Eric X. Jin

Obtaining super resolution light spot using surface plasmon assisted sharp ridge nanoaperture

Finite difference time domain computations is used to study surface plasmon (SP) excitation around C- and H-shaped ridge nanoapertures made in silver film. The SP enhances optical transmission, in addition to the transmission mechanism of the waveguide propagation mode and Fabry-Perot-like resonance. However, the near-field collimation of ridge aperture is found completely destroyed. On the other hand, using a bowtie-shaped aperture with sharp ridges made in silver, the loss of near-field collimation can be recovered. A super resolution optical spot with full width half magnitude as small as 12nm×16nm is achieved due to the resonant SP excitation localized at the tips of bowtie. Much higher field enhancement is also obtained compared to the bowtie aperture made in chromium.

Enhanced optical near field from a bowtie aperture

The enhanced optical near field from a bowtie aperture in an aluminum film is experimentally demonstrated using near-field scanning optical microscopy. The full width half magnitude near-field optical spot is determined to be about 65×34nm2 by 458nm argon ion laser illumination, which is seven times smaller than those obtained from square and rectangular apertures of the same opening area. Light concentration and transmission enhancement of bowtie apertures promise a highly efficient nanoscale light source for near-field optical applications.

Contact optical nanolithography using nanoscale C-shaped apertures

C-shaped ridge apertures are used in contact nanolithography to achieve nanometer scale resolution. Lithography results demonstrated that holes as small as 60 nm can be produced in the photoresist by illuminating the apertures with a 355 nm laser beam. Experiments are also performed using comparable square and rectangular apertures. Results show enhanced transmission and light concentration of C apertures compared to the apertures with regular shapes. Finite difference time domain simulations are used to design the apertures and explain the experimental results.

Design, fabrication, and characterization of nanometer-scale ridged aperture optical antennae

We investigate light concentration and field enhancement in nanometer-scale ridged aperture antennae. Resent numerical simulations have shown that nanoscale ridged apertures can concentrate light into nanometer domain. Most importantly, these ridge apertures also provide an optical transmission enhancement several orders of magnitude higher compared to regularly shaped nanoscale apertures. We employ the finite-difference time-domain (FDTD) method to design these apertures and fabricate them in thin metal films. A home-built near field scanning optical microscope (NSOM) is used to map the near-field intensity distribution of the light transmitted through these apertures. It is shown that the ridged apertures can produce a concentrated light spot far beyond the diffraction limit, with transmission enhancement orders of magnitude higher than regularly shaped apertures. Nanolithography applications of these nanoscale ridged aperture antennae are demonstrated.

Obtaining Subwavelength Optical Spots Using Nanoscale Ridge Apertures

Concentrating light into a nanometer domain is needed for optically based materials processing at the nanoscale. Conventional nanometer-sized apertures suffer from low light transmission, therefore poor near-field radiation. It has been suggested that ridge apertures in various shapes can provide enhanced transmission while maintaining the subwavelength optical resolution. In this work, the near-field radiation from an H-shaped ridge nanoaperture fabricated in an aluminum thin film is experimentally characterized using near-field scanning optical microscopy. With the incident light polarized along the direction across the gap in the H aperture, the H aperture is capable of providing an optical spot of about 106 nm by 80 nm in full-width half-maximum size. which is comparable to its gap size and substantially smaller than those obtained from the square and rectangular apertures of the same opening area. Finite different time domain simulations are used to explain the experimental results. Variations between the spot sizes obtained from a 3 X 3 array of H apertures are about 4-6%. The consistency and reliability of the near-field radiation from the H apertures show their potential as an efficient near-field light source for materials processing at the nanoscale.

Enhancement of optical transmission through planar nanoapertures in a metal film

The optical transmission mechanism through a ridge nano-aperture in a metal film is discussed based on the waveguide theory and FDTD computations. The transmission enhancement through ridge apertures is associated with the TE10 waveguide propagation mode. In terms of near and far field radiator, the ridge aperture can be represented as a combination of an oscillating electric dipole and two magnetic dipoles. The effects of localized surface plasmon (LSP) excited on the edges of ridge nano-apertures made in silver are discussed. The transmission enhancement and field concentration functions of ridge apertures are confirmed by contact lithography experiments.

Concentrating light into nanometer domain using nanoscale ridge apertures and its application in laser-based nanomanufacturing

In this work, we investigate light concentration in nanoscale ridge apertures and its applications in nanomanufacturing. Optical transmission of ridge apertures in a metal film is optimized by numerical design using the finite-difference time-domain (FDTD) method. We show that ridge apertures provide an optical transmission enhancement of several orders of magnitude higher than regularly shaped nanoscale apertures, and also confine the transmitted light to nanoscale dimensions. We fabricated these ridge apertures in metal film coated on quartz substrates by focused ion beam (FIB) milling. These apertures are characterized by nearfield scanning optical microscopy (NSOM). The ridge apertures are also used as a nanoscale light source for nanolithography. Holes with sub-100 nm dimensions are produced in the photoresist with visible and UV laser illuminations. The performance of the ridge apertures is compared with that of regular nanoscale apertures to demonstrate their advantages and promising potentials for many near-field optical applications.

Nanolithography Using High Transmission Nanoscale Ridge Apertures

In this paper, we describe using high transmission nanoscale apertures of C and H shapes for nanolithography applications. We demonstrate that these ridge apertures provide a highly localized and intense light spot that can be used in lithography experiments.Copyright

Near and Far Field Experiments of Power Transfer by Mode Beating in Plasmonic Devices

Heat assisted magnetic recording (HAMR) requires a sufficiently small heat spot, which is much below the diffraction limit of the wavelength of the used light. This can be achieved with an optical near field source consisting of a small metallic wedge which supports edge plasmons. The power transfer between a dielectric rectangular waveguide and this metallic wedge is investigated in simulations and experiments. Beating of two eigenmodes of this system leads to power oscillations between the waveguide core and the edge plasmon along their overlap length. This was confirmed in near field experiments which are based on the evaporation of phase change material with the absorbed optical near fields as heat source. Devices with weak and strong edge plasmon excitation could be clearly distinguished in a simple far field experiment.

Plasmonic-Enhanced Radiative Transfer Through Nanoscale Aperture Antennas

Nanoscale ridge aperture antenna as a nanoscale high transmission optical device is demonstrated. High transfer efficiency and confined radiation are achieved simultaneously in the near field compared with regularly-shaped apertures. The radiation enhancement is attributed to the fundamental electromagnetic field propagating in the TE10 mode concentrated in the gap between the ridges. The transfer efficiency is further enhanced through plasmon excitation and resonance. This paper reports spectroscopic measurements of radiative transfer through bowtie shape ridge aperture antennas. Resonance in these aperture antennas and its relation with the aperture geometry are investigated. The near-field radiation through the bowtie aperture and the regular nanoaperture is also mapped with near-field scanning optical microscopy. It is revealed that plasmon excitation and resonance contribute to the radiation enhancement through the ridge aperture antennas.Copyright