Excitation Of Surface Plasmon Waves Research Articles

Optical-fiber surface-plasmon-resonance sensor employing long-period fiber gratings in multiplexing

A new type of optical-fiber surface-plasmon-resonance (SPR) sensor based on a thin metallic film and long-period fiber gratings for measuring small changes of refractive index of analyte is presented. This sensor simply employs a long-period fiber grating with a proper period to couple a core mode (HE11) to the copropagating cladding mode that can excite a surface-plasmon wave (SPW). The mainly theoretical base used to analyze this new structure is the unconjugated form of coupled-mode equations. In this new SPR sensor, the variation of the refractive index of analyte is determined by monitoring the change of the transmitted core mode power, which is calculated by unconjugated two-mode coupled-mode equations at a fixed wavelength. The numerical results have demonstrated that this new and simple configuration may be used as a highly sensitive amplitude sensor. As far as the excitation of SPW, the model of numerical simulation, and the complexity of measurement equipment are concerned, this new structure is superior to the proposed sensor, consisting of a bent polished single-mode SPR optical fiber. Furthermore, the structure can be easily adapted for a SPR fiber optical probe if a mirror is deposited on the fiber tip.

Nanofiber optic sensor based on the excitation of surface plasmon wave near fiber tip

We present a sensitive nano-optical fiber biosensor made by shaping a fiber to form a taper with a tip size under 100 nm. A 40-nm-thick layer of gold is coated around the tapered fiber and a surface plasmon wave is excited near the tip to achieve a sensitivity of the reflective index unit of approximately 4000 (% RIU(-1)) in the intensity measurement. A 3-D coded finite-difference time-domain approach verifies the excitation of the surface plasmon wave and the differences among its intensities in media of various refractive indices. The nanotip fiber sensor has the merits of a low background light and an ultrasmall detection region. Only a microliter of sample solution is required for detection.

Generation of 0.4-keV Femtosecond Electron Pulses using Impulsively Excited Surface Plasmons

We demonstrate the generation of 0.4-keV, sub-27 fs electron pulses using low-intensity laser pulses from a Ti:sapphire oscillator through the excitation of surface plasmon waves on a time scale within the plasmon lifetime. Modeling of the ponderomotive electron pulse acceleration yields electron energy spectra that are in excellent agreement with the observed ones. Our work opens a doorway for time-resolved experimentation using low-power, high-repetition rate laser pulses.

Compact surface plasmon resonance-transducers with spectral readout for biosensing applications

Surface plasmon resonance (SPR) has become an important tool in sensing applications. The most abundant set-up records surface plasmon excitation for monochromatic light as a function of the angle of incidence. This requires imaging systems and makes the overall set-up bulky. An alternative is spectrally resolved SPR, which allows to separate sensor and signal analysis. One approach is based on the excitation of surface plasmon waves on the surface of a declad optical fibre. This allows an elegant probe-type geometry, but is less desirable under manufacturing and liquid handling aspects. We have investigated the possibility to develop compact SPR-probes combining spectral SPR and a planar sensor geometry. Two miniaturised set-ups were compared to a classical optical-bench device. Performance was assessed by use of the devices as a refractometer. Results were confirmed by two bioassays: (i) by a protein multilayer system consisting of a biotin-albumin-conjugate and polystreptavidin; and (ii) by monitoring the interaction of thrombin and an immobilised thrombin-inhibitor. All set-ups showed good long term stability. Noise values from refractometry were in good agreement with bioassays, for the classical set-up, but increased noise levels were observed for the miniaturised set-ups indicating a requirement for improved mechanical device stability.

Experimental investigation of lateral wave contribution to the shift of a reflected beam at surface plasmon resonance

Reflected field intensity distributions are reported for surface plasmon wave excitation in an attenuated total internal reflection configuration for different metal film thickness. The measured lateral shift is compared with theoretical predictions.

Determination of the infrared optical constants of highly reflecting materials by means of surface plasmon excitation-application to Pd

Describes a new method of determination of the complex dielectric constant in the infrared for highly reflecting metals, which takes advantage of the excitation of surface plasmon waves at the metal/air interface. The authors present and discuss the results obtained by this method for Pd, on carefully characterised evaporated films, and the new features which show up in the absorption spectrum.