One-dimensional collimation of laser array outputs

We consider a computer-generated hologram for the one-dimensional collimation in x of the output from a linear laser-diode array in y. Our concern is to produce one-dimensional pencil beams from each laser diode with small cross talk between the output from the separate laser diodes. Such outputs can be used in matrix-vector, neural net, and interconnection applications. The efficiency and the design of the computer-generated hologram are detailed, and initial optical laboratory results with an electron-beam recorded computer-generated hologram are presented.     

Thermal lensing in silver gallium selenide parametric oscillator crystals

We performed an experimental investigation of thermal lensing in silver gallium selenide (AgGaSe(2)) optical parametric oscillator crystals pumped by a 2-μm laser at ambient temperature. We determined an empirical expression for the effective thermal focusing power in terms of the pump power, beam diameter, crystal length, and absorption coefficient. This relation may be used to estimate average power limitations in designing AgGaSe(2) optical parametric oscillators. We also demonstrated an 18% slope efficiency from a 2-μm pumped AgGaSe(2) optical parametric oscillator operated at 77 K, at which temperature thermal lensing is substantially reduced because of an increase in the thermal conductivity and a decrease in the thermal index gradient dn/dT. Cryogenic cooling may provide an additional option for scaling up the average power capability of a 2-μm pumped AgGaSe(2) optical parametric oscillator.     

Unreacted cement content in macro-defect-free composites: impact on processing-structure-property relations

The effect of unreacted cement content on the processing, structure, and properties of macro-defect-free (MDF) composites fabricated from calcium aluminate cement (CAC), -alumina (Al₂O₃), and polyvinyl alcohol-acetate (PVAA) has been investigated. Three systems were formed with initial CAC: Al₂O₃ ratios of 5050, 3565, and 2575 by volume in their respective formulations. The amount of unreacted cement was reduced from 68.1 vol% which is present in standard (100% CAC) MDF cement, to 14.9 vol % for composites with an initial CAC: Al₂O₃ ratio of 2575, while the hydration product content was reduced from 18.1 vol % to 11.4 vol % for these respective systems. A hard core/soft shell continuum percolation model was used to determine that alumina substitution did not significantly affect the percolative nature of the interphase and bulk polymer regions. However, experiments showed that the reduction in unreacted cement content through Al₂O₃ substitution affected both the processing and microstructural features of these composites. The moisture absorption kinetics and flexural strength of composites exposed to 100% relative humidity were also evaluated, and it was found that their moisture sensitivity improved with decreasing unreacted cement content. A hypothesis is presented to explain the role of unreacted cement on the moisture sensitivity of these materials.     

Single-fibre polymer composites

We have used Raman spectroscopy to measure the axial stress distribution along a fibre during a quasi-static single fibre pull-out test. The stress distribution at the debonding front during the progress of debonding gives the maximum interfacial shear strength _s directly. In addition, the stress distribution along the fibre after debonding can be used to evaluate the interfacial normal stress and the frictional coefficient. For the plasma treated high modulus polyethylene (PE) fibres used here, _s is found to be 28 MPa by this method, while the apparent mean interfacial shear strength _a obtained from the regular single fibre pull-out test varies from 3 to 15 MPa with the fibre embedded length I _e. Stress distributions derived from the shear-lag theory fit the experimental data for fully bonded fibres well, giving values for the shear-lag constant K and the stress transfer length 1/ [1]. According to the shear-lag theory, _s = l _eacoth(l _e). If can be found for a given system from Raman spectroscopy, _s can be evaluated from the pull-out test using this equation.The regular pull-out tests, corrected for residual stress and interfacial friction, give the same _s but not the same or pull-out load as the slower Raman test. The shear-lag constant K can be expressed as a function of the matrix shear modulus and geometric terms. One of these terms is the effective interfacial radius, r _e, the radius at which the strain in the matrix equals the average matrix strain. Raman measurements indicate that r _e is small, only four times the fibre radius. This result is supported by polarizing optical microscopy. The model of Greszczuk [2], which assumes a uniform shear within an effective interaction thickness b _i, gives a similar result. We find that b _i = 20 m, about twice the fibre radius. Using the pull-out test data, as for other fibre composites, b _i and r _e predicted by shear-lag theories do not agree with the results of microscopy to this extent. In these cases _s is much larger than the yield strength of the matrix and as neither treatment considers plastic deformation of the matrix agreement should not be expected.     

The V-scope ultrasonic motion monitor: ergonomics applications in occupational manual materials handling and clinical exercise therapy

In this paper application is made of a three-dimensional telemetric ultrasound motion analysis technology originally designed for experimentation in the physics laboratory. When applied to human motion analysis in ergonomics, sports science and orthopaedic rehabilitation, this system offers great promise of solving problems hitherto insoluble or too costly to address.     

A composite cavity model for axisymmetric high Reynolds number separated flow II: Numerical analysis and results

In a companion paper (Wilmott and Fitt (1992)) a model was proposed for the separated high Reynolds number flow past a three-dimensional slender axisymmetric body. This composite model assumes that downstream of the body there is both a region of constant pressure and a Prandtl-Batchelor region. Matched asymptotic expansions were employed to recover a non-linear integro-differential equation for the shape of the separated region and some asymptotic solutions were obtained. The present study concerns the numerical solution of this equation and more detailed results concerning the cavity shape and closure properties.See also Journal of Engineering Mathematics 26: 539–555, 1992.     

Simultaneous daytime measurements of the atmospheric coherence diameter r(0) with three different methods

The most common parameter used in characterizing atmospheric turbulence (seeing) is the atmospheric coherence diameter, or r(0). r(0) can be measured in many ways. Three such techniques that are useful when one is making daytime seeing measurements by observing the Sun are described. Results from an experiment in which r(0) was measured with all three methods are presented.