Plasmonic metamaterial

A plasmonic metamaterial is a metamaterial that uses surface plasmons to achieve optical properties not seen in nature. Plasmons are produced from the interaction of light with metal-dielectric materials. Under specific conditions, the incident light couples with the surface plasmons to create self-sustaining, propagating electromagnetic waves known as surface plasmon polaritons (SPPs). Once launched, the SPPs ripple along the metal-dielectric interface. Compared with the incident light, the SPPs can be much shorter in wavelength. The properties stem from the unique structure of the metal-dielectric composites, with features smaller than the wavelength of light separated by subwavelength distances. Light hitting such a metamaterial is transformed into surface plasmon polaritons, which are shorter in wavelength than the incident light. Plasmonic materials Plasmonic materials are metals or metal-like materials that exhibit negative real permittivity. Most common plasmonic mat

Investigation of photoinduced effects in plasmonic nanocavities

Aqeel Ahmed

Light matter interaction can be boosted by several orders of magnitude by tailoring the photonic environment, thus enabling a wide range of applications. One particular example are plasmonic nanostructures that support localized surface plasmon polariton (LSPP) leading to enhancement and confinement of incident electromagnetic fields. These novel properties provide access to a large number of optically driven effects within matter placed in the vicinity of such nanostructures. In this thesis, we investigate the effects of optical excitation on gold nanostructures in the presence of Raman active molecules. This is accomplished by fabricating nanoparticle on mirror (NPoM) plasmonic nanostructures where a gold nanoparticle is placed at a fixed distance from a smooth gold film using molecular monolayers. As the nanoparticle and mirror are placed only a few nanometers apart, optical excitation leads to formation of hybridized LSPP modes due to coupling between the plasmons within the nanoparticle and the mirror. This plasmonic coupling also results in confinement and subsequent enhancement of the incident light within the gap and is extremely sensitive to structural parameters of the NPoM. The creation of a homogeneous gap between the nanoparticle and mirror is quite challenging due the roughness of the mirror. Moreover, due to the large number of NPoM nanostructures present on the sample it is quite difficult to locate a specific NPoM. To bypass these difficulties atomically smooth and patterned substrates were developed using template stripping combined with conventional photolithography techniques. Next, in order to characterize the optical response of the NPoMs, a custom optical setup was built. The setup was primarily designed to investigate the plasmonic properties of the NPoM using elastic scattering spectroscopy along with surface enhanced Raman scattering (SERS) from the molecules within the gap. The combination of these two techniques was later used to investigate the effect of laser power on the NPoMs. It was discovered that the scattering spectra of the NPoMs changed irreversibly after laser exposure even with a few ÎŒW/ÎŒm2 incident intensities. Moreover, the plasmonic response of the NPoMs fabricated with well organized molecular monolayer changed much faster than the NPoMs prepared with disorganized ones. This phenomenon was also investigated in NPoMs prepared using a dielectric gap layer, by changing the gap conductivity, and by changing the nanoparticle shape. The experimental results combined with simulations suggest a decrease in gap height due to the reorientation of the molecular monolayer under optical excitation.

EPFL2021

Nanoparticle on mirror plasmonic nanostructure for molecular cavity optomechanics

Aqeel Ahmed, Christophe Marcel Georges Galland, Nils Kipfer, Tianqi Zhu

The plasmonic response of gold can be utilized to enhance the incident electromagnetic (EM) field by several orders of magnitude. When a gold nanoparticle is placed in close proximity to a gold film, the incident field can excite a deeply confined plasmon, strongly enhancing the Raman interaction with molecules placed within the gap. Recent theoretical predictions suggest the suitability of such arrangements to optically amplify the internal vibrations of molecules. This paper presents the fabrication and characterization of such plasmonic nanocavities.

IEEE2018

Investigation of photoinduced effects in plasmonic nanocavities

Aqeel Ahmed

EPFL2021

Investigation of photoinduced effects in plasmonic nanocavities

Nanoparticle on mirror plasmonic nanostructure for molecular cavity optomechanics

Internal forces in plasmonic metamaterials

Internal forces in plasmonic metamaterials

Investigation of photoinduced effects in plasmonic nanocavities

Nanoparticle on mirror plasmonic nanostructure for molecular cavity optomechanics