Masters Thesis

Optical nonlinearities and ordering in aqueous and organic colloidal plasmonic materials

This thesis discusses four experiments on the ordering of gold nanorods. In the first experiment, a linearly polarized focused pump beam transmits through a solution of gold nanorods in water to create a soliton waveguide. A probe beam, linearly polarized at some angle with respect to the polarization of the pump beam, is then guided into the soliton channel. We then measure the output transmission as a function of the probe polarization to show the ordering of the nanorods in the soliton channel. Unfortunately, the results were not very reproducible. We discuss the possible reasons for experimental inconsistency and reproducibility. In the second experiment we use a set of parallel plates powered by a variable high voltage supply to create a controlled uniform electric field. These parallel plates are between a solution ofnanorods (aqueous or organic). We then shine white light and measure transmission and obtain the absorption spectrum of our ordered sample. We found the spectrum does not change with the voltage applied for our aqueous solution. But strong dependence of the spectrum on the voltage applied is observed for our organic (toluene) solution. In the third experiment, we use a similar setup as the first, but with a toluene solution of gold nanorods. Based on results from our second experiment we found noticeable ordering of nanorods in an organic solution compared to an aqueous nanorod solution. This motived us to explore the same experiment, but with organic solvent. In the fourth experiment, we use a pump beam to create soliton in our toluene solution of gold nanorods. We then add voltage to our parallel plates to see how an external electric field affects the non-linear action in our soliton. We also explored what happens when the pump beam power is too high and thermal effects break up the soliton. An external electric field is then added to investigate its effect on soliton formation. These experimental studies provide a step forward for optical manipulation of nanorods and for synthesizing plasmonic nanosuspensions with tunable optical nonlinearity.

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