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SummaryWe investigate the ability of the bow-tie slot antenna to generate intense optical spots below the diffraction limit. A commercially available finite-difference time-domain electromagnetic modelling software is used in the numerical simulations. The finite-difference time-domain software is first compared to analytical results at optical frequencies to verify its accuracy. We then present numerical simulations for various geometries involving apertures on thin films and the bowtie antenna. The transmission efficiency and optical spot size of the bow-tie antenna are compared with those of rectangular and circular apertures on thin metal films. We also investigate the effects of material composition, frequency, and antenna geometry on the near-field radiation pattern using numerical simulations.

The performance of the ridge waveguide as a near-field aperture in data storage systems is investigated. Finite element method (FEM) and finite-difference time-domain (FDTD) based software are used in the numerical simulations. To verify their accuracy at optical frequencies, the FEM and FDTD are first compared to analytical results. The accuracy of these techniques for modeling ridge waveguides at optical frequencies is also evaluated by comparing their results with each other for a plane wave illumination. The FEM, which is capable of modeling focused beams, is then used to simulate various geometries involving ridge waveguides. Near-field radiation from ridge waveguide transducer is expressed in terms of power density quantities. Previous studies in the literature consider the performance of the transducer in free space, rather than in the presence of a recording magnetic medium. The effect of the recording magnetic medium on the transmission efficiency and spot size is discussed using numerical simulations. The effect of various geometric parameters on the optical spot size and transmission efficiency is investigated and discussed. Based on our numerical simulations, a promising transducer design is suggested to obtain intense optical spots well below the diffraction limit. Numerical simulations suggest that a full width at half maximum spot diameter of 31nm in the recording magnetic medium can be obtained. The maximum value of the absorbed optical power density in the recording medium is about 1.67×10−4mW∕nm3 for a 100mW input power. In-track and cross-track profiles for this design are compared with Gaussian distributions.

Heat-or thermally assisted magnetic recording employing perpendicular media is considered. The technological and physical principles treated are also applicable to longitudinal recording. Three issues are treated: Optical heating of a small volume of the medium on the length scale of a recorded bit at areal densities beyond 1 Tb/in 2 , dissipation of waste heat generated on an integrated flying slider, and optimization of the recording process.

A near-field optical system is investigated to improve the transmission efficiency of near-field transducers. A ridge waveguide is placed adjacent to a solid immersion lens (SIL) but separated by a low-index dielectric layer. The incident electric field near the focus of the SIL is determined by the Richards-Wolf vector field equations. The finite element method is used to solve Maxwell's equations. A spot size of 31 nm is obtained. The maximum value of the absorbed optical power density in the recording medium is 7.51 x 10(-4) mW/nm3 for a 100 mW input power.

Six-particle and eight-particle common-gap plasmonic nanoantennas are utilized to obtain a broadband spectral response when illuminated with circular and elliptical polarization. Due to the insensitivity of dipole antennas to circular polarization, the resonant structures are brought together around the common-gap to expand the spectrum of the whole system. Their ability to focus light at different frequencies is demonstrated. The spectral response is manipulated by geometrical parameters and the strength of the spectral peaks is tailored through the ellipticity of the elliptically polarized light.

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Radiative cooling is potentially one of the most innovative approaches to reducing energy density in buildings and industry, as well as achieving higher levels of energy efficiency. Several studies have reported the design of spectrally selective layered structures for daytime passive radiative cooling. However, a comprehensive design of such systems requires the spectral behavior of different materials and radiative heat transfer mechanisms to be addressed together. Here, we introduce a design methodology for daytime passive radiative cooling with thin film filters which accounts for the spectral tailoring at the visible and infrared spectrum. The major difference of this method is that it does not require a predefined target ideal emittance. The results show that higher cooling powers are possible compared to the previously reported thin-film structures, which were designed from a purely spectral perspective. The underlying mechanisms of the resulting spectral profiles, which give rise to improved performance, are investigated by wave impedance analysis. Cooling powers up to 100 W / m 2 are obtained with seven layers on Ag. The findings of this study indicate that structures with better performance in terms of cooling powers and temperature reduction rates can be obtained following the procedure discussed.