Enhancing the Efficiency of Slit-Coupling to Surface-Plasmon Polariton via Dispersion Engineering

We describe a simple method for enhancing the efficiency of coupling from a free-space transverse-magnetic (TM) plane-wave mode into a surface-plasmon-polariton (SPP) mode. The coupling structure consists a metal film with a dielectric-filled slit and a planar, dielectric layer on the slit-exit side of the metal film. By varying the dielectric layer thickness, the wavevector of the SPP mode on the metal surface can be tuned to match the wavevector magnitude of the modes emanating from the slit exit, enabling high-efficiency radiation coupling into the SPP mode at the slit exit. An optimal dielectric layer thickness of approximately 100 nm yields a visible-frequency SPP coupling efficiency approximately 4 times greater than the SPP coupling efficiency without the dielectric layer. Commensurate coupling enhancement is observed spanning the free-space wavelength range 400 nm < or = lambda(0) < or = 700 nm. We map the dependence of the SPP coupling efficiency on the slit width, the dielectric-layer thickness, and the incident wavelength to fully characterize this SPP coupling methodolog

Investigation of Machining Parameters for Multiple Response Optimization in Microelectrodischarge Milling

This paper investigated the influence of three micro electrodischarge milling process parameters, which were feed rate, capacitance, and voltage. The response variables were average surface roughness (Ra), maximum peak-to-valley roughness height (Ry), tool wear ratio (TWR), and material removal rate (MRR). Statistical models of these output responses were developed using three-level full factorial design of experiment. The developed models were used for multiple-response optimization by desirability function approach to obtain minimum Ra, Ry, TWR, and maximum MRR. Maximum desirability was found to be 88%. The optimized values of Ra, Ry, TWR, and MRR were 0.04, 0.34 μm, 0.044, and 0.08 mg min−1, respectively for 4.79 μm s−1 feed rate, 0.1 nF capacitance, and 80 V voltage. Optimized machining parameters were used in verification experiments, where the responses were found very close to the predicted values

Surface roughness analysis of beryllium-copper alloy in micro end milling

In this paper, the effect of feed per tooth and depth of cut during micro end milling of beryllium-copper alloy, a mold material, has been analyzed. Central composite design, a response surface method, was used to statistically analyze the influence of these process parameters on the surface roughness. The interaction effect of parameters was also discussed. Statistical models for micro-end-milling were established to predict the average (Ra), maximum (Ry) and ten-point (Rz) surface roughness. Ra was found strongly influenced by feed while, Ry was influenced by the interaction effects of feed and depth of cut. Rz was influenced by both feed and the interaction of feed and depth of cut. Surface roughness in the range of 0.10 - 0.20 μm was observed

Novel routes to electromagnetic enhancement and its characterisation in surface- and tip-enhanced Raman scattering

Quantitative understanding of the electromagnetic component in enhanced Raman spectroscopy is often difficult to achieve on account of the complex substrate structures utilised. We therefore turn to two structurally simple systems amenable to detailed modelling. The first is tip-enhanced Raman scattering under electron scanning tunnelling microscopy control (STM-TERS) where, appealing to understanding developed in the context of photon emission from STM, it is argued that the localised surface plasmon modes driving the Raman enhancement exist in the visible and near-infrared regime only by virtue of significant modification to the optical properties of the tip and sample metals (gold here). This is due to the strong dc field-induced (∼109V m−1) non-linear corrections to the dielectric function of goldviathe third order susceptibility term in the polarisation. Also, sub-5 nm spatial resolution is shown in the modelling. Secondly, we suggest a novel deployment of hybrid plasmonic waveguide modes in surface enhanced Raman scattering (HPWG-SERS). This delivers strong confinement of electromagnetic energy in a ∼10 nm oxide ‘gap’ between a high-index dielectric material of nanoscale width (a GaAs nanorod and a 100 nm Si slab are considered here) and a metal, yielding a monotonic variation in the Raman enhancement factor as a function of wavelength with no long-wavelength cut-off, both features that contrast with STM-TERS.</p

Investigation of Finish-cut of Microelectrodischarge Milling for Nano Surface Finish

In this paper the machining condition to achieve nano surface roughness in finish cut micro electro discharge milling was investigated. The effect of feed rate and capacitance were studied on average surface roughness (Ra), and maximum peak-to-valley roughness height (Ry). Statistical models were developed using three-level twofactor experimental design. Ra and Ry were minimized using desirability function approach. The value of desirability was found to be 98%. The minimum values of Ra and Ry were 23 nm and 173 nm respectively for 1.00 μm s-1 feed rate, 0.01 nF capacitance and 80 volts voltage. Verification experiments were conducted to check the accuracy of the model, where the responses were found very close to the predicted values. The developed models can be used to generate nano surface finish for various microstructures