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This paper reports on a detailed study that sought to establish an understanding of the molecular orientation of self-assembled monolayers (SAMs) formed from n-alkanethiols on obliquely deposited gold films. This study focuses on the azimuthal symmetry of the resonance signal obtained by rotation of the substrate about its normal. The important aspect of this work is to account for the anisotropic sum-frequency signal generated by gold and the preferred in- and out-of-plane orientations of the vibrational stretches. more...

The dielectric properties are reported for nanoporous thin films of poly(methyl silsesquioxane) (MSSQ) for use as an ultralow, dielectric intermetal insulator. Direct experimental conformation is provided that the films have low dielectric constants with low loss up to 10 GHz. Low-frequency measurements are also reported. more...

We have developed an experimental technique for corona poling a nonlinear polymer thin film for use in electro‐optic modulators. This method eliminates the pinhole and surface roughness damage that has been observed when corona poling a nonlinear polymer deposited on a conducting substrate. Electro‐optic modulators have been constructed to compare this corona poling technique to the contact poling technique commonly used with electro‐optic devices. Experimental results are presented that demonstrate that the corona poled electro‐optic devices were poled with electric fields near the dielectric breakdown of the thin polymer films—fields that are often difficult to achieve with contact poling. more...

Minimizing pulse-spreading caused by group velocity mismatch demands structures that achieve large conversion efficiency with a short interaction length. Optimized femtosecond-pulse generation in quasi-phase-matched thin-film structures will be discussed. > more...

We discuss the molecular engineering of a second order nonlinear optical (NLO) polymer materials specifically for ultrashort optical pulse diagnostics. We use second harmonic generation (SHG) frequency resolved optical gating (FROG) to measure the amplitude and phase of an ultrashort pulse. It is shown that thin poled TCV/PMMA are sufficiently nonlinear and robust to be used in Ti:Sapphire ultrashort pulse diagnostics. Since such thin NLO films are not limited by phasematching they hold great promise for extremely short pulse diagnostics. more...

Summary form only given. The distortion of an ultrashort pulse from propagation in a linear dispersive medium is well-understood. Not so understood are the distortions which occur when ultrashort optical pulses are generated in the dispersive medium by a nonlinear interaction. This talk will focus on second harmonic generation (SHG), where it is well-known that the second-harmonic (SH) pulse shape differs from the fundamental even for long pulses. This talk will focus on additional pulse distortions important when undistorted ultrashort pulses must be generated as efficiently as possible. more...

An in-line fiber modulator is an asymmetric directional coupler consisting of a continuous single mode fiber interacting through the evanescent fields with an electro-optic (EO) waveguide. Such an asymmetric coupler can be described by coupled wave theory. more...

A radio frequency (RF) modulated optical fiber link is an attractive alternative to coaxial cables to distribute large bandwidth analog RF signals. A critical component necessary for applications such as antenna remoting is a fiber optic modulator with a large dynamic range. The dominant modulator in use today is the Mach-Zehnder which requires linearization schemes to achieve a large dynamic range. We present an alternative modulator configuration which can be tuned to an operating point where the second, third, and fourth order intermodulation products are minimized, thus yielding a large dynamic range without linearization schemes. This inline fiber modulator consists of an electro-optic (EO) waveguide deposited directly onto single mode fiber half coupler block. more...

We highlight the unique attributes of sum-frequency spectroscopy by reviewing two case studies performed in our laboratory to investigate the orientation of macromolecules at interfaces. The first case study illustrates how spectral information of sum-frequency spectroscopy can be used to probe the orientation of monolayers and also independently probe the anisotropy of a metal interface, which influences the orientation of the monolayers, buried below a monolayer. The second case study illustrates how sum-frequency spectroscopy can be used to obtain spatial information of the uniformity of distribution and the density of coverage of synthetic proteins that are deposited as thin films. more...

Gynecologists frequently manage women with acute or chronic pain in the right iliac fossa. Appendicitis is one of the common conditions encountered in this setting. From the gynecologic perspective, issues regarding the role of laparoscopic appendectomy include radioimaging and laparoscopic diagnosis, operative technique, advantages and disadvantages, and laparoscopic appendectomy in pregnancy and in complicated appendicitis. Most studies are in favor of the procedure, and it seems reasonable to include it in training programs in gynecology. more...

A technique based on photothermal deflection spectroscopy has been developed for measuring the absolute absorption of polymers. The technique utilizes the frequency dependence measurement of the deflection signals to retrieve polymers' thermal properties and experimental parameters that are necessary to convert the deflection signals to the absolute absorption coefficients. All the measurements are done on the same experimental setup and the same sample without the need of obtaining either the materials' thermal properties or the reference absorption coefficients from other sources. This technique has been applied to several polymers and the results are reported. more...

Using a combination of positron annihilation and x-ray-diffraction techniques, we have shown that low hydrogen concentration hot wire chemical vapor deposition grown $a\ensuremath{-}\mathrm{S}\mathrm{i}:\mathrm{H}$ forms a continuous random network with no detectable free volume in the form of microvoids, and no evidence of a microcrystalline phase. On annealing up to 400 \ifmmode^\circ\else\textdegree\fi{}C, the amorphous network is seen to relax and the first stages of recrystallization occur. There is also evidence of vacancy clustering to form a low concentration of microvoids. The structural relaxation has a very low activation energy, around 0.1 eV, and is probably caused by a reconfiguration of hydrogen-terminated dangling, bond defects. The formation of microvoids and the recrystallization can both be interpreted by the migration of unterminated dangling-bond defects. more...

Rainfall records for three rain gauges on the farm Limerick and three rain gauges on the farm Mealielands were recorded from 1924 until 1999 by Mr DJ Irwin and his son Mr NG Irwin. The observations from these two nests of rain gauges are used to analyse the trends in rainfall measurements over time and to analyse the correlation of rainfall measurements between these rain gauges. The results presented in this report highlight the fact that the observations of rainfall are different to one another in many cases, indicating that care should be taken when selecting a rain gauge to represent the rainfall over a particular area. Analysis of the annual totals of rainfall has also found that at least 15 years of observations are required to determine a representative MAP value. The analysis of the monthly rainfall data also indicates that the rainy season commences in November and ends towards the end of April. A study of the extreme daily rainfall events shows that many of the storms are localised and are confined to an area around the rain gauges. The length of the droughts on these two farms are not as long as the national figures which would indicate that more point rainfall estimates are required to understand fully the spatial extent of a drought. WaterSA Vol.27(4) 2001: 559-564 more...

A Newton-Raphson complex root-finding algorithm, based on the thin-film transfer matrix analysis, is described. This second-order convergent algorithm, which requires only O(n) calculations per iteration, was presented to find the complex propagation constants of any mode in an n-layer planar waveguide. The number of calculations per iteration is reduced below those required by competitive schemes through application of the Cauchy-Riemann relations. The method demonstrates higher accuracy and improved efficiency over other iterative techniques, making this approach highly suitable for the analysis and design of planar structures consisting of a large number of layers. > more...

We demonstrate a GaAs/AlGaAs multiple-quantum-well in-line fiber optic intensity modulator. Based on evanescent wave coupling between a GaAs/AlGaAs anti-resonant reflective optical waveguide and a side-polished single mode fiber, this device concept combines the inherent advantages of in- line fiber devices with high-performance GaAs integrated optoelectronics. The GaAs waveguide utilizes distributed Bragg reflector mirrors, which are designed to provide maximum reflection at a given more angle, to phase-match to the low-index fiber. Intensity modulation of the transmitted light through the fiber is achieved by changing the complex propagation constant of the GaAs waveguide through the quantum-confined Stark effect. Typical device shows an on/off ratio of 4:1, with an applied voltage of 9V. Calculations show that with a longer interaction region, an on/off ratio of more than 40dB is achievable with the same applied voltage.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only. more...

Following heat treatments of Pt encapsulated Ni80Cr20 thin films on silicon substrates at temperatures ranging from 300 to 500 °C, it has been discovered that Cr atoms segregate at the original NiCr/Si interface to form an amorphous layer, while Ni atoms diffuse into the Si to form Ni silicide. The Cr‐rich amorphous layer acts as a ‘‘semipermeable membrane’’ which selectively passes Ni to form a very uniform NiSi layer. more...

A convenient synthesis of MMI (MIBI) and its ethyl analogue EMI was developed. A reliable 99mTc labelling method and easy formulation of these isonitriles are also described. HPLC and ITLC methods indicated acceptable radiochemical purity and stability over 3 h. more...

The weak absorption of waveguide materials can be measured by Photothermal Deflection Spectroscopy (PDS) with two orders of magnitude or higher sensitivity than conventional UV-VIS absorption spectroscopy. While it is easy to obtain relative absorption spectra for thin polymer films with PDS, extracting absolute absorption coefficients is more involved. The PDS measured signals depend on both thermal and optical absorption properties of materials. Knowledge of thermal properties is necessary to extract absorption coefficients. We report a methodology to obtain from PDS independently the thermal properties and absolute absorption coefficients. more...

A GaAs/AlGaAs in-line fiber optic filter for wavelength division multiplexing applications is demonstrated. The device consists of a GaAs/AlGaAs anti-resonant reflecting optical waveguide (ARROW) evanescently coupled to a single mode fiber. At certain discrete wavelengths, light is coupled from the fiber to the ARROW, due to phasematching conditions. Sharp resonances are observed around the design wavelength of 830 nm. The 3 dB cutoff bandwidth for TE polarization is 0.5 nm and the rejection ratio is 9 dB. more...

High-frequency instrumentation was acquired to perform: (a) high-frequency dielectric measurements on poled electro-active polymers and to determine the stability when exposed to microwave radiation, and (b) electro-optic measurements of the resonant enhancement of nonlinear polymers with demonstrated photochemical stability. In particular, the equipment was used to investigate large-bandwidth, traveling wave polymeric in-line fiber (PILF) modulator that is being co-developed by UC Davis and Optivision. This PILF amplitude modulator consists of a fiber half-coupler substrate evanescently coupled to a multimode electro-optic waveguide. PILF modulators are intrinsically rugged, exhibit low third order intermodulation nonlinearity and can be produced at lower cost than fiber pigtailed modulators. The equipment consisted of a high-frequency probe station, high-frequency amplifier and signal generator, 15 GHz photodetector, low relative intensity noise fiber coupled 1330 nm laser, and a 1064 diode pumped laser. The deviations from the original budget are that the $30K in UC cost sharing was used towards a laser ablation accessory for the probe station (instead of the thermal evaporator), the elimination of the 1550 nm laser source and the purchase with fund remaining a high-frequency signal generator. more...

Summary form only given. We have demonstrated an inline fiber optic filter using a GaAs ARROW waveguide as the overlay. It has a rejection ratio of 11 dB and a bandwidth of 7 nm. The inclusion of quantum wells in the waveguide core will lead to a new class of integrated fiber devices, including modulators, detectors, amplifiers, and lasers. more...

We are developing a traveling electro-optic modulator for analog microwave modulated fiber optic links used in radar applications. The modulator is a polymer in-line fiber device that has a rugged and low loss interface to single mode fibers and can be engineered to provide linear modulation over a large dynamic range. In the development of the modulator we take advantage of a variety properties available in polymers. The ability to deposit a conformal electro-optic thin film is used to fill the gaps between high-frequency co-planar electrodes and thus obtain a good overlap between the electric field produced by the the microwave electrodes and the fields in the optical fiber and the electro-optic waveguide. Reactive ion etching of the electro-optic polymer is used to trim the thickness of the polymer waveguide to obtain operation at a specific wavelength. The thermo-optic effect is used to fine tune the operation point of the modulator to obtain a large dynamic range. The geometry of the modulator permits operation close to the absorption peak of the electro-optic polymer and this provides the opportunity to take advantage of the resonant enhancement of the nonlinearity in the vicinity of an absorption band. more...

We review our recent research in the field of photochromic polymeric structures for optical data storage and nonlinear optics. We unity some of the sub-themes of azopolymer structures in the light of photo-induced movement of azobenzene molecules. In particular, we discuss photo-induced effects in supramolecular assemblies containing azobenzene molecules (e.g. Langmuir-Blodgett-Kuhn structures and ultrathin silane layers). Reorientation of azobenzenes in these structures will be compared to that observed in spin-cast films. Photoisomerization and photo-induced orientation of azobenzene molecules is also studied at the molecular level by means of azosilane molecules chemisorbed on Silicon Oxide substrates. We establish a correlation between polymer architecture and sub-glass transition temperature (Tg) light-induced molecular movement in high Tg nonlinear optical azo-polyimide polymers. We show that the isomerization reaction itself depends on the polymer molecular structure, and we present evidence of light-induced molecular movement 325 °C below Tg of a rigid NLO azo-polyimide polymer containing no flexible connector or tether. more...

A micromachined optical 'trap' to capture and move micron sized dielectric particles is presented. The trap consists of four single mode optical fibers mutually aligned to have a common optical beam intersection at the center of a micromachined housing. The intersection of the beams forms an optical 'cross-hair' which captures dielectric microparticles with a strong optical gradient force field, and holds them for further manipulation, visualization, and/or analysis. The stability and magnitude of the trapping force fields are comparable to the single beam 'optical tweezers' technique, but are considerably more versatile. more...

Electro-optic (EO) properties of nonlinear optical polymers (NLPs), of key interest in any device application, are most widely measured with ellipsometric(1, 2) or interferometric methods.(3) The major drawbacks of these techniques are: a) with ellipsometry, the Pockels coefficients cannot be extracted independently, b) refractive indices must be obtained from other measurements, and c) these methods ignore multiple reflection effects in stratified samples. Waveguiding methods such as attenuated total reflection (ATR) measurements are capable of a complete linear optical and EO characterization of NLPs.(4) But the ATR prism complicates the angular scans, and waveguiding conditions over a large spectral range are difficult to fulfill with a single sample. more...

We use the technique of Frequency Resolved Optical Gating (FROG) [1] to measure the amplitude and phase of an ultrashort pulse.[2] Although there are several variations of the FROG technique which use different nonlinear processes, second harmonic generation (SHG) FROG is particularly well suited for measuring unamplified nJ pulses directly from a modelocked Ti:sapphire oscillator, since SHG produces a much larger signal than the higher order nonlinear processes. Experimentally, SHG FROG is similar to a second-order intensity autocorrelation, except that the second harmonic spectrum is measured as a function of time. more...

Summary form only given. We demonstrate the application of decal technique to electro-optic modulators. It allows the deposition of high-quality, corona-poled, nonlinear polymer films onto structures without subjecting them to spin coating, large electrostatic fields, and other nonlinear polymer processing steps that may damage the underlying device. Another distinct advantage of the decal deposition for devices where the film thickness determines the optical spatial resonances, such as Fabry Perot structures or waveguides, is that the thickness of the film is determined prior to deposition on the final substrate and since many identical patches are formed it ensures reproducibility between devices. The decal deposition technique significantly simplifies the fabrication of the in-line fiber electro-optic modulators. more...

Frequency Resolved Optical Gating (FROG) [1] is a newly-developed technique for determining both the amplitude and phase of an ultrashort pulse.[2] Although there are several variations of the FROG technique which use different nonlinear processes, second harmonic generation (SHG) FROG is particularly well suited for measuring un-amplified nJ pulses directly from a modelocked Ti:sapphire oscillator, since SHG produces a much larger signal than the higher order nonlinear processes. In order for SHG FROG to accurately characterize ultrashort pulses, care must be taken to insure the second harmonic signal is not distorted by the nonlinear material, in phase-matched frequency doubling crystals for example, the group velocity mismatch (GVM) can cause severe distortion of the generated pulses over long interaction lengths. Since this finite phase matching bandwidth becomes less of a problem as the crystal thickness is reduced, the thinnest possible crystals (≈ 50 μm) are generally used for ultrashort-pulse measurement applications.[3] However, even using such short crystals, the crystal has to be optimally oriented to achieve proper phasematching for a given center frequency. Furthermore, fabricating such phasematched, polished, ultra-thin crystals is extremely difficult. Thus, an ideal SHG material for short pulse diagnostics is one that can generate an adequate signal intensity while being thin enough to avoid pulse broadening and precise angle tuning. more...

Summary form only given. We have designed and fabricated a polymeric in-line fiber modulator using novel fabrication techniques. This device is based on evanescent coupling from a fiber half-coupler to a nonlinear polymer waveguide and takes advantage of a unique polymer deposition process. more...

A cross sectional TME study has been conducted into the structure and morphology of p- and i-type a-Si:H layers of device quality deposited on textured TCO on glass. The layer thickness over peaks is shown to be equivalent to that for flat regions, while defective regions are found in narrow valleys, initiating from the pit of the valleys. These regions may act as regions of excessive recombination and/or shunting regions, thus leading to a reduced Voc and fill factor in thin solar cells. A cosine relationship was found between the deposited thickness and the facet angles of the surface TCO crystals. It is concluded that for best performance of the deposited layer, the deposition has to be completely isotropie, and that the preferred surface morphology of textured TCO be sharp peaks with wider valleys. more...