Femtosecond nearly resonant self-focusing in gold nanorod colloids

Abstract

We evaluate the threshold power for self-focusing in gold nanorod colloids of varying concentration by a power limiting method in the femtosecond filamentation regime. The pulses are tuned near the longitudinal plasmon peak of the nanorods, leading to saturation of linear absorption and reshaping of the particles. We evaluated the last two effects by optical transmission measurements and spectroscopic analysis and estimated that considerable particle deformation does not occur before the collapse of the beam. We performed numerical simulations based on the experimental results, and evaluated only a subtle, monotonically increasing enhancement of the nonlinear refractive index of the host material (water) as the nanoparticles concentration increases. The role of higher-order contributions is discussed. Our work provides an alternative characterization approach of ultrafast nonlinearities in absorbing media. It further emphasizes that self-focusing of intense femtosecond pulses in gold nanocomposites is hampered by the ultrafast modulation of the susceptibility of the metal.

Influence of photothermal and plasma-mediated nano-processes on fluence thresholds for ultrafast laser-induced cavitation around gold nanoparticles

“…The double pulse experiments demonstrated an excess required fluence for cavitation, which can be attributed to either electronic losses or transient absorption effects. 36 However, as shown by pump–probe spectroscopy, 13,37 the absorption of particles is expected to transiently (marginally) increase at the pump wavelength (800 nm), which contradicts the observation for excess fluence requirement. Thus, the effect is most likely associated with electronic losses.…”

Nonlinear Propagation of Laser Light in Plasmonic Nanocomposites

“…The result has been understood in the context of a synergistic effect of the ultrafast saturable permittivity (thus saturable local‐field enhancement) and particle deformation near the threshold of filamentation. [ 176 ]…”

“…The solid and dotted curves correspond to numerical simulations by solution of a nonlinear propagation equation of Schrödinger type, which accounts for saturation of absorption. Adapted under terms of the CC-BY license [176]. Copyright 2021, The Optical Society.…”