K. Sathiyamoorthy

Surface plasmon enhancement in gold nanoparticles in the presence of an optical gain medium: an analysis

The localized surface plasmon (LSP) enhancement in a gold nanoparticle is demonstrated in this paper. The enhancement of LSP is influenced by both size and the dielectric gain medium surrounding the nanoparticles. The nanoparticle is found to induce plasmonic enhancement of varying degrees depending on its size, and it is inferred that a gold nanoparticle of size 60 nm exhibits the maximum LSP for 532 nm excitation. Singularity due to cancellation of SP loss by an infinite gain medium and LSP enhancement are studied using a pump-probe Rayleigh scattering experiment. Gold nanoparticles of average size 60 nm exhibit the lowest threshold power to observe Rayleigh scattering. Furthermore, compared with the bare nanoparticles, a 12.5 fold enhancement of LSP is observed when the nanoparticle of average size 60 nm is kept in the gain medium.

Measurement and contouring of micro-scale objects through integrated transillumination in a flexible fiber probe system

High-resolution measurement and contouring of objects with micro-scale sizes have been two of the research challenges in many areas, such as nondestructive testing and imaging, imaging of artifacts in MEMS, and lab-on-chip devices, as well as in biomedical imaging. In this context, we use a transillumination incorporated fiber probe imaging system to enable imaging of the targeted object in a single shot. It also enables positioning of the probe system to the region of interest for further fine analysis, thereby reducing the long scanning time faced by conventional approaches. The capability of the developed probe is illustrated using standard USAF resolution chart and fluorescent microspheres as test targets. The probe system has axial and lateral resolutions of about 16 μm and 144  lp/mm, respectively. This proposed probe scheme can potentially be employed as a viable diagnostic imaging methodology.

Photoacoustic Based Surface Plasmon Resonance Spectroscopy: An Investigation

The objective of this paper is to carry out photoacoustic investigation of surface plasmons, so as to explore the possibility of employing photoacoustic techniques in real time sensing based on plasmon resonance spectroscopy. Such sensors exploit the high sensitivity of the surface plasmon frequency to the refractive index of layers of adsorbed molecules on the surface. Generally the resonance conditions are influenced by the material adsorbed onto the thin metal film, which will be explored in this project. An in house developed photoacoustic technique is employed as the detection system and subsequent spectroscopic investigations.

Characteristics of stand-alone microlenses in fiber-based fluorescence imaging applications.

Microlens-ended fibers, which have found tremendous interest in the recent past, find potential biomedical applications, in particular, in endoscopic imaging. The work presented in this paper focuses on the stand-alone microlenses along with custom-fabricated specialty optical fiber, such as imaging fiber, for probe imaging applications. Stand-alone self-aligned microlenses have been fabricated employing microcompression molding and then attached at the end facet of imaging fiber. A detailed characterization of the fabricated microlens is carried and it demonstrates appropriate focusing ability, high fluorescence collection efficiency and imaging ability for biomedical applications. The surface roughness of the microlens is found to be 25 nm with a minimum spot size of 38 μm. The probe imaging system is found to be able to image the fluorescence microspheres of 10 μm size. The collection efficiency of the fiber probe with lens found to be enhanced by three times approximately.

Nanoring patterning using surface plasmon assisted photolithography

Achievable resolution of nano-rings, fabricated using commonly employed conventional mask based photolithography, is limited by diffraction of light. In this work conventional photolithography is modified to incorporate the phenomenon of surface plasmons to overcome the diffraction limit and thus to fabricate nano rings. Here, an embedded-amplitude mask based surface plasmon lithography is numerically investigated to conceptalize a noval methodology to fabricate the proposed nano-ring structure. Results of FDTD simulation shows sharp transmission peaks at the hole edges which could be recorded using suitable thinned photoresist to obtain nano ring structures.