Nonlinear polarization instability in cubic-quintic plasmonic nanocomposites.

We report a study of the nonlinear birefringence induced in a metal-dielectric nanocomposite due to the contributions of third- and fifth-order optical nonlinearities. A theoretical model describing the evolution of the light polarization state of a confined laser beam propagating through the nonlinear medium is developed with basis on a pair of coupled dissipative cubic-quintic nonlinear differential equations related to the two orthogonal polarizations of the optical field. As a proof-of-principle experiment we demonstrate the control of the light beam polarization in a silver-nanocolloid by changing the silver nanoparticles volume fraction, f, and the light intensity. A large nonlinear phase-shift (~20π) was observed using a 9 cm long capillary filled with silver nanoparticles suspended in carbon disulfide. Experiments using colloids with 1.0×10-5 ≤f≤4.5×10-5 and maximum light intensities of tens of MW/cm2 are performed. In addition, we demonstrate that the modulation instability is highly sensitive to the quintic nonlinearity contribution performed showing good agreement with the experimental results.