| The goal of near-field plasmonic microscopy is to develop an imaging tool with nanometer scale spatial resolution that can visualize the targets at the molecular level and can sense the transient responses. Featuring a subwavelength optical element, near-field scanning optical microscopes display less than 50nm resolution along lateral directions. This capability to achieve high imaging resolution is critical to detect the positions and motions of dedicate samples such as proteins inside cells. However, the task is extremely challenging, not only because of the optical resolution limit, but also because of the requirement of high sensitivity for the systems.;We have explores the feasibility to excite and manipulate surface plasmon polaritons on metallic structures. The surface plasmon interference patterns possess subwavelength resolution with respect to free space light beam. A circular grating based plasmonic lens is studied for its ability of generation and focusing of SP waves, which provides us tight focus of ∼100 nm with one order higher enhancement.;Additional study shows by exciting both propagating surface plasmons and localized surface plasmons, better field confinement and higher local field enhancement (more than three orders) can be achieved with a design of particle enhanced plasmonic lens, which is essential for a lot of applications in the nanoscale science with visible light and regular illumination power.;To further explore the limit of optical imaging, we have developed an apertureless NSOM system with the ability to retrieve amplitude and phase information of the nearfield simultaneously. The system has been demonstrated with highest resolution of ∼15nm FWHM for a broad working wavelength bandwidth from visible to near infrared. The modification of energy transfer between fluorescent molecules by metallic nanoparticles is also studied as an extension for the plasmonic imaging and sensing applications. Near-field optical and plasmonic based imaging systems, including surface plasmon enhanced fluorescence and FRET, have the potential to become a powerful analytical tool for noninvasive optical probing of the local chemical and structural properties in the nanoscale. |
