Dissertations / Theses on the topic 'Laser manipulation (Nuclear physics)'
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Chism, William Wesley. "Nonlinear classical dynamics in intense laser-atom physics /." Digital version accessible at:, 2000. http://wwwlib.umi.com/cr/utexas/main.
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Ganic, Djenan, and dga@rovsing dk. "Far-field and near-field optical trapping." Swinburne University of Technology. Centre for Micro-Photonics, 2005. http://adt.lib.swin.edu.au./public/adt-VSWT20051130.135436.
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Optical trapping techniques have become an important and irreplaceable tool in many research disciplines for reaching non-invasively into the microscopic world and to manipulate, cut, assemble and transform micro-objects with nanometer precision and sub-micrometer resolution. Further advances in optical trapping techniques promise to bridge the gap and bring together the macroscopic world and experimental techniques and applications of Microsystems in areas of physics, chemistry and biology.
In order to understand the optical trapping process and to improve and tailor experimental techniques and applications in a variety of scientific disciplines, an accurate knowledge of trapping forces exerted on particles and their dependency on environmental and morphological factors is of crucial importance. Furthermore, the recent trend in novel laser trapping experiments sees the use of complex laser beams in trapping arrangements for achieving more controllable laser trapping techniques. Focusing of such beams with a high numerical aperture (NA) objective required for efficient trapping leads to a complicated amplitude, phase and polarisation distributions of an electromagnetic field in the focal region. Current optical trapping models based on ray optics theory and the Gaussian beam approximation are inadequate to deal with such a focal complexity.
Novel applications of the laser trapping such as the particle-trapped scanning near field optical microscopy (SNOM) and optical-trap nanometry techniques are currently investigated largely in the experimental sense or with approximated theoretical models. These applications are implemented using the efficient laser trapping with high NA and evanescent wave illumination of the sample for high resolution sensing. The proper study of these novel laser trapping applications and the potential benefits of implementation of these applications with complex laser beams requires an exact physical model for the laser trapping process and a nanometric sensing model for detection of evanescent wave scattering.
This thesis is concerned with comprehensive and rigorous modelling and characterisation of the trapping process of spherical dielectric particles implemented using far-field and near-field optical trapping modalities. Two types of incident illuminations are considered, the plane wave illumination and the doughnut beam illumination of various topological charges. The doughnut beams represent one class of complex laser beams. However, our optical trapping model presented in this thesis is in no way restricted to this type of incident illumination, but is equally applicable to other types of complex laser beam illuminations. Furthermore, the thesis is concerned
with development of a physical model for nanometric sensing, which is of great importance for optical trapping systems that utilise evanescent field illumination for achieving high resolution position monitoring and imaging.
The nanometric sensing model, describing the conversion of evanescent photons into propagating photons, is realised using an analytical approach to evanescent wave scattering by a microscopic particle. The effects of an interface at which the evanescent wave is generated are included by considering the scattered
field reflection from the interface. Collection and imaging of the resultant scattered field by a high numerical aperture objective is described using vectorial diffraction theory. Using our sensing model, we have investigated the dependence of the scattering on the particle size and refractive index, the effects of the interface on the scattering cross-section, morphology dependent resonance effects associated with the scattering process, and the effects of the incident angle of a laser beam undergoing total internal reflection to generate an evanescent field. Furthermore, we have studied the detectability of the scattered signal using a wide area detector and a pinhole detector. A good agreement between our experimental measurements of the focal intensity distribution in the back focal region of the collecting objective and the theoretical predictions confirm the validity of our approach.
The optical trapping model is implemented using a rigorous vectorial diffraction theory for characterisation of the electromagnetic field distribution in the focal region of a high NA objective. It is an exact model capable of considering arbitrary amplitude, phase and polarisation of the incident laser beam as well as apodisation functions of the focusing objective. The interaction of a particle with the complex focused field is described by an extension of the classical plane wave Lorentz-Mie theory with the expansion of the incident field requiring numerical integration of finite surface integrals only. The net force exerted on the particle is then determined using the Maxwell stress tensor approach. Using the optical trapping model one can
consider the laser trapping process in the far-field of the focusing objective, also known as the far-field trapping, and the laser trapping achieved by focused evanescent field, i.e. near-field optical trapping.
Investigations of far-field laser trapping show that spherical aberration plays a significant role in the trapping process if a refractive index mismatch exists between the objective immersion and particle suspension media. An optical trap efficiency is severely degraded under the presence of spherical aberration. However, our study shows that the spherical aberration effect can be successfully dealt with using our optical trapping model. Theoretical investigations of the trapping process achieved using an obstructed laser beam indicate that the transverse trapping efficiency decreases rapidly with increasing size of the obstruction, unlike the trend predicted using a ray optics model. These theoretical investigations are in a good agreement with our experimentally observed results.
Far-field optical trapping with complex doughnut laser beams leads to reduced lifting force for small dielectric particles, compared with plane wave illumination, while for large particles it is relatively unchanged. A slight advantage of using a doughnut laser beam over plane wave illumination for far-field trapping of large dielectric particles manifests in a higher forward axial trapping efficiency, which increases for increasing doughnut beam topological charge. It is indicated that the maximal transverse trapping efficiency decreases for reducing particle size and that the rate of decrease is higher for doughnut beam illumination, compared with plane wave illumination, which has been confirmed by experimental measurements.
A near-field trapping modality is investigated by considering a central obstruction placed before the focusing objective so that the obstruction size corresponds to the minimum convergence angle larger than the critical angle. This implies that the portion of the incident wave that is passed through the high numerical aperture objective satisfies the total internal reflection condition at the surface of the coverslip, so that only a focused evanescent field is present in the particle suspension medium. Interaction of this focused near-field with a dielectric micro-particle is described and investigated using our optical trapping model with a central obstruction. Our investigation shows that the maximal backward axial trapping efficiency or the lifting
force is comparable to that achieved by the far-field trapping under similar conditions for either plane wave illumination or complex doughnut beam illumination. The dependence of the maximal axial trapping efficiency on the particle size is nearly linear for near-field trapping with focused evanescent wave illumination in the Mie size regime, unlike that achieved using the far-field trapping technique.
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Ganic, Djenan. "Far-field and near-field optical trapping." Australasian Digital Thesis Program, 2005. http://adt.lib.swin.edu.au/public/adt-VSWT20051130.135436.
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Thesis (PhD) - Swinburne University of Technology, Faculty of Engineering and Industrial Sciences, Centre for Micro-Photonics, 2005.A thesis submitted for the degree of Doctor of Philosophy, Centre for Micro-Photonics, Faculty of Engineering and Industrial Sciences, 2005. Typescript. Includes bibliographical references (p. 164-177). Also available on cd-rom.
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Summers, Michael David. "Optical micromanipulation of aerosols." Thesis, St Andrews, 2009. http://hdl.handle.net/10023/779.
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Burnham, Daniel Richard. "Microscopic applications of holographic beam shaping and studies of optically trapped aerosols /." St Andrews, 2009. http://hdl.handle.net/10023/699.
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Shane, Janelle. "Optical micromanipulation using dispersion-compensated and phase-shaped ultrashort pulsed lasers /." St Andrews, 2009. http://hdl.handle.net/10023/730.
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Little, Helen. "Optical micromanipulation using ultrashort pulsed laser sources." Thesis, St Andrews, 2007. http://hdl.handle.net/10023/338.
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Milne, Graham. "Optical sorting and manipulation of microscopic particles." Thesis, St Andrews, 2007. http://hdl.handle.net/10023/334.
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Morrish, Dru, and DruMorrish@gmail com. "Morphology dependent resonance of a microscope and its application in near-field scanning optical microscopy." Swinburne University of Technology. Centre for Micro-Photonics, 2005. http://adt.lib.swin.edu.au./public/adt-VSWT20051124.121838.
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In recent times, near-field optical microscopy has received increasing attention for its
ability to obtain high-resolution images beyond the diffraction limit. Near-field optical
microscopy is achieved via the positioning and manipulation of a probe on a scale less
than the wavelength of the incident light.
Despite many variations in the mechanical design of near-field optical microscopes almost all rely on direct mechanical access of a cantilever or a derivative form to probe the sample. This constricts the study to surface examinations in simple sample environments. Distance regulation between the sample surface and the delicate probe
requires its own feedback mechanism. Determination of feedback is achieved through
monitoring the shift of resonance of one arm of a 'tuning fork', which is caused by the interaction of the probes tip with the Van der Waals force. Van der Waals force emanates from atom-atom interaction at the top of the sample surface. Environmental contamination of the sample surface with additional molecules such as water makes accurate measurement of these forces particularly challenging. The near-field study of
living biological material is extremely difficult as an aqueous environment is required for its extended survival. Probe-sample interactions within an aqueous environment that
result in strong detectable signal is a challenging problem that receives considerable
attention and is a focus of this thesis.
In order to increase the detectible signal a localised field enhancement in the probing region is required. The excitation of an optically resonant probe by morphology dependent resonance (MDR) provides a strong localised field enhancement. Efficient MDR excitation requires important coupling conditions be met, of which the localisation of the incident excitation is a critical factor.
Evanescent coupling by frustrated total internal reflection to a MDR microcavity provides an ideal method for localised excitation. However it has severe drawbacks if the probe is to be manipulated in a scanning process. Tightly focusing the incident illumination by a high numerical aperture objective lens provides the degree of freedom to enable both MDR excitation and remote manipulation. Two-photon nonlinear excitation is shown to couple efficiently to MDR modes due to the high spatial localisation of the incident excitation in three-dimensions. The dependence of incident excitation localisation by high numerical aperture objective on MDR efficiency is thoroughly examined in this thesis. The excitation of MDR can be enhanced by up to 10 times with the localisation of the incident illumination from the centre of the
microcavity to its perimeter.
Illuminating through a high numerical aperture objective enables the remote noninvasive
manipulation of a microcavity probe by laser trapping. The transfer of photon momentum from the reflection and refraction of the trapping beam is sufficient enough to exert piconewtons of force on a trapped particle. This allows the particle to be held and scanned in a predictable fashion in all three-dimensions. Optical trapping
removes the need for invasive mechanical access to the sample surface and provides a means of remote distance regulation between the trapped probe and the sample. The femtosecond pulsed beam utilised in this thesis allows the simultaneous induction of two-photon excitation and laser trapping. It is found in this thesis that a MDR microcavity can be excited and translated in an efficient manner. The application of this technique to laser trapped near-field microscopy and single molecule detection is of particular interest.
Monitoring the response of the MDR signal as it is scanned over a sample object enables a near-field image to be built up. As the enhanced evanescent field from the propagation of MDR modes around a microcavity interacts with different parts of the sample, a measurable difference in energy leakage from the cavity modes occurs. The definitive spectral properties of MDR enables a multidimensional approach to imaging and sensing, a focus of this thesis. Examining the spectral modality of the MDR signal
can lead to a contrast enhancement in laser trapped imaging. Observing a single MDR mode during the scanning process can increase the image contrast by up to 1:23 times compared to that of the integrated MDR fluorescence spectrum.
The work presented in this thesis leads to the possibility of two-photon fluorescence
excitation of MDR in combination with laser trapping becoming a valuable tool in near-
field imaging, sensing and single molecule detection in vivo. It has been demonstrated
that particle scanned, two-photon fluorescence excitation of MDR, by laser trapping 'tweezers' can provide a contrast enhancement and multiple imaging modalities. The spectral imaging modality has particular benefits for image contrast enhancements.
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Li, Tao. "Manipulation of cold atoms using an optical one-way barrier." Thesis, Connect to title online (Scholars' Bank) Connect to title online (ProQuest), 2008. http://hdl.handle.net/1794/8589.
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Thesis (Ph. D.)--University of Oregon, 2008.Typescript. Includes vita and abstract. Includes bibliographical references (leaves 114-119). Also available online in Scholars' Bank; and in ProQuest, free to University of Oregon users.
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Morris, Jill E. "Studies of novel beam shapes and applications to optical manipulation." Thesis, University of St Andrews, 2010. http://hdl.handle.net/10023/1699.
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In this thesis an investigation into novel beams and optical manipulation is presented. Sculpting the phase profile of a Gaussian beam can result in the generation of a beam with unusual properties. Described in this thesis are optical vortices, Bessel beams and Airy beams. Additionally, optical manipulation was investigated using both novel beams and Gaussian beams with an emphasis on the use of a broad bandwidth laser source. The generation of multiple broadband optical trap sites was explored, and the transfer of orbital angular momentum from a broadband optical vortex to trapped microspheres was demonstrated. An introduction to the thesis and an overview of laser sources used for optical manipulation is presented in Chapters 1 and 2. Chapters 3 and 4 detail the background of optical manipulation and novel beam shaping. In Chapter 5, an investigation into the generation of multiple broadband optical trap sites is presented. Chapter 6 details the use of a ‘white light’ optical vortex to transfer orbital angular momentum to trapped microspheres. Chapter 7 presents the results of an investigation carried out using a supercontinuum source to characterise the wavelength and spatial coherence dependence of the properties of an optical Airy beam. The use of a monochromatic laser to generate Bessel beams that propagate along curved trajectories is detailed in Chapter 8. Chapter 9 summarises the thesis and suggests future work.
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Metzger, Nikolaus K. "Longitudinal optical binding." Thesis, St Andrews, 2008. http://hdl.handle.net/10023/519.
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Christandl, Katharina. "Advancing neutral atom quantum computing studies of one-dimensional and two-dimensional optical lattices on a chip /." Connect to resource, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1123263229.
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Thesis (Ph. D.)--Ohio State University, 2005.Title from first page of PDF file. Document formatted into pages; contains xxiii, 261 p.; also includes graphics. Includes bibliographical references (p. 256-261). Available online via OhioLINK's ETD Center
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Singh, Pooja. "Quantum Coherent Control and Propagation in Lambda System." Thesis, University of North Texas, 2016. https://digital.library.unt.edu/ark:/67531/metadc849750/.
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Strong coherence in quasi-resonant laser driven system interferes with effective relaxations, resulting in behaviors like, coherent population trapping and Electromagnetically induced transparency. The Raman system can optimize this utilizing excited coherence in the lambda system when exposed to counter- intuitive pump-stokes pulses. The phenomenon can result in complete population transfer between vibrational levels called Stimulated Raman adiabatic passage(STIRAP). STIRAP and CHIRAP have been studied with Gaussian and chirped pulses. The optical propagation effects in dense medium for these phenomenon is studied to calculate the limitations and induced coherences. Further, the effect of rotational levels has been investigated. The molecular vibrational coherence strongly depends on the effect of rotational levels. The change in coherence interaction for ro-vibrational levels are reported and explained. We have considered the effects on the phase of radiation related to rotational mechanical motion of quantum system by taking advantages in ultra strong dispersion medium provided by quantum coherence in lambda system. The enhanced Fizeau effect on a single atom is observed.
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Dienerowitz, Maria. "Plasmonic effects upon optical trapping of metal nanoparticles." Thesis, University of St Andrews, 2010. http://hdl.handle.net/10023/1634.
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Optical trapping of metal nanoparticles investigates phenomena at the interface of plasmonics and optical micromanipulation. This thesis combines ideas of optical properties of metals originating from solid state physics with force mechanism resulting from optical trapping. We explore the influence of the particle plasmon resonance of gold and silver nanospheres on their trapping properties. We aspire to predict the force mechanisms of resonant metal particles with sizes in the Mie regime, beyond the Rayleigh limit. Optical trapping of metal nanoparticles is still considered difficult, yet it provides an excellent tool to investigate their plasmonic properties away from any interface and offers opportunities to investigate interaction processes between light and nanoparticles. Due to their intrinsic plasmon resonance, metal nanoparticles show intriguing optical responses upon interaction with laser light. These differ greatly from the well-known bulk properties of the same material. A given metal nanoparticle may either be attracted or repelled by laser light, only depending on the wavelength of the latter. The optical forces acting on the particle depend directly on its polarisability and scattering cross section. These parameters vary drastically around the plasmon resonance and thus not only change the magnitude but also the direction and entire nature of the acting forces. We distinguish between red-detuned and blue-detuned trapping, that is using a trapping wavelength shorter or longer than the plasmon resonance of the particle. So far optical trapping of metal nanoparticles has focussed on a wavelength regime far from the particle’s resonance in the infrared. We experiment with laser wavelengths close to the plasmon resonance and expand the knowledge of metal nanoparticle trapping available to date. Existing theoretical models are put to the test when we compare these with our real experimental situations.
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Gherardi, David Mark. "Studies of particle and atom manipulation using free space light beams and photonic crystal fibres." Thesis, St Andrews, 2009. http://hdl.handle.net/10023/703.
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Sadeghi, Mohammad Mehdi 1959. "SYMBOLIC MANIPULATION IN REACTOR PHYSICS." Thesis, The University of Arizona, 1986. http://hdl.handle.net/10150/275520.
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Okoye, Raphael. "Manipulation of short pulses." Thesis, Stellenbosch : Stellenbosch University, 2013. http://hdl.handle.net/10019.1/85576.
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Thesis (MSc)--Stellenbosch University, 2013.ENGLISH ABSTRACT: An ultra-fast laser pulse can be described in the time or frequency domain. If the timebandwidth product of an ultra-fast pulse is not satisfied, then the pulse is stretched. Stretching can be described in the time or frequency domain. In the time domain, it is called a chirp and in the frequency domain, it is known as the group delay dispersion GDD. Various techniques can be used to stretch and compress laser pulses. In this project, a prism pulse compressor used for compressing stretched pulses was built. A 200nm supercontinnum generated in an all normal dispersion photonic crystal fibre (ANDi-PCF) was compressed using the prism pulse compressor from 2ps to 140fs. The experiment and physical interpretation presented in this project suggest that a shorter pulse duration less than the measured 140fs of the compressed supercontinnum can be obtained.
AFRIKAANSE OPSOMMING: 'n Ultra-vinnige laser puls kan beskryf word in tyd of frekwensie. As die tyd-bandwydte produk van ‘n ultra-vinnige puls nie bevredig is nie, dan is die puls uitgerek. Hierdie uitrekking kan beskryf word in tyd of frekwensie. In tyd word dit tjirp genoem en in frekwensie groep vertraging dispersie. Verskeie tegnieke kan gebruik word om ‘n laser puls te rek of saam te pers. In hierdie projek is ‘n prisma puls kompressor gebou om uitgerekte pulse saam te pers. ‘n 200nm bre e bandwydte puls (“supercontinuum”) is gegenereer in ‘n fotoniese kristal optiese vesel wat uitsluitlik normale dispersie toon (ANDI-PCF) en die puls is toe saamgepers met behulp van die prisma puls kompressor van‘n oorspronklike 2ps na 140fs. Die eksperiment en fisiese interpretasie wat in hierdie projek aangebied word dui daarop dat ‘n nog korter puls, minder as die gemete 140 fs, verkry kan word deur die bre e bandwydte puls verder saam te pers.
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Emile, Olivier. "Manipulation d'atomes d'hélium métastable par laser: effet Sisyphe magnétique." Phd thesis, Université Pierre et Marie Curie - Paris VI, 1993. http://tel.archives-ouvertes.fr/tel-00011888.
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Ce mémoire présente l'étude du refroidissement d'atomes par laser en présence d'un champ magnétique transverse faible (effet Sisyphe magnétique) sur une transition J = 1 → J' = 1. La première partie de ce travail est consacrée à l'optimisation d'un jet supersonique d'hélium métastable sur lequel nous avons effectué nos expériences de refroidissement laser. L'optimisation du jet en vue de piéger les atomes dans un piège magnéto-optique est aussi décrite. La deuxième partie consiste en une description de l'effet Sisyphe magnétique sur l'hélium métastable. Après une présentation qualitative du mécanisme mettant en jeu l'effet Sisyphe magnétique, nous discutons les résultats expérimentaux à la lumière de calculs théoriques détaillés.
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Kaiser, Robin. "Manipulation par laser d'hélium métastable: effet Hanle mécanique, refroidissement sous le recul d'un photon." Phd thesis, Université Pierre et Marie Curie - Paris VI, 1990. http://tel.archives-ouvertes.fr/tel-00011870.
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Ce mémoire présente un nouveau mécanisme de refroidissement d'atomes par laser: les résonances noires sélectives en vitesse. La première partie de ce travail est consacrée à la description d'un jet supersonique d'hélium métastable, refroidi par cryogénie, sur lequel nous avons effectué nos expériences de refroidissement par laser. Un deuxième chapitre, dans lequel nous introduisons les outils théoriques nécessaires pour l'analyse du chapitre III, nous donne l'occasion de présenter l'effet Hanle mécanique. Il s'agit là d'une résonance très fine de la force de pression de radiation sur un atome ayant un sous-niveau Zeeman piège, lorsqu'on varie le champ magnétique autour de zéro. Le troisième chapitre consiste finalement en une présentation des résonances noires sélectives en vitesse. A côté d'une étude théorique détaillée, nous présentons la mise en évidence expérimentale de cet effet: nous avons en effet réussi à comprimer à une dimension la distribution des vitesses en-dessous de la vitesse de recul \hbar k/M d'un seul photon.
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Savard, Guy. "Laser spectroscopy of neutron deficient gold and platinum isotopes." Thesis, McGill University, 1988. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=75851.
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A new method for on-line laser spectroscopy of radioactive atoms based on the resonant ionization spectroscopy of laser desorbed radioactive samples has been devised. An experimental set-up has been installed on-line at the ISOCELE mass separator in Orsay (France) and experiments have been performed on the transitional nuclei region around Z = 79. Four new isotopes $ sp{194,196,198,199}$Au have been added to the series of the isotopic shift measurements in gold and results on the neutron deficient isotopes down to $ sp{186}$Au have been obtained, confirming the nuclear ground-state shape transition from oblate to prolate between $ sp{187}$Au and $ sp{186}$Au. The first isotopic shift measurements on radioactive platinum have been obtained on $ sp{186,188,189}$Pt. Indications of a shape transition have been observed between $ sp{186}$Pt and $ sp{188}$Pt. The extracted experimental changes in mean square charge radii $ delta$ $ sp{A,A{ sp prime}}$ along isotopic chains are compared to self-consistent Hartree-Fock plus BCS calculations.
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Kellerbauer, Alban. "Production of a cooled ion beam by manipulation of 60-keV ions into a radio-frequency quadrupole ion guide." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape9/PQDD_0025/MQ50804.pdf.
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Ng, Li Na. "Manipulation of particles on optical waveguides." Thesis, University of Southampton, 2000. https://eprints.soton.ac.uk/15499/.
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A theoretical and experimental study on the optical trapping and propulsion of latex, gold aggregate and colloidal gold particles with average radius of 1.5µm, 250nm and 10nm respectively, in the evanescent region of an illuminated ion-exchange channel waveguide is documented in this thesis. Optimisation of light-induced forces exerted on a particle on a waveguide relies on two important factors, firstly a maximisation of the intensity and intensity gradient present in the guide-cover interface and secondly, an optimisation of the polarizability of a particle. To this end, a transcendental equation was established and was used to generate design curves for the normalised waveguide thickness required for achieving a maximum gradient force on the guide-cover interface of a waveguide for a specific set of indices. A study based on Mie theory for the investigation of morphology dependent resonance exhibited by a spherical particle is described. The dependence of resonances on particle radius, index of the sphere with respect to the surrounding medium, absorption, plasmon resonance and symmetry of the incident beam has been investigated. In particular, a simplification of the Mie model was carried out to derive Rayleigh expressions of cross sections from which particle polarizability originates. The validity of the Rayleigh model was assessed with respect to the limiting particle radius. Based on a semi-classical approach, a derivation of light-induced forces applying to a Rayleigh sphere in the cover region of a waveguide is detailed. The three main optical force components produced are (i) a forward scattering and absorption force due to the intensity of the incident radiation which accounts for propulsion of particles, (ii) a transverse gradient force due to an intensity gradient generated by a decaying evanescent field and finally (iii) a lateral gradient force which arises from the near-Gaussian intensity distribution on a channel waveguide. A comparison of the relative magnitude of each component is described, with additional forces due to gravity, buoyancy and Brownian motion studied. Factors affecting the propulsion of a gold nanoparticle were investigated. It was shown that the particle velocity is linearly dependent upon the waveguide modal power, increases with a wavelength closer to plasmon resonance in the case of a Rayleigh gold particle, is stronger for TM polarized light, increases with a larger change in the waveguide refractive index and is maximum for a minimum modesize. For the first time, under the action of light-induced forces generated on the surface of an optical waveguide, colloidal gold particles are propelled in the direction of wave propagation reaching at a maximum velocity of 10µm/s for a modal power of 500mW at l=1.047µm. Results obtained will be useful for future applications in particle sorting, fluorescence sensing and surface enhanced Raman sensing of chemical species.
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Cheng, Hongmei. "Feasibiliy studies for laser spectroscopy of thorium ions in a Paul trap." Thesis, McGill University, 1997. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=27299.
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This thesis evaluates the suitability of Thorium(Th) ions for optical spectroscopic measurements in a Paul trap. A $ sp{232}Th$ sample, placed near the ring electrode, is evaporated with a Nd:YAG laser pulse and then selectively ionized by a synchronized dye laser pulse. Ions created inside the trap follow stable orbits and are cooled by hydrogen buffer gas.The stability and trapping efficiency for the ions are examined at various trap operating conditions. The motion of the ions in the trap is studied with particular attention to volume occupied by the ions in the phase space. With the trap operating at optimum conditions for stability and spectral resolution, laser-induced fluorescence measurements at selected rf phase angles are applied to five optical transitions of Th ions. Results indicate that two transitions are most suitable for spectroscopic studies and 60-80 ions are required to produce a spectrum with signal-to-background ratio of 1:1.
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Shelbaya, Olivier. "Laser spectroscopy of rare Rubidium isotopes and development of data analysis software at TRIUMF." Thesis, McGill University, 2012. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=110585.
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TRIUMF, Canada's national laboratory for nuclear and particle physics has been peering into the shape and structure of highly unstable, rare isotopes. Employing the method of collinear fast-beam laser spectroscopy, the nuclear ground state spin, hyperfine moments and charge radii can be determined. The laser spectroscopy group at TRIUMF has used this method to investigate the properties of rubidium isotopes, where 76-98 Rb had been previously studied at ISOLDE by Thibault et al. Laser spectroscopy was performed at TRIUMF on both the neutron deficient 74-76 Rb, providing insight into the behaviour leading up to the proton drip line. On the neutron rich end, a programme is in place to extend measurements into the highly deformed 98-100 Rb. Preliminary measurements of the spectra of the spin-0 isotope 92 Rb have been carried out, on beams with intensities of 10^7 per second, representing the first time heavy rubidiums have been produced and studied spectroscopically at TRIUMF. These measurements have been carried out in conjunction with the implementation of a new MCS based data acquisition system, greatly improving the data collection and analysis capabilities of the laser spectroscopy group.TRIUMF, le laboratoire national canadien pour la recherche en physique nucléaire et en physique des particules, a entrepris l'étude de la forme ainsi que la structure d'isotopes rares et hautement instables. En employant la méthode de la spectroscopie colinéaire utilisant des faisceaux atomiques à haute vitesse, le spin nucléaire ainsi que les moments nucléaires et le rayon de charge peuvent êtres determinés. Le groupe de spectroscopie au laser de TRIUMF a usé de cette méthode pour observer les propriétés fondamentales des isotopes du rubidium, famille isotopique pour laquelle les isotopes 76 Rb à 98 Rb ont déjà été étudiés au laboratoire ISOLDE par Thibault et al. En premier lieu, les isotopes déficitaires en neutrons 74 Rb - 76 Rb ont étés observés, permettant l'étude du rayon de charge nucléaire dans le régime menant à la ligne de limite de stabilité. Du côté riche en neutrons, un programme est en cours pour entreprendre l'étude des isotopes 98 Rb - 100 Rb, ces derniers étant hautement déformés. Des mesures péliminaires sur le spectre hyperfin de l'isotope 92 Rb, au spin nucleaire de 0, ont été réalisées, avec un rendement ionique de l'ordre de 10^7 par seconde. Ceci représente la première fois que des rubidiums lourds ont été produits et étudiés spectroscopiquement à TRIUMF. Ces nouvelles mesures ont été prises grâce à un nouveau système basé sur le principe d'un MCS, permettant l'augmentation de la capacité ainsi que de la qualité de l'acquisition de données.
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Rizzo, Benjamin. "Laser monitoring system for the ALICE ITS." Click here for online access in Bluebrary, 2008. http://hdl.handle.net/10504/109.
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Hendricks, Jason Mark. "Holographic laser resonators." Thesis, University of Southampton, 2002. https://eprints.soton.ac.uk/15485/.
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The work presented within this thesis details the development and characterisation of a CW solid-state adaptive resonator that uses phase-conjugation to actively correct for phase distortions present within the resonator loop. It is shown that the phase-conjugate of a given beam can be produced by the process of degenerate four-wave mixing inside a gain medium. In this scheme two mutually coherent beams overlap within a population inverted region of a laser amplifier and the subsequent interference pattern between them spatially hole burns a grating into the gain. The diffraction efficiency of such gain-gratings is studied both theoretically and experimentally and it is shown that, due to the stored inversion, CW phase-conjugate reflectivities of greater than 100 can be achieved in Nd:YVO4. Using this gain four-wave mixing scheme an adaptive resonator is built that is capable of oscillating with a phase-conjugate mode. The ability of the volume gain-grating to encode and react dynamically to phase distortions present within the resonator loop ensures that the phaseconjugate output beam from the resonator always remains a faithful reproduction of the beam used to seed the resonator. The interactions occurring within the resonator are modelled and a resonator capable of producing an 11.6 W near-diffraction limited output is demonstrated. The powerscaling capabilities of such lasers is then considered and it is shown that the output power can be increased whilst maintaining phase-conjugate oscillation. It is shown that a phase-conjugate output of 6 W can be scaled to 11.7 W with the addition of a power amplifier placed into the existing setup.
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Schacht, Michael. "Spin state detection and manipulation and parity violation in a single trapped ion /." Thesis, Connect to this title online; UW restricted, 2000. http://hdl.handle.net/1773/9664.
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Kazer, Andrew. "Development of a 1.54µm Yb:Er:glass laser pumped by a Nd:YAG laser." Thesis, University of Southampton, 1990. https://eprints.soton.ac.uk/404738/.
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The development of a laser source, operating at the wavelength of 1.54µm, using the scheme of ytterbium:erbium:glass, longitudinally pumped by a Nd:YAG laser at 1.064µm, has been investigated. The first pulsed Nd:YAG laser pumped Yb:Er:glass laser system was successfully demonstrated. This system was operated free-running, Q-switched, mode-locked, and combined Q-switched and mode-locked, all with good output characteristics. A free-running output power of 2.25W in a 3.5ms pulse was achieved, with 13% slope efficiency, and a threshold incident pump power of 37W. Q-switched pulses of 10kW peak power and 60ns width were obtained, using a LiNbO3 electro-optic device. Active mode-locking, using an acousto-optic device, gave pulses of 50W peak power and 70ps duration. Combined Q-switched and mode-locked operation, gave a peak power of 2kW with pulses 85ps wide. The first cw laser operation o bulk Yb:Er:glass, pumped by a cw Nd:YAG laser, was also demonstrated. Using high reflectivity mirrors an absorbed power threshold as low as 500mW was achieved. An output of 21mW was obtained for 1.05W absorbed pump power. Q-switched, and mode-locked operation, for this cw laser, have also been demonstrated, with good characteristics. A detailed discussion is given of the design considerations leading to successful laser performance. A rate equation analysis, including energy transfer from Yb to Er, and volumetric considerations, is presented. A detailed study is made of the theoretical aspects of thermal effects, such as lensing and birefringence, and their practical implications, which are an important feature of the laser design.
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Zhao, Wenzheng. "Laser spectroscopic studies of hafnium ions confined in a Paul trap." Thesis, McGill University, 1995. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=40301.
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A Paul trap has been constructed for laser spectroscopic studies of the isotope shifts (IS) and hyperfine structures (hfs) of radioactive isotopes. With a sample placed near the inner surface of the ring electrode, the target atoms are evaporated by a Nd:YAG laser pulse, and then selectively ionized inside the trap by a synchronized dye laser pulse through resonance ionization spectroscopy (RIS). A cw beam from a ring dye laser is used to probe the ions, and laser-induced fluorescence (LIF) is monitored for spectroscopic measurements. The stored ions can also be analyzed by the ion-ejection time-of-flight spectrum. With an ultra-high vacuum base pressure, Hf ion storage times of one hour can be readily achieved by introducing H$ sb2$ as a buffer gas. It is demonstrated that with a very dilute sample, Hf ions can be accumulated in the trap through successive heating and RIS pulses. Through LIF measurements, both the ion cooling time and the dependence of the mean ion kinetic energy on the RF phase and trap operating conditions have been studied. A phase-locked counting technique has been applied to improve the spectroscopic resolution. The hfs of $ sp{177}$Hf and $ sp{179}$Hf with the transition a $ rm sp2D sb{3/2}$--$z sp4{ rm F} sbsp{5/2}{ circ} ( lambda$ = 340 nm) in HfII has been studied with a resolution of about 1 GHz, and their hfs A and B constants have been deduced. The IS of the radioactive $ sp{172}$Hf has been carried out with a sample containing $7 times10 sp{11} sp{172}$Hf atoms. Based on the observation of the laser-induced formation of HfH, a new spectroscopic method capable of selectively suppressing the ion population of a particular contaminant isotope has been developed to enhance the $ sp{172}$Hf signal-to-noise ratio. Deduced changes of mean-square nuclear charge radii in Hf, together with the existing data in the literature, are discussed and compared with theoretical variations obtained from Finite-Range Droplet Model calculations.
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Rivers, Paul Edmund. "Pulsed laser deposition of chalcogenide glass materials for potential waveguide laser applications." Thesis, University of Southampton, 2000. https://eprints.soton.ac.uk/15493/.
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There are many applications for small scale, solid state lasers in the near infrared, where conversely there are very few such devices. A lasing device in a rare earth doped gallium-lanthanum-sulphide thin film is attractive due to emission at wavelengths in the 2 to 5 µm region where many gasses and liquids have fundamental vibrations and overtones and so are detectable. This region also covers the 3 to 5 µm atmospheric 'windows'. Some examples of such detection is presented in this thesis. Using Pulsed Laser Deposition, a relatively new deposition technique, we are able to grow thin films of the chalcogenide glass; gallium-lanthanum-sulphide, gallium-sodium-sulphide and variations of oxysulphides, on a variety of substrates. EXAFS measurements have shown that some of the elements in the glass structure change their bonding arrangement when grown at different energy density producing 'wrong bonds'. This points to the origin of the increased absorption and shift of the optical bandgap which is seen in the materials. It is this tail absorption which ultimately prevented the production of an actual solid state, rare earth laser device. These amorphous semiconductors have a transmission range from the visible through to the mid infrared part of the spectrum. Chalcogenides can be photomodified. i.e. they have an ability to change refractive index when illuminated with photons whose energies lie in the optical bandgap of the material. This process can be reversible or irreversible depending on post deposition treatment and so gives them potential applications such as optical memory, holographic recording media, lithographically written waveguide structures and potentially laser mediums. For such uses a detailed knowledge of the chalcogenide materials optical parameters is needed. A novel technique for the optical characterisation of the thin films has been developed which has is able to measure differences in refractive index to an accuracy of 8.5 x 105. We are able to map refractive index changes across an entire surface and more uniquely whilst they are occurring during, and after, photomodification or heating.
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Dunning, Alexander. "Coherent atomic manipulation and cooling using composite optical pulse sequences." Thesis, University of Southampton, 2014. https://eprints.soton.ac.uk/364735/.
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The laser cooling of atoms to ultracold temperatures has propelled many groundbreaking advances in fundamental research and precision measurement, through such applications as quantum simulators and interferometric sensors. Laser cooling remains, however, highly species-selective, and techniques for its application to molecules are still in their infancy. This thesis broadly concerns the development of laser cooling schemes, based on sequences of coherent optical pulses, which can in principle be applied to a wide range of species. We describe a cooling scheme, in which a velocity-selective impulse analogous to that in Doppler cooling is generated by a light-pulse Ramsey interferometer, and present a proof-of-concept demonstration of the scheme using ultracold rubidium-85 atoms as a test-bed. We realise an interferometer for the atoms, as they are in free-fall after release from a magneto-optical trap, by inducing stimulated Raman transitions between their ground hyperfine states. We provide a comprehensive characterisation of these Raman light-pulse interferometer optics, where particular attention is paid to light shift effects. Raman pulses, and indeed coherent operations in any quantum control system, unavoidably suffer from systematic errors in the control field intensity and frequency, and these lead to reductions in pulse fidelity and readout contrast. In parallel to the work on interferometric cooling in this thesis, we report our preliminary investigations into composite pulses, whereby `naive' single pulses are replaced by sequences of rotations with tailored durations and phases, for improving pulse fidelity in the presence of inhomogeneities. We find that composite pulses can indeed be highly effective in our cold atom system, and propose that their application in such devices as interferometric sensors is a promising prospect.
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Darby, Mark Stuart Bennett. "Femtosecond pulsed laser deposition." Thesis, University of Southampton, 2009. https://eprints.soton.ac.uk/65796/.
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This thesis investigates two variations of the conventional pulsed laser deposition (PLD) technique. The first technique is femtosecond PLD, whereby the laser used to ablate the target has a significantly higher peak intensity and shorter pulse duration as compared to conventional nanosecond lasers more commonly used for PLD. Experiments have been conducted on the growth of Nd:Gd is presented. Experimental results will show the composition and lattice parameter of a film can be controlled by changing the relative laser fluences on the two targets. Films have been grown with enough extra Ga to compensate for the deficiency that commonly occurs when depositing from only one Nd:GGG target.
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Eckold, Matthew. "The rotating cavity laser." Thesis, University of Southampton, 2015. https://eprints.soton.ac.uk/374674/.
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This thesis describes a new technique for mitigating the detrimental thermal phenomena that often limit the power scaling potential of solid state lasers. The unavoidable heating effect that arisesfrom the quantum defect leads to a degradation in beam quality, reduced efficiency and, eventually catastrophic failure. However, lasing processes occur on a faster time scale than those associated with heat flow through a typical laser gain medium. This is made use of whenever a laser is operated in a QCW mode, the laser is operated within an adiabatic window then turned off whilst the gain medium cools. This adds a constraint to the maximum duty cycle of the laser and thus reduces the average power output. Alternatively to separating the two processes in time they can be separated in space. The thermal process can be separated from lasing with the introduction of motion to the system. By passing a collinear pump beam and laser mode through a rotating periscope placed in front of a gain medium the lasing spot can be moved into cold material before heat is able to flow. We call this arrangement the Rotating Cavity Laser (RCL). Unlike previously demonstrated solid state lasers which make use of motion, the RCL keeps the gain medium stationary. This allows it to be heat sunk directly, simplifying the mechanical arrangement. Within this thesis the first results from an RCL are presented with theoretical predictions of the influence motion has both on the lasing and thermal properties of the system. Attention is paid to the regime where stimulated emission is negligible and the losses due to motion are therefore greatest. The analysis of this regime allowed the threshold under motion to be calculated and the approach was verified experimentally. The RCL architecture allowed 120 W of 1064 nm light to be generated from a single end pumped Nd:YAG ceramic slab. The presence of moving intracavity components was found to have consequences for the stability of the power output. When producing 72 W the output power varied with a standard deviation of 2.8%, importantly this variation was cyclic suggesting it would be straightforward to correct by modulating the pump source. Whilst excellent beam quality was found at low powers the M2 became poor as the pump power increased. At output powers less than 51 W the beam quality was found to be constant over a rotation period. It is postulated that the increase in M2 at high pump powers, as well as the increase in variation in beam quality over a rotation period, is partly due to the presence of a thermally induced wedge compromising the alignment of the resonator. A number of experiments are also presented that demonstrate the effectiveness of introducing motion as a method to reduce the thermal load within a laser gain medium. Losses due to stress induced birefringence were reduced from 8% for the stationary case to less than 0.5% by rotating the periscope. The aberrating nature of the thermal lens present in the RCL was also investigated by passing a 1064 nm probe beam through it. When the periscope was stationary the probe beam degraded from an M2 of 1.1 to 2.0 under 16.3 W of pump power. Introducing motion and pumping the slab with 180 W resulted in the M2 increasing to 1.4, clearly demonstrated the greater resilience a system with motion has to detrimental thermal effects.
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May-Smith, Timothy Christopher. "Pulsed laser deposition of thick multilayer garnet crystal films for waveguide laser devices." Thesis, University of Southampton, 2005. https://eprints.soton.ac.uk/65499/.
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The main aim of this project was to use the technique of pulsed laser deposition (PLD) to fabricate thick multilayered garnet crystal planar waveguides with rare-earth ion doped cores for use as planar waveguide laser devices. Planar waveguides are of interest because of the implications of their structure, which allows for lasing, pumping and heat dissipation to each have a unique axis of operation, and the confinement properties of planar waveguide lasers result in lower pump power thresholds, higher gains per unit pump power and higher efficiencies than their bulk counterparts. Thick planar waveguide lasers are desirable because they can be pumped by high power diode laser arrays, and suffer less from the detrimental effect of particulates (a practically unavoidable side effect of the PLD technique). The use of multilayers allows a device with a high numerical aperture to be fabricated and the careful choice of the cladding layer thicknesses and refractive indices allows good beam quality output to be produced using diode pumping. Other aims of the project were to fabricate a self-imaging waveguide amplifier and explore other applications of thick garnet crystal films such as the possibility of using a highly doped thick film as a thin-disk laser device. Now that the technique of thick garnet crystal film deposition via multiple growth runs has been established, the potential of thick garnet crystal films needs to be exploited. Multilayer structures with more ideal geometries need to be fabricated to make optimal waveguide laser devices and difficulties resulting from thermal expansion mismatch need to be addressed so that side-pumping can be performed with diode laser arrays.
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Magrakvelidze, Maia. "Nuclear dynamics and ionization of diatomic molecules in intense laser fields." Thesis, Manhattan, Kan. : Kansas State University, 2009. http://hdl.handle.net/2097/2283.
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Taverner, Domino. "Generation and manipulation of short optical pulses in fibre based systems." Thesis, University of Southampton, 1996. https://eprints.soton.ac.uk/398738/.
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This thesis presents experimental and computational work on a variety of fibre based systems covering the generation, transmission, manipulation and amplification of short optical pulses (hundreds of femtoseconds to tens of picoseconds). The construction and characterisation of an all-polarisation-maintaining fibre figure-8, passively mode-locked laser is presented. This was the first all-fibre passively mode-locked cavity constructed entirely of high birefringence, polarisation maintaining components. This enabled the generation of a single polarisation Eigen-state within the cavity, resulting in a source of high quality 2.3ps-6ps solitonic pulses with excellent environmental stability, despite the considerable length of the device (395m). A computational model of a dispersion compensated standard fibre link using a fibre based four-wave mixing, midpoint spectral inversion (MPSI) technique was developed to provide qualitative and quantitative support to a 50km experimental system for the transmission of 6ps solitonic pulses. This model was then used to provide an estimate of the limitations to such systems presented by higher order dispersion, the results suggesting that links greater than 2500km at single channel bit-rates of 50GBit/s could be feasible. The development of photorefractive fibre Bragg gratings has produced one of the most important and flexible fibre devices. Experimental and computational investigations of the interaction of short pulses with both uniform and linearly chirped gratings are presented, giving a useful insight into their dispersive effects and limitations for their use in more complex systems. The importance of apodisation for reducing the energy scattering from pulses after multiple reflections was clearly demonstrated through numerical modelling of such systems. The application of long, linearly chirped fibre Bragg gratings to the compensation of chromatic dispersion in step-index fibres at potential bit-rates approaching 50GBit/s was demonstrated experimentally with the transmission of 16ps pulses over 100km. The use of two cascaded 4cm gratings exploited the linearity of these devices to further push the limits of compensation available. One of the few limitations of fibre based short pulse sources is the relatively low pulse energies produced. This problem had been tackled through the use of chirped pulse amplification (CPA) to circumvent the limitations imposed by fibre nonlinearities to amplification in EDFAs, however the problems of energy extraction from the amplifier fibre remained. The development and application to CPA of a large mode-area EDFA designed to improve pulse energy extraction is presented. The generation of 32?J pulses directly from the amplifier represented a significant increase in both energy and pulse quality over previously reported systems, demonstrating the potential of such amplifier designs for a range of high energy/intensity pulse applications.
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Cooper, Merlin Frederick Wilmot. "Measurement and manipulation of quantum states of travelling light fields." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:79164748-ebb3-48e2-b4d4-1a4766d29217.
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This thesis is concerned with the generation of non-classical quantum states of light, the photon-level manipulation of quantum states and the accurate tomography of both quantum states and quantum processes. In optics, quantum information can be encoded and processed in both discrete and continuous variables. Hybrid approaches combining for example homodyne detection with conditional state preparation and manipulation are gaining increasing prominence. The development and characterization of a time-domain balanced homodyne detector (BHD) is presented. The detector has a bandwidth of 80 MHz, a signal-to-noise ratio of 14.5 dB and an efficiency of 86% making it well-suited to pulse-to-pulse measurement of quantum optical states. The BHD is employed to perform quantum state tomography (QST) of non-classical multi-photon Fock states generated by spontaneous parametric down-conversion. A detailed investigation of the mode-matching between the local oscillator used for homodyne detection and the generated Fock states is presented. The one-, two- and three-photon Fock states are reconstructed with a combined preparation and detection efficiency exceeding 50%. Fock states have a number of applications in quantum state engineering, where non-classical ancilla states and conditional measurements enable photon-level manipulation of quantum states. Fock state filtration (FSF) is investigated - an example of a post-selected beam splitter which is a basic building block for many quantum state engineering protocols. A model is developed incorporating the effect of experimental imperfections. An experimental implementation of a Fock state filter is fully characterized by means of coherent-state quantum process tomography (QPT). The reconstructed process is found to be consistent with the model. The filter preferentially removes the single-photon component from an arbitrary input quantum state. Calibration of optical detectors in the quantum regime is discussed. Quantum detector tomography (QDT) is reviewed and contrasted with a new technique for performing QST with a calibrated detector known as the fitting of data patterns (FDP). The first experimental characterization of a BHD is performed by probing the detector with phase-averaged coherent states. The FDP method is shown to be applicable to the estimation of quantum processes, where a detector response is not assumed - thus demonstrating the versatility of the FDP approach as a new method in the quantum tomography toolbox.
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Muldoon, Cecilia. "Control and manipulation of cold atoms in optical tweezers." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:920933c8-441c-4d59-a4f4-87f8c799a820.
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The ability to address and manipulate individual information carriers in a deterministic, coherent, and scalable manner is a central theme in quantum information processing. Neutral atoms trapped by laser light are amongst the most promising candidates for storing and processing information in a quantum computer or simulator, so a scalable and flexible scheme for their control and manipulation is paramount. This thesis demonstrates a fast and versatile method to address and dynamically control the position (the motional degrees of freedom) of neutral atoms trapped in optical tweezers. The tweezers are generated by using the direct image of a Spatial Light Modulator (SLM) which can control and shape a large number of optical dipole-force traps. Trapped atoms adapt to any change in the potential landscape, such that one can re-arrange and randomly access individual sites within atom-trap arrays. A diffraction limited imaging system is used to map the intensity distribution of the SLM onto a cloud of cold atoms captured and cooled using a Magneto Optical Surface Trap (MOST).
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Møller, Morten. "Optimizing the structure of scanning probes for atomic manipulation." Thesis, University of Nottingham, 2017. http://eprints.nottingham.ac.uk/44916/.
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Scanning probe microscopy (SPM) allows us to directly measure the interactions between a probe and a sample at the atomic scale. Techniques such as non-contact atomic force microscopy (NC-AFM), allows us to to characterize the forces present on a surface, resolve the atomic structure of molecules or examine their chemical properties, while scanning tunneling microscopy (STM) allows their electronic properties to be characterized. As the interactions take place at the atomic scale, the atomistic state of the probe apex plays a crucial role. In AFM, it is the atomic scale forces between the outermost atoms of the probe and surface that are dominant, while for STM the density of states (DOS) that contribute to tunneling are crucial. Therefore, understanding and controlling the tip termination is crucial to derive meaningful interpretations from experimental data. In this thesis, the role of the tip termination is examined for various surfaces and situations. We find that determining the "right" tip state depends critically on the experiment and several general strategies for shaping the tip apex into a preferred state are therefore outlined. H:Si(100) surfaces were used as a substrate for lithographic patterning using STM. We have successfully implemented an automated extraction routine for performing large scale patterning with high fidelity and single atom specificity. Our ultimate goal is to combine the extraction routine with SPM image recognition software to allow analysis and manipulation of atomic scale features without human intervention. To perform manipulations reliably, the tip influence on "what we see" (tip imaging states), or specifically on what the recognition software can identify, needs to be considered. We find, counter-intuitively, that atomic scale manipulation with the highest fidelity occurs when silicon dimers are observed as rows as opposed to when atomic resolution imaging occurs. The tip state influence on measuring surface diffusion of PTCDA on Ag(110) surfaces, was also investigated. We find that the adsorption kinetics of diffusing molecules can only be detected for specific tip imaging states. To allow examination with no-human intervention, the tip state needs to be carefully considered, and a combination of analytical and spectroscopic tools needs to be implemented in conjunction with the experiment. Additionally, characterization of the tip apex was investigated at the tunnel junction between a STM tip and a metal surface using field emission measurements. Our results suggest that field emission measurements performed at the tunnel junction are sensitive to changes in the nanoscopic/mesoscopic tip apex structure, thus opening up the possibility of automating the process of characterization the tip apex.
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Hosni, F. "Faisceaux exotiques par méthode ISOL Développements pour l'ionisation par laser et l'ionisation de surface." Phd thesis, Université Paris Sud - Paris XI, 2004. http://tel.archives-ouvertes.fr/in2p3-00024594.
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Ces travaux s'inscrivent dans le cadre du programme R et D PARRNe (Production d'atomes radioactifs riches en neutrons ). Ce programme vise d'une façon générale à déterminer les conditions optimales pour produire d'intenses faisceaux d'isotopes riches en neutrons. Cette thèse traite des multiples aspects techniques liés à la production d'isotopes radioactifs séparés en ligne (ISOL). Elle porte principalement sur le développement de l'ensemble cible-source qui est l'élément clé pour les projets comme SPIRAL-2 ou EURISOL. La première partie présente les différentes méthodes utilisant la fission comme réaction exploitée en ligne ainsi que leur comparaison : fission thermique, fission induite par des neutrons rapides et photofission. L'expérience faite au CERN a permis de valider la photofission comme mode prometteur pour la production d'ions radioactifs, c'est pour cela que l'IPN d'Orsay a décidé de construire un accélérateur linéaire d'électrons auprès du Tandem d'Orsay (ALTO). La deuxième partie de cette thèse a porté sur le développement de cibles d'uranium. Des techniques d'analyse comme la diffraction X et la microscopie électronique à balayage ont été utilisées. Elles ont permis de déterminer les caractéristiques chimiques et structurales de cibles de carbure d'uranium portées à différentes températures de chauffage. Après la production le processus d'ionisation est étudié. Deux types de sources ont été mises en oeuvre : la première est une source à ionisation de surface et la deuxième est une source basée sur l'ionisation résonante par laser. Ces deux types de sources seront utilisées pour le projet ALTO.
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Robertson, Elaine Elder. "Manipulation of the photorefractive properties of ferroelectric waveguides by ion-beam implantation." Thesis, University of Southampton, 1997. https://eprints.soton.ac.uk/394571/.
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This thesis presents the results of a study of ion-beam implantation (IBI) and the effect it has on the photorefractive properties of ferroelectric waveguides. IBI was used to create waveguides in strontium barium niobate (SBN) and lithium niobate in addition to modifying the properties of annealed proton exchanged (APE) channel waveguides fabricated in lithium niobate. Low loss SBN planar waveguides were fabricated by ion-beam implantation. These waveguides represent the first reported in this material to have preserved their photorefractive properties. Two-beam coupling was used as a technique to measure the photorefractive gain and response time in the waveguides; it was observed that unlike IBI waveguides in BaTiO3 and KNbO3, the gain direction had not reversed and the response time had decreased by two orders of magnitude. Evidence of a nonlinear dependence of the response time on intensity indicates that these results are due to oxygen vacancies, induced by the implant, which act as shallow traps. This hypothesis was strengthened when IBI was used as a post-processing technique on APE LiNbO3 channel waveguides. It was observed that for a high enough implant dose of H+ ions, the photorefractive effect was dramatically reduced. This is attributed to the formation of oxygen vacancies due to the implant which reduce the photovoltaic currents within the material; this procedure is thought to be similar to the mechanism responsible for reducing the photorefractive effect in MgO doped LiNbO3. These effects were not observed in planar Fe:LiNbO3 waveguides formed by ion-beam implantation. KTP channel waveguides were fabricated using ion-exchange. The photorefractive susceptibility of these waveguides was assessed and compared to APE LiTaO3 channel waveguides. It was observed that the photorefractive susceptibility of KTP was appreciably lower than that of LiTaO3.
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Sauer, Jacob A. "Cold Atom Manipulation for Quantum Computing and Control." Diss., Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/4809.
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Devices that exploit the properties of quantum mechanics for their operation can offer unique advantages over their classical counterparts. Interference of matter waves can be used to
dramatically increase the rotational sensitivity of gyroscopes. Complete control of the quantum evolution of a system could produce a new powerful computational device known as a quantum computer. Research into these technologies offers a deeper
understanding of quantum mechanics as well as exciting new insights into many other areas of science. Currently, a limiting factor in many quantum devices using neutral atoms is accurate motional control over the atoms. This thesis describes two recent advancements in neutral atom motional control using both magnetic and electromagnetic confining fields. Part I reports on the demonstration of the first storage ring for neutral atoms. This storage ring may one day provide the basis for the world's most
sensitive gyroscope. Part II describes the optical delivery of neutral atoms into the mode of a high-finesse cavity for applications in quantum computing and communication.
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Yang, Weijia. "Femtosecond laser writing in transparent materials." Thesis, University of Southampton, 2008. https://eprints.soton.ac.uk/65510/.
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Optical waveguides (type-I), with perfect mode matching to the standard single-mode fibre and with an overall insertion loss of ~1 dB, have been demonstrated in high index bismuth borate glass by femtosecond laser direct writing. Broadening of the transmitted light source by as much as 500 nm was demonstrated through a waveguide with a length of 1.8 cm. Finally, passive waveguide components such as Y-splitters and directional couplers have also been fabricated using this writing technique. Self-assembled, sub-wavelength periodic structures (type-II) are induced in fused silica by a tightly focused, linearly polarized, femtosecond laser beam. Two different types of periodic structures, the main one with period (ΛE) in the direction of the laser beam polarization and the second with period (Λk) in the direction of the light propagation, are identified from the cross-sectional images of the modified regions using scanning electron microscopy. The period ΛE is proportional to the wavelength of the writing laser and the period Λk in the head of the modified region remains approximately the wavelength of light in fused silica. A new phenomenon in ultrafast laser processing of transparent optical materials, in particular silica glass, manifested as a change in material modification by reversing the writing direction, is observed. The effect resembles writing with a quill pen and is interpreted in terms of new physical effect - anisotropic trapping of electron plasma by a tilted front of the ultrashort laser pulse. Different types of modifications are induced in fused silica by controlling the pulse front tilt. Birefringent modification is demonstrated in the chalcogenide glass by femtosecond laser direct writing. The optical axis of the birefringent region is not determined by the laser polarization direction. It is observed that the information on the direction of writing can be recorded and be rewritable in the chalcogenide glass. Finally, a unique non-reciprocal photosensitivity is identified for the lithium niobate crystal for ultrafast laser direct writing. Therefore, in a non-centrosymmetric medium, modification of the material can be different when light propagates in opposite directions.
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Maker, Gareth Thomas. "Diode laser pumped solid state lasers." Thesis, University of Southampton, 1990. https://eprints.soton.ac.uk/397281/.
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This thesis deals with the development of diode laser pumped solid state lasers. The earliest work presented enabled 125W peak power, single frequency Q-switched pulses to be obtained from a 100mW diode laser pumped Nd:YAG laser. Using a 500mW diode laser as a pump source for C.W. Nd:YAG and Nd:YLF oscillators an Yb:Er fibre laser was pumped, producing 0.75mW C.W. power at a wavelength of 1.56µm. Acousto-optic mode-locking techniques were used to provide C.W. mode-locked pulse durations in Nd:YAG and Nd:YLF of 55ps and 18ps respectively, at repetition rates of 240MHz. Frequency modulation mode-locking was shown to be a superior technique, giving pulse durations of 11.5ps and 10ps in diode laser pumped Nd:YAG and Nd:YLF oscillators respectively. FM operation of diode laser pumped Nd:YAG lasers was investigated, yielding a maximum FM bandwidth of 70GHz. Spatial hole burning was considered to be an important factor in this result. Using a 1W diode laser to pump a mode-locked and Q-switched Nd:YLF oscillator peak power levels of 70kW were obtained at a wavelength of 1.047µm. Frequency doubling this output in MgO:LiNbO3 with an energy conversion efficiency of 47% enabled other tunable lasers to be pumped using the second harmonic. Firstly, a synchronously pumped rhodamine 6G dye laser is described which is capable of producing 3.2ps mode-locked pulses in a Q-switched envelope with peak powers of around 10kW. Secondly, a synchronously pumped doubly resonant optical parametric oscillator tunable between 983nm and 1119nm is described. Lastly, a Ti:Sapphire laser producing 400ns pulses with peak powers of 3W at a wavelength of 755nm is demonstrated. This oscillator could be wavelength tuned between 746nm and 838nm. A highly efficient method of frequency doubling C.W. mode-locked lasers was developed. Using an external resonant cavity a frequency doubling energy conversion efficiency of 61% to 532nm was achieved, giving 87mW average power in 8.5ps pulses.
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Bocharova, Irina A. "Laser coulomb explosion imaging of molecular dynamics." Diss., Manhattan, Kan. : Kansas State University, 2009. http://hdl.handle.net/2097/2279.
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Smith, Philip Howard George. "A semi-classical treatment of laser assisted collisions in a soft-photon weak-field regime." Diss., Georgia Institute of Technology, 1991. http://hdl.handle.net/1853/29851.
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MacCormack, Stuart. "Photorefractive techniques for diode laser brightness enhancement." Thesis, University of Southampton, 1991. https://eprints.soton.ac.uk/403318/.
Full textAbstract:
The experimental investigation of a number of techniques using photorefractive materials to increase the spectral and spatial brightness of the output from high power semiconductor laser arrays are discussed. The topics of semiconductor lasers and photorefractive materials are reviewed briefly, and the experimental and theoretical background of array transverse modes and laser array injection locking are discussed fully. Single longitudinal mode operation of a 100mW array coupled to a simple, hemispherical external cavity is reported. A side mode suppression ratio of 14dB was achieved. A spatial brightness enhancement by a factor of 10 is reported for a 1W laser array coupled to a phase conjugate external cavity. A number of techniques for the combination of multiple array outputs into a single beam were investigated. A power of 108mW (220mW, Fresnel corrected) was obtained in a diffraction limited, single mode laser beam using photorefractive two-beam coupling with an injection locked 1W laser array pump. Results on the operation of a reflection geometry phase conjugate master-oscillator, power-amplifier using a 500mW diode laser array are presented. The observation of coherent energy transfer between the outputs from the separate stripes of a laser array is discussed, and an external photorefractive beam combining element is proposed. Phase conjugate fidelity results are presented for a double pass, phase conjugate, multimode fibre amplifier geometry. The experiments suggest that phase conjugate modal unscrambling will still take place in the presence of ~6dB gain. A scheme for a high efficiency, high power multimode fibre amplifier is proposed.
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Yao, Tianfu. "Fibre laser sources with low quantum defect." Thesis, University of Southampton, 2014. https://eprints.soton.ac.uk/372830/.
Full textAbstract:
High power fibre lasers with efficient amplification of optical signals have been widely used for various applications for many years. A great advantage of fibres is their thermal properties, which are so good that fibres are often quoted as being immune to thermal degradation. However, powers keep increasing and the fibre geometry is becoming more similar to their “bulk” (non-waveguiding) counterparts. Thermal problems are severe in bulk lasers, and are, unsurprisingly, becoming more important also for fibres. Heating is inevitable in the laser cycle due to the energy difference(quantum defect) between pump and signal photons. Nevertheless, there is substantial room to reduce the heating by minimising the quantum defect, with pump and signal wavelengths as close as possible. In this thesis, I demonstrate low-quantum-defect fibre amplifiers and lasers based on two different energy conversion processes, i.e., in high-brightness (tandem) pumped ytterbium-doped fibre and in short-wavelength-pumped Raman fibre. The latter approach increases the photon energy relative to the thermal energy and vibrational energy of the host. Firstly, as it comes to tandem-pumping of ytterbium-doped fibre amplifiers, the challenge is to make the pump and signal wavelengths as close as possible, while keeping the signal gain and pump absorption sufficiently high. With the optimum average ytterbium excitation level and high pump brightness, the quantum defect can be as small as 0.6% when pumped at 1030 nm, according to theoretical calculations. Subsequently, an experimental amplifier core-pumped by a single-mode laser source is presented. A 2% quantum defect is reached, with pump and signal wavelengths at 1030 nm and 1050 nm, respectively. The slope efficiency reaches 95% to 96%. Initial investigations show low photodarkening with tandem-pumping, with some dependence on the dependence on ytterbium ions concentration. Secondly, Raman conversion of pulses in a diode-pumped highly nonlinear fibre is studied in a ring-laser cavity configuration. The quantum defect is 3.5% with 806 nm pump and 835 nm Stokes wavelengths. A slope efficiency of 65% is obtained with 600 m long fibre and 100 ns pulse width. Then, I study experimentally and theoretically 975 nm continuous-wave-pumped fibre Raman lasers based on a graded-index and a double-clad fibre. Both lasers emit at 1019 nm (4.3% quantum defect) with improved brightness. A record laser output of 6 W and 19% slope efficiency from the double-clad Raman fibre and 20 W from the graded-index fibre shows further scaling of singlemode power is possible with improved cavity and fibre design.
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Alcock, Ian Peter. "Laser action in neodymium doped silica fibre." Thesis, University of Southampton, 1988. https://eprints.soton.ac.uk/404730/.
Full textAbstract:
This thesis describes an investigation into the suitability of neodymium doped monomode optical fibre as a gain medium for miniature laser systems. Characterisation of the material and parameters required for quantitative analysis of such laser systems are presented in a spectroscopic analysis carried out in the first part of the thesis. Measurements performed in this section also indicate that at room temperature the wide fluorescence bands of the neodymium doped silica fibre are spectrally broadened by a homogeneous process. The behaviour of a longitudinally pumped continuous-wave fibre laser is modelled in the next section followed by the design and realisation of a practical system. Efficiencies of approximately 6% and threshold pump powers of 8-12 mW have been obtained, even under narrow linewidth operation. Tunability over ranges of 45-60nm has also been demonstrated. The thesis is concluded by experiments on pulsed fibre lasers. Q-switching the laser has achieved peak powers of several watts in pulses 180ns wide with good agreement between the results obtained and predicted values. Shorter pulses 450ps wide have been realised by mode-locking a fibre laser. Suggestions for reducing the pulse width further and the effects of material dispersion are also given. Finally modulated pump sources have been investigated and it is shown that synchronous pumping with short pulses has limitations due to dispersion, while resonantly pumping relaxation oscillations is a simple means of obtaining a pulsed output.