Abstract
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.
Highlights
Electromagnetic interactions in nanostructured materials and, especially, in metal nanostructures give rise to various fascinating optical phenomena
In this work, using polarization-resolved two-photon luminescence (TPL) microscopy in combination with spatially-resolved linear reflection spectroscopy, we investigate a 7×7-μm2-sized structure composed of 450-nm-deep V-grooves milled by focused ion beam (FIB) in a thick gold film and assembled to feature, within the same configuration, individual V-grooves as well as oneand two-dimensional 300-nm-period arrays of parallel and crossed V-grooves (Fig. 1)
Summarizing, using polarization-resolved TPL microscopy and spatially-resolved reflection spectroscopy we have investigated electromagnetic field enhancement (FE) 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
Summary
Electromagnetic interactions in nanostructured materials and, especially, in metal nanostructures give rise to various fascinating optical phenomena. Realization of field enhancement (FE) that enforces surface enhanced Raman scattering (SERS) is extremely important for highly sensitive detection of low molecular concentrations [2], reaching the limit of single molecule detection [3] In this perspective, metal nanostructures supporting surface plasmon (SP) resonances have been intensively investigated with respect to achieving strong FE effects [1]. Note again that for the previously investigated similar structures, such as tapered gaps [15, 16] and periodic slits [28, 29], we have used the unpolarized detection (i.e., without an analyzer in front of a detector) of generated TPL in order to maximize the recorded signal-tonoise ratio This is a reasonable procedure since luminescence is an incoherent process without preferred polarization, and detecting only a certain polarization would normally not add additional information except for merely decreasing overall signal levels. We observed the effect of individual, 1D and 2D V-groove configurations in the same structure and with fixed parameters of depth and spacing between the V-grooves thereby rendering TPL measurements of different areas in the same scan to be directly comparable
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