Polarization-resolved two-photon luminescence microscopy of V-groove arrays

Using two-photon luminescence (TPL) microscopy and local reflection spectroscopy we investigate electromagnetic field enhancement effects from a µm-sized composition of 450-nm-deep V-grooves milled by focused ion beam in a thick gold film and assembled to feature, within the same structure, individual V-grooves as well as one- and two-dimensional 300-nm-period arrays of, respectively, parallel and crossed V-grooves. We analyze TPL signal levels obtained at different spatial locations and with different combinations of excitation and detection polarizations, discovering that the TPL emitted from the V-grooves is polarized in the direction perpendicular to that of the V-grooves. This feature implies that the TPL occurs solely in the form of (p-polarized) surface plasmon modes and originates therefore from the very bottom of V-grooves, where no photonic modes exist. Implications of the results obtained to evaluation of local field enhancements using TPL microscopy, especially when investigating extended structures exhibiting different radiation channels, are discussed.