Plasmonic Implanted Nanogrooves for Optical Beaming.

Surface plasmon polaritons are electromagnetic surface waves, which, due to their nanoscale nature, are efficiently used for modifying an output of optical field through a metallic nanoslit, e.g., extraordinary optical transmission and beaming of light. Herein, the phenomenon of optical beaming by employing a regular array of semicylinder-shaped grooves around a nanoslit has been investigated based on numerical simulations. By analyzing the behavior of Poynting vectors in near surroundings of the slit, we have successfully demonstrated that grooves which are embedded on the layer at the exit side of the slit produce enhanced directionality of the output light than the unembedded ones. In case of semicylinder-shaped grooves, the calculated intensity of the output beam was 1.5-times, at near and far distances, higher than that of the grating grooves. Our analysis shows that positioning of the groove right at the exit of the slit is crucial for the enhancement of the beaming effect. This is due to the conversion of surface plasmon polaritons into a freely propagating field and the possible excitation of localized surface plasmons because of the presence of nanogroove. Furthermore, the proposed geometries are made of Aluminum, which is a plasmonic material and commonly applied for the fabrication of optical nanostructures. Manipulating of light (beaming, focusing/guiding, and splitting) by nanoslit can be beneficial to several applications such as nano-resolution optical imaging, sensors, and plasmonic circuits.

Surface Plasmons Carry the Pancharatnam-Berry Geometric Phase.

Surface plasmon polaritons (SPPs) are electromagnetic surface waves that travel along the boundary of a metal and a dielectric medium. They can be generated when freely propagating light is scattered by structural metallic features such as gratings or slits. In plasmonics, SPPs are manipulated, amplified, or routed before being converted back into light by a second scattering event. In this process, the light acquires a dynamic phase and perhaps an additional geometric phase associated with polarization changes. We examine the possibility that SPPs mediate the Pancharatnam-Berry phase, which follows from a closed path of successive in-phase polarization-state transformations on the Poincaré sphere and demonstrate that this is indeed the case. The geometric phase is shown to survive the light→SPP→light process and, moreover, its magnitude agrees with Pancharatnam's rule. Our findings are fundamental in nature and highly relevant for photonics applications.

Dynamic control of optical transmission through a nano-slit using surface plasmons.

We demonstrate how the optical transmission by a directly illuminated, sub-wavelength slit in a metal film can be dynamically controlled by varying the incident beam's phase relative to that of a stream of surface plasmon polaritions which are generated at a nearby grating. The transmission can be smoothly altered from its maximum value to practically zero. The results from a simple model and from rigorous numerical simulations are in excellent agreement with our experimental results. Our method may be applied in all-optical switching.

Uniform distribution of Ag particles upon imprinted polymer grating for Raman signal enhancement.

Surface Enhanced Raman Scattering (SERS) is gaining popularity among analytical methods in biosciences and sensor technology since it provides high specificity, non-destructiveness, and the unique fingerprint spectra of the molecules. Historically, glass has been the primary choice as a substrate for SERS, but polymers are attractive due to their plasticity, ease of handling, and their low cost. Herein, the performance of cyclo olefin polymer (COP) as a substrate with 1D subwavelength modulations combined with silver nanoparticles is studied for SERS measurements. These 1D grating structures on polymer are fabricated by hot embossing method followed by deposition of silver nanoparticles (AgNPs) using the drop-casting method. Spatial variations of the substrate surface have been reduced by providing a consistent distribution of hot-spots. We present an analysis of the surface uniformity related to the distribution of Ag particles. We achieve around 8-fold Raman signal enhancements with improved reproducibility in comparison to smooth, unmodulated surfaces with AgNPs. This method of fabrication of SERS substrates is simple and inexpensive compared to the thermal evaporation method (TEM) of metallic layer deposition. It also helps to control the tarnishing effect on metallic surfaces due to silver deposition prior to Raman measurements. This kind of polymer gratings combined with AgNPs have potential applications in medical, biological and chemical sensing, where Raman signal enhancement with high reproducibility is required.