Most of the paper authors have illuminated nano-structures with pulsed laser (wavelength:~nm range and pulse duration: ~ps range) to observe the scattering or extinction cross-section.
Sorry sir, let me rephrase - in most of the paper I have read till now, pulsed laser have been used to illuminate the nano-structures.
Observed cross-sections are in few nm^2 range. As for example, in [1] 70 nm diameter plasmonic nanodisc is used as an antenna and in [2] connected pentamer (1st generation) of length : 165 nm and width : 90 nm is used as a nanoantenna.
[1] Schumacher T et al., Nanoantenna-enhanced ultrafast non-linear spectroscopy of a single gold nanoparticle, Nature communications, 2011.
[2] Guo ke et al., Dendritic optical antennas: scattering properties and fluorescence enhancement, Nature scientific reports, 2017.