Barry E. Paton

Nonlinear guided waves coupled nonlinearly in a planar GaAs/GaAlAs multiple quantum well structure

A nonlinear guided‐wave concept and nonlinear coupled‐wave equations are used to study numerically the coupling characteristics of two planar waveguides in a GaAs/GaAlAs multiple quantum well structure with self‐defocusing nonlinearities. Both the mode‐intensity‐dependent critical power and the coupling length are calculated for the first time using the nonlinear field distributions. An optically controlled modulation/switching behavior is predicted.

Red cell flux during the cardiac cycle in the rabbit myocardial microcirculation.

OBJECTIVE (1) To measure regional phasic myocardial red cell flux during a cardiac cycle using a laser Doppler velocimeter. (2) To test the responses of regional red cell flux to a vasodilator (adenosine), a vasoconstrictor (angiotensin II), and an inotrope (isoproterenol). METHODS Using an anaesthetised open-chest rabbit with the pericardium intact a 140-micron-tip fibre optic probe was placed in the left ventricular myocardium in various locations. With the fibre in place drugs were given to alter myocardial loading conditions while red cell flux was registered. RESULTS Phasic red cell flux was similar in the epicardium to endocardium giving an average endo/epi ratio of 1.14 in the rabbit heart. At least two peaks of increased red cell flux within a single cardiac cycle were observed. Some unique patterns for red cell flux were observed in specialised myocardial structures. Adenosine increased red cell flux but minimally changed the pattern of phasic flux throughout the cycle. CONCLUSIONS Laser Doppler velocimetry permits the recording of phasic red cell flux during the cardiac cycle in the myocardial microcirculation. Its pattern is determined by both coronary arterial inflow and venous outflow. The pattern of red cell flux may be characteristic for a region-probably determined by difference in tissue pressure (attributable to the pattern of muscle fibre shortening and collagen tethering) and changes in capillary length and density.

Multiple quantum well coupling element with losses

A nonlinear directional coupling element consisting of a GaAs‐based multiple quantum well (MQW) heterostructure sandwiched between two slab optical waveguides is analyzed numerically with optical absorption losses in the MQW included. Optical waveguides are designed to be made of lossless AlGaAs slabs of an appropriate composition corresponding to the wavelength of operation. Calculations indicate an improvement in the element’s overall propagation attenuation by about two orders of magnitude when compared to previous results dealing directly with MQW optical waveguides. Promising element performance characteristics are reported.

Microanalysis of dental caries using laser-scanned fluorescence

It is well known that enamel and dentin fluoresce when illuminated by short-wavelength optical radiation. Fluorescence emission from carious and non-carious regions of teeth have been studied using a new experimental scanning technique for fluorescence analysis of dental sections. Scanning in 2 dimensions will allow surface maps of dental caries to be created. These surface images are then enhanced using the conventional and newer image processing techniques. Carious regions can be readily identified and contour maps can be used to graphically display the degree of damage on both surfaces and transverse sections. Numerous studies have shown that carious fluorescence is significantly different than non-carious regions. The scanning laser fluorescence spectrometer focuses light from a 25 mW He-Cd laser at 442 nm through an objective lens onto a cross-section area as small as 3 micrometers in diameter. Microtome prepared dental samples 100 micrometers thick are laid flat onto an optical bench perpendicular to the incident beam. The sample is moved under computer control in X & Y with an absolute precision of 0.1 micrometers . The backscattered light is both spatial and wavelength filtered before being measured on a long wavelength sensitized photomultiplier tube. High precision analysis of dental samples allow detailed maps of carious regions to be determined. Successive images allow time studies of caries growth and even the potential for remineralization studies of decalcified regions.

Scanned laser-induced fluorescence reproducibility

Laser-induced fluorescence has potential for both caries research and diagnosis. However, research has shown that precise control is necessary for accurate enamel comparisons. Such factors as focus, number of sampling points, scan matrix size and reproducible placement of the scan matrix can all have substantial effects on results. Five noncarious third molars were mounted in acrylic and ground so that a flat Bu enamel surface was created. Each enamel area was covered with acid-resistant varnish except for a window approximately 1.0 mm2. Each specimen was mounted in the fluorometer for scanned laser fluorescence analysis using a 1.0 mm2 scan matrix. Readings were taken at 50 micrometers intervals for a total of 400 readings per matrix. Each specimen was remounted and reanalyzed in the fluorometer. Each specimen was lased (1.5 W, 1.5 mm f.s., 0.15 sec.) and reanalyzed as per above by fluorometer. Running-sums of line means were calculated for each scan and graphed. In all samples, the curves for nonlased enamel were lower and widely separated from those for lased enamel. In each specimen, the nonlased curves were either coincident or nearly so. The results indicate that ensuring constant focus, repeatable orientation of scan matrices and high sampling frequency collectively can lead to a high degree of scanned laser fluorescence reproducibility.

Measurement of subcutaneous adipose tissue blood flow in the morbidly obese using a laser Doppler velocimeter

Using a laser Doppler velocimeter (LDV) subcutaneous adipose tissue blood flow (AF) was recorded in the upright and supine positions in the upper and lower abdomen in 22 morbidly obese patients before gastroplasty. Age was 42 +/- 3 (mean +/- SEM), weight 135 +/- 7 kg, and body mass index (BMI) 51 +/- 3. Adipose flow expressed as mV was: supine, upper abdomen 647 +/- 23, lower abdomen 604 +/- 24; upright, upper abdomen 621 +/- 27, lower abdomen 607 +/- 29. AF was significantly more in the upper than lower abdomen (supine position) and AF was significantly lower in the lower abdomen upright than the upper abdomen supine. Regression analysis of age indicates that blood flow decreases in the lower abdomen so that in the supine position the difference between upper and lower abdomen AF increases. Similar analysis of BMI did not indicate significant trends. These data indicate that with morbid obesity there is lower tissue blood flow to the lower abdomen. This may explain why such patients may develop areas of painful ischemic necrosis in the dependent region of their anterior abdominal pannus.

Laser-scanned fluorescence of nonlased/normal, lased/normal, nonlased/carious, and lased/carious enamel

Research has shown that low levels of CO2 laser irradiation raise enamel resistance to sub-surface demineralization. Additionally, laser scanned fluorescence analysis of enamel, as well a laser and white light reflection studies, have potential for both clinical diagnosis and comparative research investigations of the caries process. This study was designed to compare laser fluorescence and laser/white light reflection of (1) non-lased/normal with lased/normal enamel and (2) non-lased/normal with non-lased/carious and lased/carious enamel. Specimens were buccal surfaces of extracted third molars, coated with acid resistant varnish except for either two or three 2.25 mm2 windows (two window specimens: non-lased/normal, lased/normal--three window specimens: non-lased/normal, non-lased carious, lased/carious). Teeth exhibiting carious windows were immersed in a demineralizing solution for twelve days. Non-carious windows were covered with wax during immersion. Following immersion, the wax was removed, and fluorescence and laser/white light reflection analyses were performed on all windows utilizing a custom scanning laser fluorescence spectrometer which focuses light from a 25 mWatt He-Cd laser at 442 nm through an objective lens onto a cross-section >= 3 (mu) in diameter. For laser/white light reflection analyses, reflected light intensities were measured. A HeNe laser was used for laser light reflection studies. Following analyses, the teeth are sectioned bucco-lingually into 80 micrometers sections, examined under polarized light microscopy, and the lesions photographed. This permits comparison between fluorescence/reflected light values and the visualized decalcification areas for each section, and thus comparisons between various enamel treatments and normal enamel. The enamel specimens are currently being analyzed.

Mask Making Using A Laser Writing System

An inexpensive IBM based laser writing system for making masks suitable for integrated optic applications is presented. The high degree of computer control makes this technique easy to use and relatively fast. The system can write lines, circles, arcs and shaded areas generating non-conventional designs and can be interfaced with various C A D programs.

Multiple-Quantum-Well Nonlinear Coupler

A nonlinear directional coupler, consisting of a GaAs-based Multiple Quantum Well structure sandwiched between two slab waveguides, is analysed.

Low- cost fiber optic sensing systems using spatial division multiplexing

It is shown how spatial division multiplexing (SDM) offers a low-cost solution to polling large numbers of passive optical sensors in large sensor arrays and also provides the possibility of low-cost fiber optic sensor systems. The geometric versatility of SDM allows optical multiplexing to be at the source, in the fiber distribution system, or at the detector. In most cases, electronic scanning can be driven from low-cost microcomputers. The simplicity of SDM promises reliable and maintainance-free operation.