There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

The unprecedented ability of nanometallic (that is, plasmonic) structures to concentrate light into deep-subwavelength volumes has propelled their use in a vast array of nanophotonics technologies and research endeavours. Plasmonic light concentrators can elegantly interface diffraction-limited dielectric optical components with nanophotonic structures. Passive and active plasmonic devices provide new pathways to generate, guide, modulate and detect light with structures that are similar in size to state-of-the-art electronic devices. With the ability to produce highly confined optical fields, the conventional rules for light-matter interactions need to be re-examined, and researchers are venturing into new regimes of optical physics. In this review we will discuss the basic concepts behind plasmonics-enabled light concentration and manipulation, make an attempt to capture the wide range of activities and excitement in this area, and speculate on possible future directions.

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Plasmonics for extreme light concentration and manipulation.

Recent years have seen a rapid expansion of research into nanophotonics based on surface plasmon–polaritons. These electromagnetic waves propagate along metal–dielectric interfaces and can be guided by metallic nanostructures beyond the diffraction limit. This remarkable capability has unique prospects for the design of highly integrated photonic signal-processing systems, nanoresolution optical imaging techniques and sensors. This Review summarizes the basic principles and major achievements of plasmon guiding, and details the current state-of-the-art in subwavelength plasmonic waveguides, passive and active nanoplasmonic components for the generation, manipulation and detection of radiation, and configurations for the nanofocusing of light. Potential future developments and applications of nanophotonic devices and circuits are also discussed, such as in optical signals processing, nanoscale optical devices and near-field microscopy with nanoscale resolution.

Plasmonics beyond the diffraction limit

Optical antennas are devices that convert freely propagating optical radiation into localized energy, and vice versa. They enable the control and manipulation of optical fields at the nanometre scale, and hold promise for enhancing the performance and efficiency of photodetection, light emission and sensing. Although many of the properties and parameters of optical antennas are similar to their radiowave and microwave counterparts, they have important differences resulting from their small size and the resonant properties of metal nanostructures. This Review summarizes the physical properties of optical antennas, provides a summary of some of the most important recent developments in the field, discusses the potential applications and identifies the future challenges and opportunities.

Antennas for light

Recent years have seen a growing interest in using metal nanostructures to control temperature on the nanoscale. Under illumination at its plasmonic resonance, a metal nanoparticle features enhanced light absorption, turning it into an ideal nano-source of heat, remotely controllable using light. Such a powerful and flexible photothermal scheme is the basis of thermo-plasmonics. Here, the recent progress of this emerging and fast-growing field is reviewed. First, the physics of heat generation in metal nanoparticles is described, under both continuous and pulsed illumination. The second part is dedicated to numerical and experimental methods that have been developed to further understand and engineer plasmonic-assisted heating processes on the nanoscale. Finally, some of the most recent applications based on the heat generated by gold nanoparticles are surveyed, namely photothermal cancer therapy, nano-surgery, drug delivery, photothermal imaging, protein tracking, photoacoustic imaging, nano-chemistry and optofluidics.

http://www.guillaume.baffou.com/publications/020-Baffou-LPR.pdf

Thermo‐plasmonics: using metallic nanostructures as nano‐sources of heat

Heat-assisted magnetic recording is a promising approach for enabling large increases in the storage density of hard disk drives. A laser is used to momentarily heat the recording area of the medium to reduce its coercivity below that of the applied magnetic field from the recording head. In such a system, the recording materials have a very high magnetic anisotropy, which is essential for the thermal stability of the magnetization of the extremely small grains in the medium. This technology involves new recording physics, new approaches to near field optics, a recording head that integrates optics and magnetics, new recording materials, lubricants that can withstand extremely high temperatures, and new approaches to the recording channel design. This paper surveys the challenges for this technology and the progress that has been made in addressing them.

Heat Assisted Magnetic Recording

Although near-field microscopy has allowed optical imaging with sub-20 nm resolution, the optical throughput of this technique is notoriously small. As a result, applications such as optical data storage have been impractical. However, with an optimized near-field transducer design, we show that optical energy can be transferred efficiently to a lossy metallic medium and yet remain confined in a spot that is much smaller than the diffraction limit. Such a transducer was integrated into a recording head and flown over a magnetic recording medium on a rotating disk. Optical power from a semiconductor laser at a wavelength of 830 nm was efficiently coupled by the transducer into the medium to heat a 70-nm track above the Curie point in nanoseconds and record data at an areal density of ∼375 Tb m−2. This transducer design should scale to even smaller optical spots. Using a near-field transducer with efficient optical energy transfer, researchers demonstrate proof-of-principle heat-assisted magnetic recording with multi-track data density of ∼375 Tb m−2.

Heat-assisted magnetic recording by a near-field transducer with efficient optical energy transfer

Due to the limits of conventional perpendicular magnetic recording, it appears that alternative technologies are needed at areal densities >500 Gb/in2. Heat-assisted magnetic recording (HAMR) is a promising approach to extend areal densities to 1 Tb/in2 and beyond. All of the unique components necessary for a working HAMR system have been demonstrated. Although HAMR permits writing on high Hc media with lower magnetic fields and can produce higher write gradients than conventional magnetic recording, head/media spacing and the development of high Hc media with small grains remains challenging

Heat-Assisted Magnetic Recording

Scaling the areal density, while maintaining a proper balance between media signal-to-noise ratio, thermal stability, and writability, will soon require an alternative recording technology. Heat assisted magnetic recording (HAMR) can achieve this balance by allowing high anisotropy media to be written by heating the media during the writing process (e.g., by laser light) to temporarily lower the anisotropy. Three major challenges of designing a HAMR head that tightly focuses light and collocates it with the magnetic field are discussed: 1) magnetic field delivery; 2) optical delivery; and 3) magnetic and optical field delivery integration. Thousands of these HAMR heads were built into sliders and head-gimbal assemblies, and optical and scanning electron micrograph images are shown. Scanning near-field optical microscopy (SNOM) characterization of the HAMR head shows that the predicted ~ lambda/4 full-width half-maximum (FWHM) spot size can be achieved using 488 nm light (124 nm was achieved). SNOM images also show that wafer level fabricated apertures were able to effectively eliminate sidelobes from the focused spot intensity profile. A magnetic force microscopy image of HAMR media shows that non-HAMR (laser power off) was not able to write transitions in the HAMR specific media even at very high write currents, but transitions could be written using HAMR (laser power on), even at lower write currents. A cross-track profile is shown for a fully integrated HAMR head where the magnetic pole physical width is ~350 nm, but the written track is ~200 nm, which demonstrates HAMR. A HAMR optimization contour shows that there is an optimum write current and laser power and that simply going to the highest write current and laser power does not lead to the best recording. Lastly, some prospects for advancing HAMR are given and a few key problems to be solved are mentioned.

Integrated Heat Assisted Magnetic Recording Head: Design and Recording Demonstration

Electron beam lithography presents a great opportunity for bit-patterned media (BPM) applications due to its resolution capability and placement accuracy. However, there are still many challenges associated with this application including tool availability, resist capability, process development, and associated metrology needs. This paper will briefly discuss these challenges and show the results of sub-25 nm pitch (1 Tdots∕in.2) patterning from both a simulation and experimental perspective. The simulation results indicate that the energy contrast between the exposed and unexposed areas goes down quickly as the pitch size gets smaller and smaller, making it more difficult for image formation of high-resolution dot patterning. The strategy to overcome this issue is to optimize the development process, which aims at increasing the resist contrast and enlarging the process window. By using this approach, the authors have successfully demonstrated a pitch resolution down to 18 nm for a positive-tone resist Z...

Robert Earl Rottmayer

Papers

Heat Assisted Magnetic Recording

Heat-assisted magnetic recording by a near-field transducer with efficient optical energy transfer

Heat-Assisted Magnetic Recording

Integrated Heat Assisted Magnetic Recording Head: Design and Recording Demonstration

Challenges in 1 Teradot∕in.2 dot patterning using electron beam lithography for bit-patterned media