In Situ Monitoring of the Shape Distribution of Metallic Colloids from Extinction Spectroscopy Measurements.

In this Letter, we propose a new, to the best of our knowledge, approach to determine the shape distribution of gold (Au) nanorods from real-time extinction spectroscopy measurements. This method is based on the linearization of the shape distribution effective medium theory (SDEMT). The aspect ratio distribution of Au colloids is obtained in a few tens of ms without any a priori information on the distribution. Both bimodal and monomodal shape distributions of nanoparticles can be extracted by analyzing their extinction spectra. The proposed method is applied to monitor the change in the nanoparticle shape during their exposure to ns-laser pulses.