The technique of laser speckle photography has been developed with the aim of measuring the strain field around the tip of a fast crack. An image processing system to allow automatic point-by-point analysis of a speckle photograph is described. The Young's fringes diffraction pattern, produced by directing a narrow laser beam through the photograph, is digitised and processed by computer. Two algorithms have been developed based on Fourier and Walsh spectral analysis. The system can measure speckle displacements with an accuracy of better than 0.1 μm. A new technique for measuring time-varying displacement fields by multiple exposure of a single photograph is presented. Results are shown from a five-exposure speckle photograph of a cantilever deformed under quasi-static conditions. Extension of the technique to dynamic problems requires a stroboscopic laser light source; one chapter deals with the development of a Q-switched ruby laser for this purpose. Modulation of the cavity losses with a Pockels cell at up to 1 MHz results in a train of short (~50 ns) light pulses at the modulation frequency. Results are presented from the analysis of speckle photographs of cracks in polymethylmethacrylate (PMMA) under quasi-static loading. Three different data analysis methods for estimating the stress intensity factor from the displacement field are proposed and evaluated. Preliminary results from dynamic crack propagation studies are described. The dynamic stress intensity factor is estimated from double exposure speckle photographs of fast cracks in PMMA, recorded with the ruby laser in double pulse mode. The application of the techniques of moire and high speed photography to the study of dynamic fracture is also discussed; results are presented from a sequence of moire photographs recorded at 5 x 10<SUP>5</SUP> frames s<SUP>-1</SUP> . Further topics covered in the dissertation include a theoretical analysis of viscoelastic losses as a function of crack velocity, and strain-to-failure measurements on plastic bonded explosives in the Brazilian test using laser speckle photography.

We have completed a search for low luminosity companions, including high mass brown dwarfs, to all M dwarfs known within eight parsecs of the sun, and north of -25°. We found six new companions orbiting the survey stars. The masses of the six new secondaries fall between 0.39 and 0.05 M(⊙). Three of the new companions, G208-44B, GL 623B and LHS 1047B, and one previously known secondary in the survey, Ross 614B, are brown dwarf candidates with masses ∼80 Jupiters (0.08 M(⊙)), the dividing line between stars and brown dwarfs. In addition, we provide infrared photometry at J, H and K for all 99 survey members, and spectral types on standard system for half. Analysis of the entire sample indicates that 50% of the stars in the more distant half of the survey volume remain undetected, as is supported by the steadily growing M dwarf census over the last 45 years. The binary fraction of M dwarfs, 30-40%, is lower than that of earlier type main sequence stars, and there are more companions to M dwarfs found between 1 and 10 AU than in any other decade interval. We find that the luminosity function of the lowest mass stars is flat or rising to the end of the main sequence, and that the mass function undoubtedly rises to the stellar/substellar break. We illustrate that the resolution of close binaries is crucial if accurate luminosity and mass functions are to be determined. Finally, we estimate 0.02 M(⊙)/pc³ to be the amount of mass contributed by M dwarfs to the galactic mass. Based upon new mass-luminosity relations developed at infrared wavelengths using a sample of stars with well-determined masses between 1.2 and 0.08 M(⊙), we are able to define empirically the end of the main sequence. We present absolute magnitudes, colors and spectral types for objects at the theoretical lowest stellar mass. Using these relations, we conclude that a few brown dwarfs may have already been discovered. (Abstract shortened with permission of author.)

Approved for public release; distribution is unlimited / An investigation into the behavior of aluminized solid propellant combustion in a two-dimensional windowed rocket motor was conducted using holographic techniques. Holograms were recorded in the motor port, aft of the propellant grain and at the entrance to the exhaust nozzle for two different propellant compositions at varying operating pressures. Quantitative particle size data for particles larger than 20 microns were obtained from the holograms. From these data, the mean diameters (D32) of the larger particles were calculated and utilized to compare what effects pressure, location in the motor and aluminum content had on the behavior of the aluminum/aluminum oxide particles. D 32 was found to decrease with increasing pressure, but was unaffected by variations in low values of propellant aluminum loading. D 32 at the grain exit was found to be significantly less than within the grain port. / http://archive.org/details/holographicinves00butl / Lieutenant, United States Navy

Thesis (Ph. D.)--Oregon Graduate Center, 1982.

Ph.D. / Applied Physics / Using the extended Huygens Fresnel principle, the effect of the atmospheric turbulence on the statistical properties of a polychromatic speckle field, generated by a diffuse target, is studied in detail. The results, substantiated by experimental data, indicate that the atmospheric perturbation increases the variance of the received intensity substantially and is sensitive to the wavelength, beam size and beam geometry. The results for the covariance of the received intensity, normalized to the variance, indicate that, at low turbulence levels, reduction in vacuum speckle contrast ratio (VSCR) also reduces the normalized covariance but, with further increase in the turbulence level, reduction in the vacuum speckle contrast ratio increases the normalized covariance. Also it is found that for small detector spacings, the normalized covariance remains approximately constant even with substantial increase in the turbulence level. By resolving the time delayed covariance of the received intensity (TDC), into coherent and incoherent terms, it is shown that for large time delays, the time delayed covariance is determined by the incoherent fluctuations and for poor vacuum speckle contrast ratio, the time delayed covariance is not very sensitive to the wind velocity. Finally it is shown that due to the atmospheric perturbation the probability density function of the received intensity changes from an M-distribution or a sum of exponential distributions in vacuum to a K-distribution or a weighted sum of K-distributions in the presence of the turbulent atmosphere.

A novel method to reduce speckle noise from a digital image is presented. Speckle noise is introduced once a coherent light source is used. In this paper, we use the Empirical Mode Decomposition(EMD) method to remove speckles caused by such kind of coherent illumination. Many filter algorithms, such as Band-pass Filter, Enhanced Frost Filter, Gamma Filter, Enhanced Lee Filter, have been extensively studied to remove the speckle. However, they cannot remove noise effectively. The EMD method is able to analysis noise efficiently. This makes it possible to accurately analyze fringes in the frequency domain and to accurately retrieve the signal.

Phase-extraction from fringe patterns is an inevitable procedure in many applications, such as interferometry,Moiré analysis, and profilometry using structured light illumination. However, speckle noises could be introduced when a coherent light source is used. In this thesis, we use the empirical mode decomposition (EMD) to perform the speckle-reduction. It is found that phases can be extracted with high accuracy once speckle-reduction is performed with the EMD.

Thesis (M.S.)--Rochester Institute of Technology, 1992. / Typescript. Includes bibliographical references (leaves 110-114).

Thesis (M.S.)--Rochester Institute of Technology, 1990. / Typescript. Includes bibliographical references (leaves 48-50).

Orientador: Inacio Maria Dal Fabbro / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Agricola / Made available in DSpace on 2018-07-26T04:27:17Z (GMT). No. of bitstreams: 1 Rabelo_GiovaniFrancisco_D.pdf: 6243808 bytes, checksum: 89417cff3d167d53afb020241e6eb9c1 (MD5) Previous issue date: 2000 / Doutorado