Guiding and nonlinear coupling of light in plasmonic nanosuspensions.

We demonstrate two different types of coupled beam propagation dynamics in colloidal gold nanosuspensions. In the first case, 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. Although the IR beam does not experience nonlinear self-action effects, even at high power levels, needle-like deep penetration of both beams through otherwise highly dissipative suspensions is realized. In the second case, a master/slave-type nonlinear coupling is observed in gold nanoshell suspensions, in which the nanoparticles have opposite polarizabilities at the visible and IR wavelengths. In this latter regime, both beams experience a self-focusing nonlinearity that can be fine-tuned.