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The probability density function (PDF) for the combined impact of motion-induced pointing jitter and laser beam scintillationKonate, Souleymane 01 January 2004 (has links)
No description available.
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New mathematical model for the intensity of a laser beam propagating through turbulent mediaAl Habash, M. Ammar 01 January 1998 (has links)
No description available.
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Polarization Dependent Ablation of Diamond with Gaussian and Orbital Angular Momentum Laser BeamsAlameer, Maryam 19 November 2019 (has links)
The vectorial nature (polarization) of light plays a significant role in light-matter interaction
that leads to a variety of optical devices. The polarization property of light
has been exploited in imaging, metrology, data storage, optical communication and
also extended to biological studies. Most of the past studies fully explored and dealt
with the conventional polarization state of light that has spatially symmetric electrical
field geometry such as linear and circular polarization. Recently, researchers
have been attracted to light whose electric field vector varies in space, the so-called
optical vector vortex beam (VVB). Such light is expected to further enhance and
improve the efficiency of optical systems. For instance, a radially polarized light
under focusing condition is capable of a tighter focus more than the general optical
beams with a uniform polarization structure, which improves the resolution of the
imaging system [1].
Interaction of ultrafast laser pulses with matter leads to numerous applications
in material processing and biology for imaging and generation of microfluidic systems.
A femtosecond pulse, with very high intensities of (10^{12} - 10^{13} W/cm^2), has
the potential to trigger a phenomenon of optical breakdown at the surface and therefore
induce permanent material modification. With such high intensities and taking
into account the fact that most materials possess large bandgap, the interaction is
completely nonlinear in nature, and the target material can be modified locally upon the surface and even further in bulk. The phenomenon of optical breakdown can be
further investigated by studying the nonlinear absorption. Properties like very short
pulse duration and the high irradiance of ultrashort laser pulse lead to more precise
results during the laser ablation process over the long pulsed laser. The duration of
femtosecond laser pulse provides a high resolution for material processing because
of the significant low heat-affected zone (HAZ) beyond the desired interaction spot
generated upon irradiating the material. Under certain condition, the interaction
of intense ultrashort light pulses with the material gives rise to the generation of
periodic surface structures with a sub-micron periodicity, i.e., much smaller than the
laser wavelength. The self-oriented periodic surface structures generated by irradiating
the material with multiple femtosecond laser pulses results in improving the
functionality of the material's surface such as controlling wettability, improving thin
film adhesion, and minimizing friction losses in automobile engines, consequently,
influences positively on many implementations.
In this work, we introduced a new method to study complex polarization states
of light by imprinting them on a solid surface in the form of periodic nano-structures.
Micro/Nanostructuring of diamond by ultrafast pulses is of extreme importance because
of its potential applications in photonics and other related fields.
We investigated periodic surface structures usually known as laser-induced periodic surface
structures (LIPSS) formed by Gaussian beam as well as with structured light carrying
orbital angular momentum (OAM), generated by a birefringent optical device
called a q-plate (QP). We generated conventional nano-structures on diamond
surface using linearly and circularly polarized Gaussian lights at different number
of pulses and variable pulse energies. In addition, imprinting the complex polarization state of different orders of optical vector vortex beams on a solid surface was fulfilled in the form of periodic structures oriented parallel to the local electric field of optical light. We also produced a variety of unconventional surface structures by superimposing a Gaussian beam with a vector vortex beam or by superposition of different order vector vortex beams.
This thesis is divided into five chapters, giving a brief description about laser-matter
interaction, underlying the unique characterization of femtosecond laser over
the longer pulse laser and mechanisms of material ablation under the irradiation of
fs laser pulse. This chapter also presents some earlier studies reported in formation
of (LIPSS) fabricated on diamond with Gaussian. The second chapter explains the
properties of twisted light possessing orbital angular momentum in its wavefront, a
few techniques used for OAM generation including a full explanation of the q-plate
from the fabrication to the function of the q-plate, and the tool utilized to represent
the polarization state of light (SoP), a Poincar'e sphere. Finally, the experimental details and results are discussed in the third and fourth chapters, respectively,
following with a conclusion chapter that briefly summarizes the thesis and some
potential application of our findings.
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Analysis of Thick Laminated Composite Beams using Variational Asymptotic MethodAmeen, Maqsood Mohammed January 2016 (has links) (PDF)
An asymptotically-exact methodology is presented for obtaining the cross-sectional stiffness matrix of a pre-twisted, moderately-thick beam having rectangular cross sections and made of transversely isotropic material. The beam is modelled with-out assumptions from 3-D elasticity. The strain energy of the beam is computed making use of the constitutive law and the kinematical relations derived with the inclusion of geometrical nonlinearities and initial twist. Large displacements and rotations are allowed, but small strain is assumed. The Variational Asymptotic Method (VAM) is used to minimize the energy functional, thereby reducing the cross section to a point on the reference line with appropriate properties, yielding a 1-D constitutive law. In this method as applied herein, the 2-D cross-sectional analysis is performed asymptotically by taking advantage of a material small parameter and two geometric small parameters. 3-D strain components are derived using kinematics and arranged as orders of the small parameters. Warping functions are obtained by the minimisation of strain energy subject to certain set of constraints that renders the 1-D strain measures well-defined. Closed-form expressions are derived for the 3-D non-linear warping and stress fields. The model is capable of predicting interlaminar and transverse shear stresses accurately up to first order.
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The effects of partial prestressing on newly cast Haydite beamsRiddell, John DeWitt. January 1955 (has links)
Call number: LD2668 .T4 1955 R54 / Master of Science
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The structural behavior of higher strength concreteHiremagalur, Narayan Babu D. January 1985 (has links)
Call number: LD2668 .T4 1985 H57 / Master of Science
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Correlations between the standard and alternative definitions of the beam quality factorStrauss, Hencharl Johan 04 1900 (has links)
Thesis (MSc)--University of Stellenbosch, 2005. / ENGLISH ABSTRACT: The beam quality factor (M2) of a laser is important because it describes both the quality of a laser
beam as well as its propagation. Particular applications require that the beam radii (from which the
M2 factor is determined) be defined in a specific way. The International Standards Organisation
(ISO) recently standardised the theoretically correct, but practically difficult second moment
definition of the beam radius.
This thesis aims to establish correlations between the second moment definition and other more
practical definitions. Chapter 2 presents a systematic introduction of moment theory for general
beams. Beam centre and radius definitions as well as beam classification are derived by means of
second and mixed moments. In Chapter 3 simple laser beams are modelled by means of a resonator
approach. The infinite number of solutions of this model is called Gaussian solutions, which are
found to be different for rectangular and cylindrical symmetric resonators. The zero order solution
for both symmetries is identified as the ideal solution to which all others can be compared to for
quality determinations. Chapter 4 presents different beam scanning devices, beam radius definitions
and correlations between these definitions. The theoretical basis for a new correlation theory is also
given. Chapter 5 describes programs and computations used to verify existing correlation methods
and to calculate correlation factors for a newly proposed theory. Chapter 6 presents the results of the
computations for both circular and rectangular symmetric beams. The ISO’s correlation theories are
tested first. Newly proposed correlation functions between the second moment and alternative
definitions as well as theoretical error graphs are given for various beams. A novel method to
correlate several important beam subclasses is also presented. Chapter 7 describes the experimental
setup, automation software and post processing techniques that were used to characterise a modified
CO2 TEA laser. It is further shown how the theory developed in previous chapters could be applied
to the experimental data. Chapter 8 presents the experimental results of the beam characterisation
measurements performed on two different beams that emanated from the CO2 TEA laser. Existing
and newly developed correlation theories are applied to the experimental data and the corresponding
results are compared. In Chapter 9, conclusions and suggestions with respect to the initial aims
identified in the first chapter are made. Several suggestions for future work are also made. / AFRIKAANSE OPSOMMING: Die bundel kwalitietsfaktor (M2) is baie belangrik omdat dit beide die kwaliteit en
voortplanting van ‘n laser bundel beskryf. Bundel radiusse (waarvan die M2 faktor bepaal
word) word verskillend gedefinieer vir spesifike toepassings. Die teoreties korrekte, maar
minder praktiese tweede moment definisie is onlangs deur die Internasionale Standaard
Organisasie (ISO) gestandariseer.
Hierdie tesis se hoofdoel is om die tweede moment definisie en ander meer praktiese
definisies te korreleer. Hoofstuk 2 stel die moment teorie van bundels sistematies bekend.
Dit word gewys hoe die senter en radius van ‘n bundel deur tweede en gemengde
momente gedefinieer kan word. In Hoofstuk 3 word laser bundels gemodeleer deur
middel van resonator aanslag. Die oneindige aantal oplossings wat verkry word heet
Gaussiese oplossings en is verskillend vir reghoekige en silindriese simmetriese
resonators. Dit word gewys dat die ideale bundel, waarmee alle ander bundels vergelyk
word, die zero orde oplossing van beide simmetrieë is. Hoofstuk 4 stel verskillende
bundel skanderings apparaat, bundel radius definisies en korrelasies tussen die definisies
bekend. Die teoretiese basis vir ‘n nuwe korrelasie teorie word ook gegee. Hoofstuk 5
beskryf die rekenaarprogramme en berekeninge wat gebruik word om huidige korrelasie
teorie mee te toets asook om nuwes mee te skep. Hooftuk 6 gee die resultate van die
berekeninge van die rekenaarprogramme vir beide reghoekig en silindriese simmetrie.
Die ISO se korrelasies word eerste getoets voordat nuwe teorieë bekend gestel word. In
Hoofstuk 7 word die eksperimentele opstelling, outomisasie sagteware en postprosessering
tegnieke gewys wat gebruik was om ‘n aangepaste CO2 TEA laser te
karakteriseer. Verder word dit gewys hoe die teorie wat in voorafgaande hoofstukke
ontwikkel is op eksperimentele data toegepas kan word. Hoofstuk 8 gee die
eksperimentele resultate van die bundel karakterisering van twee verskillende bundels
vanaf die CO2 TEA laser. Bestaande en nuwe korrelasie metodes word gebruik om die
bundels te korreleer en die resultate van elke metode word dan met mekaar vergelyk. In
Hoostuk 9 word afleidings gemaak. Daar word ook voorstelle gemaak vir potensiële
toekomstige werk.
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Nonlinear behaviour of reinforced concrete coupling beams趙作周, Zhao, Zuozhou. January 2001 (has links)
published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy
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Inelastic deformation of prestressed concrete beams劉彥良, Lau, Yin-lang, Clement. January 1969 (has links)
published_or_final_version / Civil Engineering / Master / Master of Science in Engineering
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Effects of repetitive loading on prestressed concrete beams with unbonded tendonsYim, Chun-nam, 嚴鎮南 January 1972 (has links)
published_or_final_version / Civil Engineering / Master / Master of Philosophy
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