Christopher C. Davis

Magnifying Superlens in the Visible Frequency Range

We demonstrate a magnifying superlens that can be integrated into a conventional far-field optical microscope. Our design is based on a multilayer photonic metamaterial consisting of alternating layers of positive and negative refractive index, as originally proposed by Narimanov and Engheta. We achieved a resolution on the order of 70 nanometers. The use of such a magnifying superlens should find numerous applications in imaging.

Lasers and Electro-Optics

1. Electromagnetic waves, light, and lasers 2. Optical frequency amplifiers 3. Introduction to two practical laser systems 4. Optical resonators containing amplifying media 5. Laser radiation 6. Control of laser oscillators 7. Optically pumped solid-state lasers 8. Gas lasers 9. Molecular gas lasers I 10. Molecular gas lasers II 11. Tunable lasers 12. Semiconductor lasers 13. Passive optical systems 14. Periodic optical systems, resonators and inhomogenous media 15. Optics of Gaussian beams 16. Optical fibers and waveguides 17. Optics of anisotropic media 18. The electro-optic and acousto-optic effects and modulation of light beams 19. Introduction to nonlinear processes 20. Wave propagation in nonlinear media 21. Detection of optical radiation 22. Coherence theory 23. Laser applications Index.

Far-field optical microscope with a nanometer-scale resolution based on the in-plane image magnification by surface plasmon polaritons

A new far-field optical microscopy technique capable of reaching nanometer-scale resolution has been developed recently using the in-plane image magnification by surface plasmon polaritons. This microscopy is based on the optical properties of a metal-dielectric interface that may, in principle, provide extremely large values of the effective refractive index neff up to 10-10 as seen by the surface plasmons. Thus, the theoretical diffraction limit on resolution becomes λ /2neff , and falls into the nanometer-scale range. The experimental realization of the microscope has demonstrated the optical resolution better than 50 nm for 502 nm illumination wavelength. However, the theory of such surface plasmon-based far-field microscope presented so far gives an oversimplified picture of its operation. For example, the imaginary part of the metal’s dielectric constant severely limits the surface-plasmon propagation and the shortest attainable wavelength in most cases, which in turn limits the microscope magnification. Here I describe how this limitation has been overcome in the experiment, and analyze the practical limits on the surface plasmon microscope resolution. In addition, I present more experimental results, which strongly support the conclusion of extremely high spatial resolution of the surface plasmon microscope.

Microwave dielectric characterization of binary mixtures of water, methanol, and ethanol

The complex dielectric constants of binary mixtures of water–methanol and water–ethanol in the frequency range from 45 MHz to 26.5 GHz, and binary mixtures of methanol–ethanol in the range from 200 MHz to 26.5 GHz have been measured with various volume fractions around room temperature by means of an open‐ended coaxial sensor and a network analyzer. Methanol–ethanol mixtures display a near‐Debye dispersion while water–alcohol mixtures show a Cole–Davidson dispersion. The logarithm of relaxation time log τ  and dielectric decrement Δe for methanol–ethanol mixtures show a good linear relation with the volume fraction of methanol, while log τ and Δe extracted with the Debye function for water–alcohol mixtures display a near‐linear relation with volume fraction of water. Two simple formulas are proposed for identifying the volume fractions of the components in binary mixtures of alcohol–alcohol and water–alcohol from a knowledge of τ and Δe for the pure liquids and the mixtures. The validity of these formulas has been demonstrated with three blind tests. The relation between the mole fraction of water and log τ for water–methanol and water–ethanol mixtures extracted by the use of a Cole–Davidson function clearly shows two linear regions, which implies a change of relaxation mechanism with mole fraction.

A review of communication-oriented optical wireless systems

This article presents an overview of optical wireless (OW) communication systems that operate both in the short- (personal and indoor systems) and the long-range (outdoor and hybrid) regimes. Each of these areas is discussed in terms of (a) key requirements, (b) their application framework, (c) major impairments and applicable mitigation techniques, and (d) current and/or future trends. Personal communication systems are discussed within the context of point-to-point ultra-high speed data transfer. The most relevant application framework and related standards are presented, including the next generation Giga-IR standard that extends personal communication speeds to over 1 Gb/s. As far as indoor systems are concerned, emphasis is given on modeling the dispersive nature of indoor OW channels, on the limitations that dispersion imposes on user mobility and dispersion mitigation techniques. Visible light communication systems, which provide both illumination and communication over visible or hybrid visible/infrared LEDs, are presented as the most important representative of future indoor OW systems. The discussion on outdoor systems focuses on the impact of atmospheric effects on the optical channel and associated mitigation techniques that extend the realizable link lengths and transfer rates. Currently, outdoor OW is commercially available at 10 Gb/s Ethernet speeds for Metro networks and Local-Area-Network interconnections and speeds are expected to increase as faster and more reliable optical components become available. This article concludes with hybrid optical wireless/radio-frequency (OW/RF) systems that employ an additional RF link to improve the overall system reliability. Emphasis is given on cooperation techniques between the reliable RF subsystem and the broadband OW system.

Impedance spectroscopy of human erythrocytes: system calibration, and nonlinear modeling

The authors present an impedance measurement method, the cell embedding technique, for human erythrocytes, and an accurate calibration procedure for a four-electrode impedance measurement system that gives reliable results over a wide frequency range-1 Hz to 10 MHz. To achieve high sensitivity, the cells are embedded in the pores of a Nuclepore filter. The calibration procedure assumes that the measurement system is linear and require measurement of three reference impedances. The reliability of the procedure is demonstrated with various RC circuits. Its application to the bio-impedance measurement system eliminates a quasi-dispersion in the high-frequency range and increases the bandwidth at both the low- and high-frequency ends of the range by about a decade. The experimental data are fitted to, an equivalent circuit model of the impedance of the embedded cells. The impedance spectra display constant-phase-angle (CPA) characteristics, which are used to describe the AC response of the interface between the cell surface, and the external electrolyte solution. Such a CPA element may be related to fractal character of the interface.<<ETX>>

Phase fluctuation optical heterodyne spectroscopy of gases.

The theory underlying the use of the phase fluctuation optical heterodyne (PFLOH) technique in studies of molecular relaxation, thermal conduction, and extremely weak absorptions in the gas phase is presented. Several new solutions to the heat conduction equation, with and without mass diffusion, which are appropriate to pulsed, cw, and modulated-cw laser modulation of weakly absorbing gases, are presented. Experiments employing pulsed and modulated-cw excitation have borne out the essential predictions of the theory. PFLOH systems for use in a trace detection application have been built with a demonstrated sensitivity, in terms of measurable absorption by the trace material, below 10(-10) cm(-1).

NEAR-FIELD DIRECT-WRITE ULTRAVIOLET LITHOGRAPHY AND SHEAR FORCE MICROSCOPIC STUDIES OF THE LITHOGRAPHIC PROCESS

Direct‐write lithography on a 100 nm scale has been carried out using the near‐field optical interaction between an uncoated tapered fiber tip and a layer of photoresist. This allows both lithography and shear force microscopic examination of the surface, which reveals morphological changes in the photoresist before development.

Two-dimensional metamaterial structure exhibiting reduced visibility at 500 nm.

Metamaterials provide unprecedented freedom and flexibility in the creation of new structures, which control electromagnetic wave propagation in very unusual ways. Very recently various theoretical designs for an electromagnetic cloak were suggested and an experimental realization of a partial cloak operating in a two-dimensional cylindrical geometry were reported in the microwave frequency range. We report on an experimental two-dimensional reduced visibility structure that approximates the distribution of the radial component of the dielectric permittivity necessary to achieve nonmagnetic cloaking in the visible frequency range.

A phase-locked shear-force microscope for distance regulation in near-field optical microscopy

A nonoptical phase-locked shear-force microscope utilizing a quartz crystal tuning fork acting as a voltage-controlled oscillator in a phase-locked loop has been implemented. A tapered optical fiber is rigidly mounted on one of the prongs of the fork to serve as both a shear-force pickup and a near-field optical probe. The crystal is driven at its resonance frequency through positive feedback of the monitored current through the crystal. This signal is used as the voltage-controlled oscillator in a phase-locked loop. The scheme allows for scan speeds far beyond the Q-limited amplitude sensor bandwidth and exhibits excellent sensitivity for a high-Q resonator. Furthermore, given the small vibration amplitude of the tip ( 6 nm), it is unlikely that the tip is making direct contact with the sample surface as has been suggested for the optical shear-force detection scheme.