John M. Guerra

Photon tunneling microscopy

Photons incident to a total internal reflection surface that is also the object plane of a reflected light microscope will tunnel through a submicron gap in the presence of a dielectric sample. Tunneling increases exponentially with sample height for a homogeneous refractive index and is quantified by empirical calibration to a known geometry. Video photometry of the grays scale tunneling image is converted by a three-axis oscilloscope into a real time 3-D topographic image featuring variable perspective. Vertical resolution is detector-limited to less than a nanometer over a field depth, also detector-limited, of ~0.75lambda; lateral resolution is enhanced to ~0.29lambda. Photon tunneling images of diamond turned surfaces, optical data structures, a polished optical surface, and microlithographic structures are among those presented. Comparison and correlation with other methods for measuring surface topography in this regime are briefly discussed.

Photon Tunneling Microscopy of Polymeric Surfaces

With photon tunneling microscopy it is possible to image polymeric and other dielectric surfaces by means of the unusual properties of photon tunneling or evanescent waves. Vertical resolution is 1 nanometer, limited by the detector, over a vertical range of half a wavelength. Lateral resolution is better than a quarter of a wavelength over a field of view up to 125 micrometers. Samples can be surveyed in real time in air, with no need for metallization, and without shadowing or the intrusive effects of electrons or scanning probes. The use of this technique to study single crystals of polyethylene and processes such as latex film formation and the evolution of polystyrene topography while dewetting above the glass transition temperature are described.

A Practical Total Integrated Scatterometer

Universal acceptance of a proposed standard measurement method can depend not only upon how soundly it is based in scientific theory but on its cost and technical implementation as well. A total integrated scatterometer for the optical shop is described with emphasis on economy, rapid measurement, repeatability, and ergonomic packaging as controlling design criteria. The advent of low-cost microvolt resolution in digital multimeters allows the use of large-area silicon photovoltaic cells for detection of the scatter and specular light from the sample. The thin cell profile permits placement of the scatter detector closer to the sample port for minimal scatter obscuration. The large cell area accepts the blur circle from an inexpensive molded acrylic dome for scatter collection. A dedicated pocket computer and printer calculates, displays and prints sample RMS roughness, average, and standard de-viation for multiple measurements; it also controls laser user-access, prints a tutorial, and identifies sample, operator and date/time. The laser is a 2mW HeNe (633 nm); safety issues are addressed. The specular beam reflects off the specular detector and onto an alignment target screen, ensuring sample alignment and measurement repeatability. The inverted design provides a gravity-loading sample stage that is completely accessible; custom sample mounts are readily added. Component sources are provided. Performance and correlation to other scatterometer and roughness measurement techniques such as optical and mechanical profilers are presented.

Photon Tunneling Microscopy

An evanescent field arising from photons tunneling through a total internal reflection boundary is employed as a high vertical resolution (less than 1 nm, detector-limited) height transducer which maps sample microtopography into a grayscale imagespace. A video densitometer and xyz oscilloscope restore the grayscale image to a 3D topographic image; restoration and viewing perspective manipulation are real-time. Depth of field is about 1 µm and lateral resolution is typical to an oil immersion microscope (about 0.4 µm).

Near-field optical recording without low-flying heads: Integral near-field optical (INFO) media

The promise of near-field (NF) optics to increase the density in optical data storage, whether solid immersion lenses (SILs), apertures, or their variants, has not yet been fulfilled, largely because of the difficulties with the head-media interface at near-field dimensions, especially if removable media is a design goal. We introduce a new approach to NF optical storage, in which integral near-field optics (INFO), in the form of nano-cylinders, are formed in the media upon manufacture. Combining the advantages of near- and far-field optical data storage, we obtain double the track density of digital versatile discs (DVD) in removable rewritable (RW) phase change media. Potential for in-track density increase is also demonstrated. We briefly report on the modeling, manufacture, and performance of INFO media.

High beam quality of ultraviolet radiation generated through resonant enhanced frequency doubling of a diode laser

The infrared emission from an external-cavity-tapered diode laser is frequency doubled in a 5-mm β-BaB2O4 crystal that is placed in a resonant-enhancement cavity. For a coupled diode power of 535 mW, 100 mW of continuous-wave, second-harmonic power is generated at λ=392 nm. The ultraviolet (UV) beam is measured to have a nearly ideal beam-quality parameter, M2≃1, in both meridians even though substantial double refraction is present in the nonlinear crystal. Printing of an array of submicron dots on a phase-change film is demonstrated with this UV beam. Also, by printing on photochemical film we demonstrate that improved film sensitivity is possible when a UV source is used.

Photon tunneling microscopy of diamond-turned surfaces.

The photon tunneling microscopes high-resolution, large-field, and real-time three-dimensional display with profilometry and continuously variable perspective make it a powerful tool for analysis of diamond-turned surfaces.

Embedded nano-optic media for near-field high-density optical data storage: modeling, fabrication, and performance

The promise of near-field (NF) optics to increase the density in optical data storage, whether solid immersion lenses (SILs), apertures, or their variants, has not yet been fulfilled, largely because of the difficulties with the head-media interface at near-field dimensions, especially if a design goal is removable media. We introduce a new approach to NF optical storage, in which the near-field elements, in the form of cylindrical NF nano-optics (nOptics), are integral with the media. Combining the advantages of near- and far-field optical data storage, we obtain double the track density of DVD in removable rewritable phase change media. Potential for in-track density increase is also demonstrated. We briefly report on the modeling, manufacture, and performance of NF nOptic media.

Super‐resolution through illumination by diffraction‐born evanescent waves

A diffraction grating in silicon with 50 nm lines and spaces is illuminated with diffraction‐born evanescent waves from its transparent replica. A rotation φ between the gratings results in a set of fringes with period λf that is larger than the period of the original gratings by a magnification factor M. These fringes are induced and observed with a photon tunneling microscope having an incident illumination of 650 nm in air. This super‐resolution by what may be considered a form of optical heterodyning with evanescent waves is discussed.

Immersion microscope for static testing of near-field phase-change optical disks

A modified optical microscope consisting of an oil immersion objective, index-matching fluid, transducer material, laser diode source, and photomultiplier tube is used to perform static testing of phase-change optical disks designed for use with nearfield optics. A 780-nm wavelength laser beam is coupled to the microscope optical path for read, write, and erase pulsing of the media. The oil immersion objective has a numerical aperture of 1.25. The transducer serves two purposes. The oil is kept off the surface of the disk, and an air gap is formed between the transducer and the surface of the disk. Rewritable phase-change disks with a first surface sensitive layer of GeSbTe were tested with the oil immersion microscope. The relative change in reflectivity due to writing and erasing of amorphous marks between 200 nm and 500 nm in diameter is detected. This technique provides a simple method of investigating the performance of nearfield optical recording media.