A near‐field optical technique, using a new type of solid immersion lens (SIL), has been developed and applied to the writing and reading of domains in magneto‐optic material. The SIL is a truncated glass sphere which serves to increase the numerical aperture of the optical system by n2, where n is the index of refraction of the lens material. Using a SIL made from n=1.83 glass and illuminating with 780 nm light, we have achieved a 317 nm spot size. We have resolved a 500 nm period grating, and written and read 350 nm diameter magnetic domains. The technique should be capable of a 125 nm focused spot size using blue light.

Near‐field optical data storage using a solid immersion lens

In this article we review the use of near-field photonics for trapping, transport and handling of nanomaterials. While the advantages of traditional optical tweezing are well known at the microscale, direct application of these techniques to the handling of nanoscale materials has proven difficult due to unfavourable scaling of the fundamental physics. Recently a number of research groups have demonstrated how the evanescent fields surrounding photonic structures like photonic waveguides, optical resonators, and plasmonic nanoparticles can be used to greatly enhance optical forces. Here, we introduce some of the most common implementations of these techniques, focusing on those which have relevance to microfluidic or optofluidic applications. Since the field is still relatively nascent, we spend much of the article laying out the fundamental and practical advantages that near field optical manipulation offers over both traditional optical tweezing and other particle handling techniques. In addition we highlight three application areas where these techniques namely could be of interest to the lab-on-a-chip community, namely: single molecule analysis, nanoassembly, and optical chromatography.

Nanomanipulation using near field photonics

We have exposed 190 nm lines in photoresist by focusing a laser beam (λ=442 nm) in a solid immersion lens (SIL) that is mounted on a flexible cantilever and scanned by a modified commercial atomic force microscope. The scan rate was 1 cm/s, which is several orders of magnitude faster than typical reports of near-field lithography using tapered optical fibers. The enhanced speed is a result of the high optical efficiency (about 10−1) of the SIL. Once exposed with the SIL, the photoresist was developed and the pattern was transferred to the silicon substrate by plasma etching.

Near-field photolithography with a solid immersion lens

We present a high-spatial-resolution subsurface microscopy technique that significantly increases the numerical aperture of a microscope without introducing an additional spherical aberration. Consequently, the diffraction-limited spatial resolution is improved beyond the limit of standard subsurface microscopy. By realizing a numerical aperture of 3.4, we experimentally demonstrate a lateral spatial resolution of better than 0.23 μm in subsurface inspection of Si integrated circuits at near infrared wavelengths.

High spatial resolution subsurface microscopy

We describe a new type of optical pickup for use in high-density optical storage systems. By changing a conventional pickup design to include a glass element between the objective and the disk, the transverse resolution of the system can be increased by as much as a factor of 1.5. This system is also less sensitive than conventional systems to variations in disk thickness and disk tilt. We demonstrate how the system has been used as a microscope to inspect an optical disk and describe possible design configurations for an optical pickup.

High-numerical-aperture lens system for optical storage

We have developed an electro-optic cell as a fine-adjustment focusing system for an optical disk. The cell is fabricated from transparent lead lanthanum zirconate titanate ceramic and has concentric-patterned indium tin oxide electrodes. The electro-optic cell can generate a relative phase shift in the pupil function. We have confirmed, theoretically and experimentally, that the phase shift induces a change in focal position that is as much as twice the focal depth without degrading the region near the main lobe of the point-spread function.

K. Osato

Papers

High-numerical-aperture lens system for optical storage

Electro-optic focusing system for a high-density optical disk