Title: Metal nanospheres under intense continuous wave illumination - a unique case of non-perturbative nonlinear nanophotonics,
Abstract: We show that the standard perturbative (i.e., cubic) description of the
thermal nonlinear response of small metal nanospheres to intense continuous
wave illumination is insufficient already beyond temperature rises of a few
tens of degrees. In some cases, a cubic-quintic nonlinear response is
sufficient to describe accurately the intensity dependence of the temperature,
permittivity and field, while in other cases, a full non-perturbative
description is required. We further analyze the relative importance of the
various contributions to the thermal nonlinearity, identify a qualitative
difference between Au and Ag, and show that the thermo-optical nonlinearity of
the host typically plays a minor role, but its thermal conductivity is
important.