Nonlinear optical properties of ultrathin metal layers

This thesis presents experimental and theoretical studies of nonlinear propagation of ultrashort long-range surface plasmon polaritons in gold strip waveguides. The strip plasmonic waveguides are fabricated in house, and contain a gold layer, adhesion layers, and silicon dioxide cladding. The optical characterization of the plasmonic waveguides is performed using femtosecond and picosecond optical pulses. Two nonlinear optical effects in the strip plasmonic waveguides are experimentally observed and reported. The first effect is the nonlinear power transmission of the plasmonic mode, and the second effect is the spectral broadening of the plasmonic mode. A consistent theoretical model of the nonlinear optical effects in the strip plasmonic waveguides based on the third-order nonlinear susceptibility of the constituent materials is developed and reported. It is shown that the effective third-order nonlinear susceptibility of the plasmonic mode in the gold strip waveguides significantly depends on the metal layer thickness and laser pulse duration. This dependence is explained in detail in terms of the free-electron temporal dynamics in gold. The third-order nonlinear susceptibility of the gold layer has the dominant contribution to the effective third-order nonlinear susceptibility of the longrange surface plasmon polariton mode in the strip plasmonic waveguides. The spectral broadening of the plasmonic mode in the waveguides is determined by
the real part of the third-order nonlinear susceptibility of the gold layer, and the nonlinear power transmission of the plasmonic mode is determined by the
imaginary part of the third-order nonlinear susceptibility of the gold layer. The experimental values of the third-order nonlinear susceptibility of gold for
ultrathin layers are presented. The pulse duration dependence of the third-order nonlinear susceptibility of gold is calculated in the broad range from tens of
femtoseconds to tens of picoseconds using the two-temperature model of the free-electron temporal dynamics of gold, and shows the saturation of the thirdorder
nonlinear susceptibility of gold for longer picoseconds pulses. The results are important for the development and applications of active plasmonic and
nanophotonic components.