Thèses : « Laser for atomic physics »

1

Plimmer, Mark David. « Laser spectroscopy of atomic systems ». Thesis, University of Oxford, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329991.

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2

Tolchard, J. M. « Doppler free laser spectroscopy of atomic hydrogen using pulsed lasers ». Thesis, University of Southampton, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.383868.

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3

Woodman, George Henry. « Precise laser spectroscopy of atomic hydrogen ». Thesis, University of Oxford, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.316894.

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4

Powis, Richard Alexander. « Crossed-beam laser spectroscopy of atomic ruthenium ». Thesis, University of Birmingham, 2013. http://etheses.bham.ac.uk//id/eprint/3959/.

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High resolution crossed-beam laser spectroscopy has been used to measure the isotope shifts and hyperfine parameters of nineteen transitions in atomic ruthenium. These results have been used in conjunction with four other existing transition measurements to determine accurate values for the change in mean-square charge radius between the isotopes of ruthenium. The new charge radii measurements exhibit up to an order of magnitude improvement in accuracy compared to the previously published results. These accurate charge radii systematics in ruthenium provide additional data for the interesting N=60 region of the nuclear chart. The transitions measured have been assessed in terms of their suitability for use in future collinear laser spectroscopy measurements of radioactive ruthenium isotopes. One transition in particular, the 349.8942nm Ocm-1 to 28571.890cm-1 transition, has the potential to be highly efficient.

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5

Sandberg, Jon Carl. « Research toward laser spectroscopy of trapped atomic hydrogen ». Thesis, Massachusetts Institute of Technology, 1993. http://hdl.handle.net/1721.1/12659.

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6

Avila, Carlos A. « Laser cooling of a metastable argon atomic beam ». FIU Digital Commons, 1996. http://digitalcommons.fiu.edu/etd/1342.

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A production of low velocity and monoenergetic atomic beams would increase the resolution in spectroscopic studies and many other experiments in atomic physics. Laser Cooling uses the radiation pressure to decelerate and cool atoms. The effusing from a glow discharge metastable argon atomic beam is affected by a counterpropagating laser light tuned to the cycling transition in argon. The Zeeman shift caused by a spatially varying magnetic field compensates for the changing Doppler shift that takes the atoms out of resonance as they decelerated. Deceleration and velocity bunching of atoms to a final velocity that depends on the detuning of the laser relative to a frequency of the transition have been observed. Time-of-Flight (TOF) spectroscopy is used to examine the velocity distribution of the cooled atomic beam. These TOF studies of the laser cooled atomic beam demonstrate the utility of laser deceleration for atomic-beam "velocity selection".

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7

Gagnon, Justin. « Laser Coulomb explosion imaging of polyatomic molecules ». Thesis, University of Ottawa (Canada), 2006. http://hdl.handle.net/10393/27362.

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Laser technology has steadily evolved over the last 50 years since its invention, and has generated a series of ramifications in experimental science. Particularly, lasers have enabled the creation of the shortest man-made event: a femtosecond pulse of electromagnetic radiation. Due to their unmatched spatial and temporal resolutions, femtosecond pulses have been used in a number of techniques to measure properties of individual molecules. One of these techniques is Coulomb Explosion Imaging (CEI), whose purpose is to retrieve the structure of individual molecules. Unlike frequency domain spectroscopy (which is ill-suited to characterize the structure of large molecules due to their complex spectra) and diffraction techniques (which only work if molecules can be locked into a crystallization pattern), CEI provides a direct measurement of the properties of individual molecules, instead of measuring a sample as a whole. This novel technique was first introduced to study molecular structure by colliding a beam of highly energetic ions onto a thin foil. The version of CEI used in this work uses a beam of neutral molecules and replaces the thin foil with femtosecond optical pulses. The introduction of the laser has brought with it the ability to conduct time-resolved measurements of molecular processes (breaking of molecular bonds, internuclear motion, for example) on a femtosecond time scale using pump-probe techniques in conjunction with CEI. Furthermore, CEI is presently the only technique that can discriminate single molecules based on their handedness. I have conducted a Laser Coulomb Explosion Imaging (LCEI) experiment using dicloromethane as a model polyatomic molecule. In order to perform LCEI, an intense femtosecond laser pulse is used to strip away electrons from a molecule and cause it to explode into smaller fragments. Imaging the molecule is done using data collected from its fragments. Thus, in practice LCEI can be seen as a technique comprising an experimental phase (Coulomb explosion) and an analytical phase (imaging). Dichloromethane was chosen for this study to prepare the techniques that are necessary for future experiments on chiral molecules. The experimental setup used for this instance of LCEI is the PATRICK instrument, a combination of high-end vacuum, electronics and laser equipment, which will also be described herein. The rest of this thesis will focus on the results obtained from the computational tools I developed for imaging the CEI data and obtaining physical properties about the exploded molecules. In doing so I have also obtained the first geometrical reconstructions of five atom molecules from CEI data, which will also be given in this study. Though LCEI is a general technique that can be exploited in a variety of different experiments, this particular project was built around the interest of imaging chiral molecules. Unlike mass, multipole moments, polarizabilities and other "conventional" physical properties of molecules, chirality arises solely from spatial symmetry considerations, making it more elusive. For example, in order to experimentally determine the properties of a molecule in the traditional manner, one proceeds by inferring molecular characteristics from general spectroscopic data pertaining to a sample of molecules. In this manner, molecules are ascribed properties based on statistical measurements done on a population. Although statistical methods are also used to measure the handedness of a sample of molecules, it is understood that these measurements yield information only about the sample, but not the individual molecules themselves. Indeed, chirality is not a property of a type of molecule, but of individual molecules, rendering LCEI very suitable to measure chirality. Accordingly, it is the ultimate goal of this thesis to set the stage for future experiments involving the measurement of the handedness of individual chiral molecules.

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8

Cocolios, Thomas Elias. « Collinear fast-beam laser spectroscopy at ISAC ». Thesis, McGill University, 2005. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=97933.

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Collinear fast-beam laser spectroscopy is a method of studying atomic and ionic hyperfine structure where a particle beam and a laser beam are superposed along the same line. Such a facility exists at ISAC, TRIUMF, Vancouver, BC, and was designed especially for polarising radioactive beams of alkali metals.
In order to produce polarised fluorine for the use in NMR, the hyperfine structure of the 3s 4P 5/2 and 3p 4D 7/2 states has to be known. The hyperfine coefficients for those two levels are measured for the first time to be A = 2645.6(6) MHz and A = 1565.6(4)MHz respectively. The 3p 4D5/2 state is also studied to measure the metastable atom fraction and its hyperfine constant is measured to be A = 1148(5)MHz.
A study of lanthanum ions is also carried out. Spectra for the 6 s2 1S0 to 5 d6p Do13 transition are measured with stable 139La to evaluate the sensitivity of the equipment and with radioactive 139La for preliminary commissioning of the isotope shift study.

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9

Deeny, J. A. « Tunable diode laser spectroscopy ». Thesis, University of Oxford, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.253325.

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10

Hillenbrand, Gerd. « Laser cooling of atoms ». Thesis, University of Oxford, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.259952.

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11

Steane, A. M. « Laser cooling of atoms ». Thesis, University of Oxford, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.315817.

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12

Catala, Juan Carlos. « Laser cooling and trapping of argon metastable atomic beam ». FIU Digital Commons, 1998. http://digitalcommons.fiu.edu/etd/2083.

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The high velocity of free atoms associated with the thermal motion, together with the velocity distribution of atoms has imposed the ultimate limitation on the precision of ultrahigh resolution spectroscopy. A sample consisting of low velocity atoms would provide a substantial improvement in spectroscopy resolution. To overcome the problem of thermal motion, atomic physicists have pursued two goals; first, the reduction of the thermal motion (cooling); and second, the confinement of the atoms by means of electromagnetic fields (trapping). Cooling carried sufficiently far, eliminates the motional problems, whereas trapping allows for long observation times. In this work the laser cooling and trapping of an argon atomic beam will be discussed. The experiments involve a time-of-flight spectroscopy on metastable argon atoms. Laser deceleration or cooling of atoms is achieved by counter propagating a photon against an atomic beam of metastable atoms. The solution to the Doppler shift problem is achieved using spatially varying magnetic field along the beam path to Zeeman shift the atomic resonance frequency so as to keep the atoms in resonance with a fixed frequency cooling laser. For trapping experiments a Magnetooptical trap (MOT) will be used. The MOT is formed by three pairs of counter-propagating laser beams with mutual opposite circular polarization and a frequency tuned slightly below the center of the atomic resonance and superimposed on a magnetic quadrupole field.

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13

Petersen, Michael. « Laser-cooling of Neutral Mercury and Laser-spectroscopy of the 1S0-3P0 optical clock transition ». Phd thesis, Université Pierre et Marie Curie - Paris VI, 2009. http://tel.archives-ouvertes.fr/tel-00405200.

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14

Keating, Christopher M. « Using Strong Laser Fields to Produce Antihydrogen Ions ». Thesis, Portland State University, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10846288.

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We provide estimates of both cross section and rate for the stimulated attachment of a second positron into the (1s² ¹S^e) state of the H¯ ⁺ ion using Ohmura and Ohmura’s (1960 Phys. Rev. 118 154) effective range theory, Reiss’s strong field approximation (1980 Phys. Rev. A 22, 1786), and the principle of detailed balancing. Our motivation for producing H¯⁺ ion include its potential to be used as an intermediate state in bringing antihydrogen to ultra-cold (sub-mK) temperatures required for a variety of studies, which include both spectroscopy and the probing of the gravitational interaction of the anti-atom. We show that both cross section and rate are increased with the use of a resonant laser field.

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15

Barry, John F. « Laser cooling and slowing of a diatomic molecule ». Thesis, Yale University, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3578337.

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Laser cooling and trapping are central to modern atomic physics. It has been roughly three decades since laser cooling techniques produced ultracold atoms, leading to rapid advances in a vast array of fields and a number of Nobel prizes. Prior to the work presented in this thesis, laser cooling had not yet been extended to molecules because of their complex internal structure. However, this complexity makes molecules potentially useful for a wide range of applications. The first direct laser cooling of a molecule and further results we present here provide a new route to ultracold temperatures for molecules. In particular, these methods bridge the gap between ultracold temperatures and the approximately 1 kelvin temperatures attainable with directly cooled molecules (e.g. with cryogenic buffer gas cooling or decelerated supersonic beams). Using the carefully chosen molecule strontium monofluoride (SrF), decays to unwanted vibrational states are suppressed. Driving a transition with rotational quantum number R=1 to an excited state with R'=0 eliminates decays to unwanted rotational states. The dark ground-state Zeeman sublevels present in this specific scheme are remixed via a static magnetic field. Using three lasers for this scheme, a given molecule should undergo an average of approximately 100,000 photon absorption/emission cycles before being lost via unwanted decays. This number of cycles should be sufficient to load a magneto-optical trap (MOT) of molecules. In this thesis, we demonstrate transverse cooling of an SrF beam, in both Doppler and a Sisyphus-type cooling regimes. We also realize longitudinal slowing of an SrF beam. Finally, we detail current progress towards trapping SrF in a MOT. Ultimately, this technique should enable the production of large samples of molecules at ultracold temperatures for molecules chemically distinct from competing methods.

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16

Levick, Andrew Philip. « Laser photofragment spectroscopy of molecular ions ». Thesis, University of Nottingham, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.277619.

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17

England, J. G. « Laser resonance spectroscopy of samarium isotopes ». Thesis, University of Manchester, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.374792.

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18

Hamilton, J. H. « Photoacoustic spectroscopy of neodymium-doped laser materials ». Thesis, Queen's University Belfast, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.374196.

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19

Chen, Hongxin. « Electromagnetically induced transparency in laser-cooled rubidium ». Thesis, Open University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.265348.

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20

Roberts, Gareth. « Collisional processes of laser-excited alkaline earth atoms ». Thesis, University of Cambridge, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.346405.

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21

Clark, Eugene Laurence. « Measurements of energetic particles from ultraintense laser plasma interactions ». Thesis, Imperial College London, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.271738.

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22

Boshier, M. G. « Precise laser spectroscopy of the hydrogen 1S-2S transition ». Thesis, University of Oxford, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.233478.

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23

Walmsley, J. M. « High resolution laser photofragment spectroscopy of diatomic molecular ions ». Thesis, University of Nottingham, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.384337.

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24

Anacona, J. R. « Far infrared and mid infrared laser spectroscopy of free radicals ». Thesis, University of Cambridge, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.304717.

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25

Smith, Andrew Michael. « Theoretical studies of long-range collisions between laser cooled atoms ». Thesis, University of Oxford, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.315816.

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26

Cross, Gillian M. « The multiphoton multiple ionization of molecules in intense laser fields ». Thesis, University of Reading, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.283758.

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27

Law, D. W. « The laser induced isomerisation and photoacoustic spectroscopy of small molecules ». Thesis, University of Reading, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.234897.

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28

Rothwell, W. J. M. « Infrared diode laser spectroscopy of free radicals and molecular ions ». Thesis, University of Cambridge, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.355508.

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29

McKendrick, Colin Bruce. « UV laser multiphoton dissociation studies of H2O, NO2 and H2O2 ». Thesis, University of Edinburgh, 1986. http://hdl.handle.net/1842/12630.

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30

Blease, Trevor Graham. « Laser multiphoton ionization spectroscopy and analysis of the xylene isomers ». Thesis, University of Edinburgh, 1985. http://hdl.handle.net/1842/14139.

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31

Lignier, Hans. « Etude de la localisation dynamique avec des atomes refroidis par laser ». Phd thesis, Université des Sciences et Technologie de Lille - Lille I, 2005. http://tel.archives-ouvertes.fr/tel-00011644.

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Le chaos quantique désigne l'étude de systèmes dont le prolongement classique est chaotique. Le modèle du pendule pulsé, qui en est un exemple paradigmatique, est réalisé expérimentalement en plaçant un échantillon d'atomes refroidis (MOT) dans une onde stationnaire pulsée formée par un faisceau laser retro-reflechi. L'étude de la dynamique s'appuie sur la mesure de la distribution d'impulsions des atomes.
Après avoir retrouvé expérimentalement le phénomène quantique de localisation dynamique, lié au caractère périodique de la séquence de pulses, la destruction de ce phénomène (délocalisation dynamique) par l'utilisation de séquences superposant deux séries de pulses de période (séquence bicolore) est étudiée puis expliquée par un modèle théorique. Cette analyse suggère que la délocalisation est, dans ce contexte, réversible. Il est ainsi montré expérimentalement qu'une séquence bicolore inversée conduit une délocalisation suivie d'une relocalisation.

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32

Nacher, Pierre-Jean. « Observations d'ondes de spin dans un gaz d'hélium-3 polarisé par pompage optique laser ». Phd thesis, Université Pierre et Marie Curie - Paris VI, 1985. http://tel.archives-ouvertes.fr/tel-00011855.

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33

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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34

Girard, Bertrand. « Etude de la collision réactive I2+F-F+I par fluorescence induite par laser ». Phd thesis, Université Pierre et Marie Curie - Paris VI, 1987. http://tel.archives-ouvertes.fr/tel-00010493.

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Les collisions réactives entre un atome et une molécule représentent l'acte chimique élémentaire le plus simple. C'est donc à travers l'étude de ces collisions que l'on peut atteindre une compréhension fondamentale de la réaction chimique. Une technique particulièrement efficace pour ces études est la détection par fluorescence induite par laser des produits moléculaires de réaction. Cette technique de détection, sélective en état interne, permet de connaître la distribution du produit moléculaire sur les états internes, et même de mesurer pour chacun de ces états la section efficace différentielle, la vitesse étant déterminée par effet Doppler. Nous nous sommes intéressé à la collision F + I2 —-> I F + I que nous avons étudiée dans une expérience de jets croisés. La section efficace de réaction est importante et la molécule IF est facilement détectable par fluorescence induite par laser grâce à la transition (B<-X) qui intense et située dans le visible. Nous avons ainsi pu travailler avec des lasers à colorants continus monomodes. La saturation du processus d'excitation laser de cette transition a été soigneusement étudiée, de manière théorique et expérimentale. Cette étude, ainsi qu'une analyse détaillée de la spectroscopie de la transition (B<-X) nous a permis de déduire des intensités des raies de fluorescence les populations des différents niveaux rovibrationnels peuplés de l'état X, avec la plus grande cohérence interne possible. D'une part nous avons ainsi pu établir une cartographie détaillée de la distribution rotationnelle des niveaux vibrationnels v = 8 à 20 de l'état X de IF. Celle-ci s'étend jusqu'à la limite d'énergie disponible dans tous ces niveaux. Ces distributions rotationnelles présentent un aspect bimodal qui implique la coexistence de deux chemins réactionnels microscopiques différents. Cette bimodalité a été observée récemment dans une autre, étude expérimentale de cette réaction (où IF est détecté de manière non sélective, mais où sa vitesse de recul est mesurée) et prévue dans une simulation numérique de la réaction. D'autre part, nous avons montré que l'important signal observé dans des expériences antérieures sur le niveau v=0 était un artefact provoqué par des réactions de surface. Enfin, des mesures préliminaires par effet Doppler de la section efficace différentielle sont présentées. En conclusion, de nombreux résultats nouveaux onc été obtenus sur cette collision reactive. Nous avons montré, par exemple, que l'utilisation soignée; de la fluorescence induite par laser mène à des mesures précises de la distribution des molécules sur leurs états internes. La connaissance de cette réaction a ainsi pu être considérablement approfondie: celle-ci est sans doute actuellement l'une des collisions réactives les mieux décrites expérimentalement.

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35

Madden, Colette Sarah. « An investigation of InXe interaction potentials using laser induced fluorescence techniques ». Thesis, Queen's University Belfast, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.334482.

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36

De, Echaniz SebastiaÌn R. « Coherence effects in three and four level laser cooled rubidium systems ». Thesis, Open University, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.250490.

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37

Pardon, Patrick Roger. « A study of small molecules by molecular beam and laser techniques ». Thesis, University of Southampton, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.292464.

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38

Woods, Jonathan. « A mode-locked diode laser frequency comb for ultracold atomic physics experiments ». Thesis, University of Southampton, 2016. https://eprints.soton.ac.uk/388517/.

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This thesis is concerned with the development and characterisation of an actively mode locked diode laser system for the provision of a stable optical frequency comb spanning approximately 1 nm around the D2 spectroscopic line of Rubidium. Through large signal sinusoidal modulation of the laser DC injection current at around 3 GHz, Gaussian pulses of 21 ps are achieved with an associated spectral bandwidth in excess of 1 nm, generating pulses of optimal time-bandwidth product 13. An in-house built air-bearing Michelson interferometer is used to confirm the comb-like structure of the optical emission and a modulation frequency detuning range of 10 MHz is determined. Through a proof of principle investigation of CW injection locking of the frequency comb, phase coherence of the CW master laser with the modes of the frequency comb is demonstrated over at least 36 GHz. Via CW injection locking, sidemode suppression of 20.6 dB is achieved resulting in an 18% rise in the pulse temporal width and a concomitant reduction in the time-bandwidth product to 1.44, as well as a power dependant phase locking detuning range of up to 370 MHz. In the closing chapters, two CW lasers are shown to be stabilised to the frequency comb via Optical Phase-Locked Loops, a temperature stabilised fibre Mach-Zehnder interferometer is demonstrated for carrier frequency removal from a phase modulated laser, and a novel intra-cavity trace water vapour detection method is introduced.

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39

Harris, Peter Ronald. « Laser desorption from a room temperature ionic liquid ». W&M ScholarWorks, 2009. https://scholarworks.wm.edu/etd/1539623542.

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We report laser desorption from a Room Temperature Ionic Liquid (RTIL) as a novel source for time of flight mass spectrometry. We use the 2nd harmonic of an Nd:YAG laser to deposit intensities of 1-50 MW/cm2 via backside illumination onto our RTIL desorption sample. A microstructured metal grid situated on top of a glass microscope slide coated with RTIL serves as our desorption sample. The RTIL we use, 1-Butyl, 3-Methylimidazolium Hexafluorophosphate, remains liquid at pressures below 10-8 torr. The use of liquid desorption sample allows for improved surface conditions, homogeneity and sample life as compared to Matrix Assisted Laser Desorption Ionization (MALDI) techniques. Our desorption technique is also unique as it allows the study of both multiphoton and acoustic desorption processes within the same time of flight spectra. Our technique yields intrinsically high resolution, low noise data. We observe differences between ion species in their preference for desorption by a particular desorption method. Specifically, we observe desorption solely by acoustic means of an entire RTIL molecule adducted with an RTIL cation. Finally, we report the applicability of this technique for the desorption of biomolecules.

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40

Schef, Peter. « Weak Atomic Interactions ». Doctoral thesis, Stockholm : Physics Department, Stockholm University, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-1064.

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41

Renzoni, Ferruccio. « Habilitation à diriger des recherches ». Habilitation à diriger des recherches, Université Pierre et Marie Curie - Paris VI, 2003. http://tel.archives-ouvertes.fr/tel-00003299.

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Ce mémoire d'habilitation présente mes travaux de recherche, du
début de ma thèse jusqu'à présent. Le manuscrit est divisé en deux parties. La première présente mes travaux de thèse et une partie des résultats obtenus pendant mon séjour post-doctoral à l'Université de Hambourg. En particulier, cette partie contient
les résultats de ma recherche sur le rôle des cohérences à basse
fréquence en spectroscopie laser.
Les sujets abordés ont été le piégeage cohérent de population, les résonances brillantes, la préparation et la manipulation d'états quantiques en utilisant des états noirs dépendant du temps, et l'étude des effets de cohérence à basse fréquence dans la spectroscopie de transport des boîtes quantiques couplées par effet tunnel.

La deuxième partie de ce mémoire présente mon travail de recherche
sur les réseaux d'atomes froids. Le sujet principal de cette recherche a été la dynamique des atomes dans les réseaux optiques. Le mouvement diffusif des atomes, la relaxation de leur énergie cinétique, et leurs modes de propagation ont été étudiés. Les progrès faits dans la compréhension de la dynamique atomique dans les réseaux optiques ont été ensuite exploités pour expliquer l'origine de la résonance Rayleigh dans le spectre d'absorption des atomes piégés dans le réseau. De plus, nous avons utilisé les réseaux optiques comme système modèle pour des phènomènes de physique non-linéaire. Nous avons ainsi étudié la résonance stochastique dans un réseau périodique, et la diffusion dirigée dans un potentiel symétrique.

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42

Chae, Eunmi. « Laser Slowing of CaF Molecules and Progress Towards a Dual-MOT for Li and CaF ». Thesis, Harvard University, 2016. http://nrs.harvard.edu/urn-3:HUL.InstRepos:26718753.

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Diatomic molecules are considered good candidates for the study of strongly correlated systems and precision measurement searches due to their combination of complex internal states and strong long-range interactions. Cooling molecules down to ultracold temperatures is often a necessary step for fully utilizing the power of the molecule. This requires a trap for molecules and the ability to cool molecules to the mK regime and below. A magneto-optical trap (MOT) is a good tool for achieving mK temperatures. However, extra care is needed for molecules to form the necessary quasi-closed cycling transitions due to molecule's complicated energy structure. In our work with CaF, we use two repump lasers to block vibrational leakage and selection rules for the rotational degree of freedom to achieve about 10^{5} photon cycles. The two-stage buffer gas beam source is a general method to generate a cold and slow beam of molecules with a forward velocity of about 50 m/s. The compatibility of the buffer-gas source with a MOT is studied and we confirm that such beams can be nicely compatible with MOTs using various atomic species. In order to load molecules into a MOT from even such a slow beam, additional slowing is required due to the low capture velocity of a molecular MOT (< 10 m/s). We apply a frequency-broadened “white-light” slowing on CaF from a two-stage source, demonstrating slowing of CaF below 10 m/s. An AC MOT, which provides active remixing of dark substates, is also developed and Li atoms are slowed and trapped. These are crucial ingredients for co-trapping CaF molecules and Li atoms and study their collisional properties, which would lead to sympathetic cooling of molecules down to ultracold temperatures. The achievement of slowing and development of this system allowed for the detailed study of the CaF laser cooling system, as well as physical processes involved with AC MOTs and the proposed MOT for CaF. Crucial knowledge of this archetypal system provides significant progress toward manipulation and control of molecules similar to what has been achieved with atoms and what is necessary for searches for new physics with ultracold molecules.
Physics

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43

Gurell, Jonas. « High Resolution Spectroscopy of Singly Charged Ions : Applications of Laser and Fourier Transform Techniques ». Doctoral thesis, Stockholms universitet, Fysikum, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-42627.

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This thesis presents measurements of fundamental properties of singly charged ionic systems including spectral wavelengths, lifetimes of excited states and branching fractions with the main focus on time resolved laser spectroscopy of stored ions providing lifetime measurements of metastable states. The results of these measurements have been used to determine energy levels and transition probabilities of the studied systems. The included experimental data are compared with results from calculations which provides evaluations of different theoretical models. The presented results have been applied by others to the field of atomic astrophysics in order to deduce electron densities and elemental abundances in ejecta of the supermassive star eta Carinae and have also been followed by additional work of theoreticians interested in comparisons with laboratory data. The thesis is a result of several collaborations in which Stockholm University has been providing lifetime measurements of metastable states, Lund Observatory and the National Institute of Standards and Technology have been providing wavelength and branching fraction measurements, Lund Laser Centre has been providing lifetime measurements of short-lived states and calculations have been performed by theoretical physicists from Université de Mons-Hainaut, Université de Liège, Queen's University of Belfast and Laboratoire Aimé Cotton.

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Kaminski, Lech. « The spectroscopic study of simple polyatomic molecules by synchrotron and laser irradiation ». Thesis, University College London (University of London), 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.248127.

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Ning, Ya Nong. « A study of optical fibre interferometric systems using multimode laser diode light sources ». Thesis, City University London, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.316037.

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Coudreau, Thomas. « Réduction du bruit et tomographie quantique d'un faisceau laser interagissant avec des atomes froids : théorie et expériences ». Phd thesis, Université Pierre et Marie Curie - Paris VI, 1997. http://tel.archives-ouvertes.fr/tel-00011915.

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Nous avons utilisé un nuage d'atomes refroidis par laser comme milieu non linéaire pour réduire les fluctuations quantiques d'un faisceau laser. Le nuage atomique, produit par un piège magnéto-optique en fonctionnement continu, est placé dans une cavité optique. Les fluctuations du faisceau sonde réfléchi par la cavité sont mesurées à l'aide d'une détection homodyne. Une réduction de bruit en quadrature de 15% a été obtenue pendant plusieurs secondes. Sur le plan théorique, nous avons utilisé la méthode des forces de Langevin pour calculer le spectre des fluctuations avec un modèle atomique à trois niveaux. Ce modèle permet de prendre en compte l'effet parasite des faisceaux pièges et de repompage. Il est en bon accord avec les résultats expérimentaux. Par ailleurs, nous avons utilisé la méthode de tomographie quantique pour mesurer la fonction de Wigner du champ réfléchi par la cavité. Cette fonction permet de caractériser tous les moments statistiques des fluctuations. Cette mesure est la première mesure de la fonction de Wigner d'un état produit par interaction avec un milieu atomique. Cette méthode a permis de mettre en évidence une statistique gaussienne en bon accord avec les prédictions théoriques.

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Nunnenkamp, Andreas. « Strong correlations in ultracold atomic gases ». Thesis, University of Oxford, 2008. http://ora.ox.ac.uk/objects/uuid:6e09e9d3-f5cd-4580-a667-6599203162e2.

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In this thesis we investigate strongly-correlated states of ultracold bosonic atoms in rotating ring lattices and arrays of double-well potentials. In the first part of the thesis, we study the tunneling dynamics of ultracold bosons in double-well potentials. In the non-interacting limit single-particle transitions dominate, while in the interaction-dominated regime correlated tunneling of all particles prevails. At intermediate times of the many-particle flopping process correlated states occur, but the timescales of these processes increase dramatically with the number of particles. Using an array of double-well potentials, a large number of such few-particle superposition states can be produced in parallel. In the second part of the thesis, we study the effects of rotation on ultracold bosons confined to one-dimensional ring lattices. We find that at commensurate filling there exists a critical rotation frequency, at which the ground state of the weakly-interacting gas is fragmented into a macroscopic superposition of different quasi-momentum states. We demonstrate that the generation of such superposition states using slightly non-uniform ring lattices has several practical advantages. Moreover, we show that different quasi-momentum states can be distinguished in time-of-flight absorption imaging and propose to probe correlations via the many-body oscillations induced by a sudden change in the rotation frequency. Finally, we compare these macroscopic superposition states to those occurring in superconducting quantum interference devices. In the third part of the thesis, we demonstrate the creation of entangled states with ultracold bosonic atoms by dynamical manipulation of the shape of the lattice potential. To this end, we consider an optical superlattice that allows both the splitting of each site into a double-well potential and the variation of the height of the potential barrier between the sites. We show how to use this array of double-well potentials to perform entangling operations between neighboring qubits encoded on the Zeeman levels of the atoms. As one possible application, we present a method of realizing a resource state for measurement-based quantum computation via Bell-pair measurements. In the final part of the thesis, we study ultracold bosons on a two-dimensional square lattice in the presence of an effective magnetic field and point out a couple of features this system has in common with ultracold bosons in one-dimensional rotating ring lattices.

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Heijkenskjöld, Filip. « Experimental Techniques for Studies in Atomic & ; Molecular Physics ». Doctoral thesis, Uppsala University, Department of Physics and Materials Science, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-9295.

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This thesis is based on a selection of six different experimental techniques used for studies in atomic and molecular physics. The techniques analysed in the thesis are compared to find similarities in strategies and ways to avoid sources of error.

Paper 1 deals with collision based spectroscopy with 60 keV Xe6+ ions on sodium and argon gas targets. Information on energy of Rydberg states in Xe5+ is unveiled by optical spectroscopy in the wavelength range from vacuum ultraviolet (VUV) to visible. In paper 2, the fast ion-beam laser spectroscopy (FIBLAS) is adapted for measuring hyperfine structure of barium isotopes in an isotopically pure ion-beam. This techniques involves changing the isotope during the measurement to minimize sources of error in measurement and enhance the signal from lesser abundant isotopes. The FIBLAS technique is used in paper 3 to study samarium ions. The ions are optically pumped and the recorded optical nutation is used to measure transition probabilities. This technique eludes the difficulties inherent in relative intensity measurements of all the radiative transitions from an excited state. In Paper 4, optical emission spectroscopy is used in the VUV region to study noble gas mixture discharges. The source of the emission bands near the resonance lines of krypton and xenon are found to be heteronuclear dimers. In paper 5, radiation from a pulsed argon plasma with admixture of nitrogen is studied with time resolved spectroscopy in the VUV and ultraviolet wavelength ranges to investigate the mechanism of energy transport. A metastable state of atomic argon is found to be an important source of energy to many radiative processes. In Paper 6, photoelectron spectroscopy (PES) on thiophene, on 3-bromothiophene and on 3,4-dibromothiophene using time-of-flight photoelectron-photoelectron coincidence technique and conventional PES to investigate the onset of double ionisation compared to the onset of single ionisation in molecules.

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Kling, Nora G. « Controlling the dynamics of electrons and nuclei in ultrafast strong laser fields ». Diss., Kansas State University, 2013. http://hdl.handle.net/2097/16821.

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Doctor of Philosophy
Department of Physics
Itzik Ben-Itzhak
One ultimate goal of ultrafast, strong- field laser science is to coherently control chemical reactions. Present laser technology allows for the production of intense (>10[superscript]13 W/cm[superscript]2), ultrashort ( 5 fs), carrier-envelope phase-stabilized pulses. By knowing the electric field waveform, sub-cycle resolution on the order of 100's of attoseconds (1 as=10[superscript]-18 s) can be reached -- the timescale for electron motion. Meanwhile, the laser field strengths are comparable to that which binds electrons to atoms or molecules. In this intense-field ultrashort-pulse regime one can both measure and manipulate dynamics of strong-field, quantum-mechanical processes in atoms and molecules. Despite much progress in the technology, typical durations for which lasers can be reliably locked to a specific carrier-envelope phase ranges from a few minutes to a few hours. Experiments investigating carrier-envelope phase effects that have necessarily long data acquisition times, such as those requiring coincidence between fragments originating from the same atom or molecule, are thus challenging and uncommon. Therefore, we combined the new technology for measuring the carrier-envelope phase of each and every laser shot with other single-shot coincidence three-dimensional momentum imaging techniques to alleviate the need for carrier-envelope phase stabilized laser pulses. Using phase-tagged coincidence techniques, several targets and laser-induced processes were studied. One particular highlight uses this method to study the recollision process of non-sequential double ionization of argon. By measuring the momentum of the two electrons emitted in the process, we could study their energy sharing. Furthermore, by selecting certain carrier-envelope phase values, and therefore laser pulses with a particular waveform, events with single recollision could be isolated and further analyzed. Another highlight is our studies of carrier-envelope phase effects in the dissociation of the benchmark H[subscript]2[superscript[+] ion beam. Aided by near-exact quantum mechanical calculations, we could identify interfering pathways which lead to the observed spatial asymmetry. These and other similar experiments are described in this thesis as significant steps toward their ultimate control.

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Fletcher, Aaron Thomas. « A Study of Alkali-Resistant Materials for Use in Atomic Physics Based Systems ». Wright State University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=wright1506342433540236.

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