Metal nanospheres under intense continuous wave illumination - a unique case of non-perturbative nonlinear nanophotonics
  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.
