White-light reconstruction setup for shearograms using optical-fiber waveguides

A white-light reconstruction setup for shearograms using optical-fiber waveguides is presented. The setup is compact, is not susceptible to dust and scratches, and enables the two-dimensional fringe pattern on shearograms to be viewed directly under uniform and enhanced illumination with minimal image distortion.     

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.     

Radioactive contamination of the environment with241Am as a result of the chernobyl accident

All Union Scientific-Research Institute of Nuclear Power Plants. Industrial Association "Chernobyk'skaya Atomnaya élektrostantsiya," Ukraine. Translated from Atomnaya énergiya, Vol. 77, No. 2, pp. 140–145, August, 1994.     

Thermodynamic magnetization discontinuity between the A and B phases of superfluid3he

We present data for the magnitude of the thermodynamic magnetization discontinuity at the equilibrium A-B transition in superfluid³He, M_AB, over its entire pressure-temperature-magnetic field phase diagram. The data was taken by measuring flux changes in a SQUID pick-up coil, which was calibrated by a novel first-principles technique. We compare our results with those of NMR experiments, and find that the two types of measurements yield different values, and this discrepancy is not the result of thermometry or field errors.     

Forward scattering of a Gaussian beam by a nonabsorbing sphere

The forward scattering of a Gaussian laser beam by a spherical particle located along the beam axis is analyzed with the generalized Lorenz-Mie theory (GLMT) and with diffraction theory. Forwardscattering and near-forward-scattering profiles from electrodynamically levitated droplets, 51.6 μm in diameter, are also presented and compared with GLMT-based predictions. The total intensity in the forward direction, formed by the superposition of the incident and the scattered fields, is found to correlate with the particle-extinction cross section, the particle diameter, and the beam width. Based on comparison with the GLMT, the diffraction solution is accurate when beam widths that are approximately greater than or equal to the particle diameter are considered and when large particles that have an extinction efficiency near the asymptotic value of 2 are considered. However, diffraction fails to describe the forward intensity for more tightly focused beams. The experimental observations, which are in good agreement with GLMT-based predictions, reveal that the total intensity profile about the forward direction is quite sensitive to particle axial position within a Gaussian beam. These finite beam effects are significant when the ratio of the beam to the particle diameter is less than approximately 5:1. For larger beam-to-particle-diameter ratios, the total field in the forward direction is dominated by the incident beam.     

Flat-field postobjective polygon scanner

A general two-dimensional ray-trace analysis is presented for the motion of a geometric focal point over a flat surface provided by a postobjective rotating polygon laser beam scanner. The exact defocus equation is derived for any value of the neutral scan position deflection angle and the polygon rotation angle. The scan nonlinearity is derived for the special case of a zero neutral scan deflection angle. Geometric parameters were found that reduce the peak-to-peak defocus by more than an order of magnitude from that found in previous design approaches. Conditions were also found that reduce scan nonlinearity to less than 2 × 10(-4). Practical limitations, such as large polygons and beam obscurations, encountered in the implementation of postobjective scanning are discussed.     

Generation of multifrequency laser emission quasi equally spaced throughout the entire visible region

A circularly polarized, monochromatic laser beam is focused into a Raman cell, which contains hydrogen to generate rotational stimulated Raman emission. After linear polarization, this two-color (separated by 587 cm(-1)) laser beam is focused several times into a second Raman cell that is filled with hydrogen to generate a multifrequency laser emission. Many rotational and vibrational lines are generated efficiently by this multipass effect. Eighteen colors that are quasi equally spaced with a rather flat intensity distribution are generated throughout the entire visible region. The present multifrequency laser emission may be advantageously used for illumination in a higher-grade display, such as a laser light show.     

Superresolution readout system with electrical equalization for optical disks

An electrical equalizer for a superresolution readout system with an optical apodizer is proposed and verified experimentally. This superresolution readout system uses a five-tap transversal filter as the electrical equalizer instead of additional optics to suppress enlarged sidelobes, and it achieves higher resolution than the diffraction-limited system. The transfer function of the electrical equalizer is also derived theoretically. This approach allows fabrication of a readout system with a good signal-to-noise ratio and a compact head.     

Detection of probe dither motion in near-field scanning optical microscopy

The probe-to-sample separation in near-field scanning optical microscopes can be regulated by a noncontact shear-force sensing technique. The technique requires the measurement of a minute dither motion applied to the probe. We have characterized an optical detection method for measuring this motion to determine the optimum detection configuration in terms of sensitivity and stability. A scalar diffraction model of the detection method is developed for calculating sensitivity, and experimental results are found to be in good agreement with the theoretical predictions. We find that maximum sensitivity and stability cannot be achieved simultaneously, and it may be desirable in practice to trade sensitivity for enhanced stability.