We have investigated the excitation of fluoresce molecules using nanoscale light confinement on the plasmonic nanostructures. We have fabricated gold nano-dimer arrays whose diameter and height were 100 and 20 nm respectively on 20-nm gold film with BK7 substrate with a period of 746 nm. We have calculated the field distribution by three dimensional finite-difference time-domain (FDTD) method and confirmed the field localization on the dimer’s gap whose size was 18 nm. The field confinement was induced by a light source at 671 nm and experimentally measured by near-field scanning optical microscopy (NSOM) under same incident condition given at FDTD calculation. The angle of surface plasmon resonance (SPR) was chosen to enable both fluorescence microscopy and SPR microscopy simultaneously. Given a resonance angle, a dimer could provide a subdiffraction-limited observation volume to study the dynamics of fluorescence molecules and a highly sensitive light scattering probe as a nanoantenna. By employing dual microscopic images, we could separate the fluorescence excitations within a subdiffracion-limited volume from those outside the volume. We calculated scattering intensities of fluorescence nanobeads on the dimer nanoantenna to assure the presence within an observation volume when they diffuse near the dimer nanoantenna with Brownian motion. We have applied the subdiffraction-limited volume to fluorescence correlation spectroscopy (FCS) to measure the dynamics of fluorescence molecules with high signal-to-noise ratio, with additional spatial analysis from SPR microscopy. The result of imaging FCS using gold nano-dimer with SPR microscopy shows novel applications for nanoscale sensing and imaging methods.
Heat induced by electromagnetic absorption affects optical properties and experimental conditions. For this reason, thermal effects in optics remain important. In this work, we investigate thermal properties of a wire-grid polarizer (WGP). A WGP is a well-known optical polarizing device and easy to combine with planar structures such as microfluidic channel and other optical components. We analyzed thermal characteristics of a WGP by considering the effects of various geometric parameters: wire-grid period, height, and fill factor. For far-field calculation of optical characteristics, rigorous-coupled wave analysis (RCWA) has been used with 40 spatial harmonics. Together, we solved wave-coupled heat transfer equation by 2D finite element method (FEM) for computing electromagnetic-thermal characteristics. 2D FEM calculation was verified with RCWA and 3D FEM. From the analysis, it was shown that a fill factor was the most dominant geometrical parameter for near-field thermal extinction. In addition, TM polarized light has higher local temperature T<sub>max</sub> = 354.5 K than that of TE polarized light T<sub>max</sub> = 331.7 K with an incident power at 0.1 mW/μm<sup>2</sup>. Polarization switching was found to induce thermal extinction of 4.78 dB with a temperature difference ▵T = 54.3 K in an identical WGP structure. Furthermore, the ratio of steady-state time was almost uniform within 15%, because the heat transfer mechanism is almost identical for TE and TM polarization. Time scale was on the order of μs. We expect this result to be useful for the integration of WGPs in polarization-sensitive thermal switching applications.