Ultrafast nonlinear dynamics of thin gold films due to an intrinsic delayed nonlinearity

Abstract

Abstract. Using long-range surface plasmon polaritons light can propagate in metal nano-scale waveguides for ultracompact opto-electronic devices. Gold is an important material for plasmonic waveguides, but although its linear optical properties are fairly well understood, the nonlinear response is still under investigation. We consider propagation of pulses in ultrathin gold strip waveguides, modeled by the nonlinear Schrödinger equation. The nonlinear response of gold is accounted for by the two-temperature model, revealing it as a delayed nonlinearity intrinsic in gold. The consequence is that the measured nonlinearities are strongly dependent on pulse duration. This issue has so far only been addressed phenomenologically, but we provide an accurate estimate of the quantitative connection as well as a phenomenological theory to understand the enhanced nonlinear response as the gold thickness is reduced. In comparison with the previous works, the analytical model for the power-loss equation has been improved, and can be applied now to cases with a high laser peak power. We show new fits to experimental data from literature and provide updated values for the real and imaginary part of the nonlinear susceptibility of gold for various pulse durations and gold layer thicknesses. Our simulations show that the nonlinear loss is inhibiting efficient nonlinear interaction with low-power laser pulses. We therefore propose to design waveguides suitable for the mid-IR, where the ponderomotive instantaneous nonlinearity can dominate over the delayed hot-electron nonlinearity and provide a suitable plasmonics platform for efficient ultrafast nonlinear optics.

Coupling light and sound: giant nonlinearities from oscillating bubbles and droplets

“…Here, one may employ materials with high optical nonlinearities such as chalcogenide glasses [36,37], silicon [38,39], and AlGaAs [40,41]. Alternatively, one can exploit optical nonlinearities of noble metals such as gold [42,43,44]. However, factors such as immature fabrication technology for chalcogenide glass, high linear and nonlinear losses for semiconductors, and high losses in metal structures due to the excitation of plasmon resonances [45] motivate the search for alternative materials such as silica-based glasses [46] and indium tin oxide [47].…”

Heat-induced soliton self-frequency redshift in the ultrafast nonlinear dynamics of active plasmonic waveguides

“…In practice, the gold nonlinear susceptibility at optical and near-infrared frequencies is determined by the interband transitions around the X, L points in the first Brillouin zone and thermo-modulational effects arise from Fermi smearing of the electronic energy distribution in the conduction band. Theoretical and experimental investigations on the temporal dynamics of such a process indicate that the nonlinear response of gold is characterised by a delayed mechanism resulting from the different time scales of electron-electron and electron-phonon scattering [23][24][25]. Such a delayed response is responsible for a strong deceleration of femtosecond optical pulses accompanied by redshift in the frequency domain [12].…”