implantation techniques is motivated by the need for materials that exhibit large values of the real part of the third order nonlinear susceptibility (/spl chi//sup (3)//sub Re/). This is essential for light controlled phase or refractive index modulation at low power. The novelty of laser ablated Si NCs deposited on a quartz substrate is that the measured large nonlinearity results from the deposition of micron-sized droplets of Si composed of close-packed nanocrystallites of Si (3-50 nm). We believe that the nanocrystallites behave as a "coupled phased array of dipoles" exhibiting enhanced nonlinear optical properties due to quantum confinement. Based on the preliminary results, Si NCs samples are potential candidates for optical switching devices for Si based integrated optoelectronic systems which requires large /spl chi//sup (3)//sub Re/ and a relatively short lifetime. Additional Z-scan and pump-probe results are also presented.