Optical nonlinearities in plasmonic nanosuspensions

In this work we demonstrate coupled beam propagation dynamics in colloidal gold nanosuspensions. First we use an infrared (IR) probe beam (1064 nm) is guided by a low-power visible beam (532 nm) in a gold nanosphere or in nanorod suspensions due to the formation of a plasmonic resonant soliton. Next we report on the solitonmediated orientational ordering of gold nanorods in a colloidal plasmonic suspension. The orientation of the nanorods along the waveguide is regulated by the optical torque exerted by the linearly polarized soliton beam. By measuring the polarization transmission spectrum of a probe beam at a wavelength far from the plasmonic resonance, we observe orientation-enhanced birefringence along the soliton channel, suggesting a disorder-to-order transition of nanorods due to the action of the soliton beam.