  While plasmonic particles can provide optical resonances in a wide spectral
range from the lower visible up to the near-infrared, often symmetry effects
are utilized to obtain particular optical responses. By breaking certain
spatial symmetries, chiral structures arise and provide robust chiroptical
responses to these plasmonic resonances. Here, we observe strong chiroptical
responses in the linear and nonlinear optical regime for chiral L-handed
helicoid III nanoparticles and quantify them by means of an asymmetric factor,
the so-called g-factor. We calculate the linear-optical g-factors for two
distinct chiroptical resonances to -0.12 and -0.43 and the nonlinear optical
g-factors to -1.45 and -1.63. The results demonstrate that the chirality of the
helicoid-III nanoparticles is strongly enhanced in the nonlinear regime.
