Ultrafast nonlinear dynamics of surface plasmon polaritons in gold nanowires due to the intrinsic nonlinearity of metals

Nonlinear Dynamics of Ultrashort Long-Range Surface Plasmon Polariton Pulses in Gold Strip Waveguides

“…The obtained dependences confirm a significant increase in the third-order susceptibility for picosecond pulses over femtosecond ones due to better temporal overlap of longer pulses with the transient profile of the excited electron gas. 18,19 The data confirm that the ultrafast intrinsic "delayed" (i.e. noninstantaneous) temporal response function of free electrons in gold 18,19 is instrumental in modeling of the ultrashort LRSPP propagation with a nonlinear Schrödinger equation, with the continuous wave (cw) value of the third-order susceptibility being a single free parameter.…”

“…25 Meanwhile, the third-3 order susceptibility of gold, (3) Au  , in the IR wavelength range arises mainly from the intraband electron transitions and is much smaller than in the visible range. 18,19 Therefore, a conventional z-scan method may not be sensitive enough for nonlinear measurements in ultrathin gold layers.Nevertheless, the third-order nonlinearities of gold can be large enough to affect the signal propagation in a LRSPP waveguide due to the field localization near the metal interfaces and long propagation distance L SPP . 26,27 The third-order susceptibility of a gold film, which affects transmission (reflection) of light through (from) a film as well as propagation of plasmonic modes on the film interfaces is known to depend on both the pulse duration and thickness of the film.…”

“…[13][14][15] The nonlinear propagation of surface plasmon polaritons (SPPs) in plasmonic waveguides can be studied in terms of either the second-order nonlinearity, 16,17 or the third-order nonlinearity. 18,19 The latter is particularly important because it is present in all materials. In metals, it mainly arises due to hot-electron contributions from changes of the intrinsic electronic temperature after absorption of the incident light.…”

“…25 Meanwhile, the third-order susceptibility of gold, (3) Au  , in the IR wavelength range arises mainly from the intraband electron transitions and is much smaller than in the visible range. 18,19 Therefore, a conventional z-scan method may not be sensitive enough for nonlinear measurements in ultrathin gold layers.…”

“…20 The goal of this paper is to quantify such dependences in experiment and theory on nonlinear propagation of the LRSPP modes in Au strip waveguides. The nonlinear propagation is conditioned by the third-order susceptibility of gold, 18,19 and we use the nonlinear Schrödinger equation 28 for LRSPPs to study their propagation evolution. We measure the nonlinear absorption of the LRSPP mode in gold strip waveguides and present new experimental data on the imaginary part of the third-order susceptibility of gold for 200 fs pulses at a wavelength of 1030 nm.…”