No description available.

The region surrounding the Z = 82 major-shell closure has exhibited the strongest known manifestation of shape coexistence, to date. Due to this, the nuclides that inhabit this region have been subject to extensive decay- and laser-spectroscopy studies. In this work, the results from two investigations performed at the CERN, ISOLDE facility will be presented: the first, an α-decay study of two states in 178 Au, and the second, an in-source laser-spectroscopy experiment performed on a long chain of At isotopes. Two states, a low-spin ground state, and a high-spin isomer, were directly identified in 178 Au (Z = 79, N = 99) for the first time. Due to the highly selective resonant laser-ionisation method, it was possible to produce isomerically pure beams of the ground and isomeric states. These beams were then ustilised in order to perform dedicated α-decay studies upon the two states. Successful measurements were made for the half-lives, branching ratios, and decay patterns of 178g,mAu. The first ever laser-spectroscopy measurements were performed on a long chain of At isotopes, using the in-source resonant ionisation technique. The isotope shifts and hyperfine structures of long-lived states in 195−211,217−219At were measured. From these, values for the corresponding changes in mean-squared charge radius, and magnetic dipole moments were extracted. The charge-radii of the neutron-deficient At isotopes display a strong onset of deformation, as the neutron number approaches the N = 104 midshell. The observed onset is more pronounced than the one seen in the Po isotopes, which is noted to be exceptionally strong. Based on the extracted charge-radii and magnetic moments, cases for shape coexistence were identified in 195,197,199At. In the case of the neutron-rich At isotopes, an inversion of the normal odd-even-staggering has given evidence for the presence of octupole collectivity.

A polarization-dependent modulation device, the rough-surfaced retardation plate is proposed as a depolarizer in this thesis. It realizes the decorrelation to the incident field like the traditional diffuser, and scrambles the polarization state simultaneously like a depolarizer. For various surface-roughness plate models, the comprehensive and rigorous analysis of its modulation behaviour is achieved. On the basis of the 2×2 beam coherence-polarization matrix, the statistical properties of the modulated field are examined to reveal the dependence on the surface structure of the rough-surfaced retardation plate. Within the framework of the Complex ABCD matrix theory for general optical propagation systems under the paraxial approximation, the propagated polarization speckle on observation plane over a distance is studied. The analytical expression of its beam coherence-polarization matrix illustrating the change of degree of coherence and polarization on propagation is obtained too. It is approved that the depolarizer provides a flexible and simple method to generate the randomly de-correlated and depolarized speckle with spatially varying polarization states. In addition, the dynamic properties of polarization speckle are analysed to reveal the shape and the motion features of the polarization speckles on the observation plane. At last, a depolarizer consisting of random polarizer cells is introduced to generate polarization speckle as an attempt for a potential method different from the common phase modulation screens.

No description available.

No description available.

With the advent of techniques such as Stimulated Emission Depletion Microscopy (STED) and light sheet microscopy, the generation of specialised light beams has become an exciting field. However, while very effective methods of generating such beams exist, the components necessary to do so are generally large and cumbersome. Metasurfaces promise the replacement of these traditional bulky optical elements with sub-wavelength thick and flat alternatives, paving the way for integration into microscale form factors. Metasurfaces commonly use a distribution of nanoscale resonant elements to engineer a phase plate that shapes light through the Huygens' principle, allowing them to mimic and improve upon traditional optics. Initially, plasmonic resonant elements were explored by the community, but their dissipative losses have severely limited the efficiency of these devices. Here I discuss my work on the development of dielectric sub-wavelength grating based metasurfaces. Four types of metasurface, each using a different manifestation of grating physics are explored: direct phase, polarisation conversion, geometric phase, and active metasurfaces. I show that these different types of metasurface together allow the shaping of a wide variety of beams under a large range of different conditions, while retaining efficiencies on the order of 80-90%. Examples of the beam shapes explored include focused beams, vortex beams, Bessel beams and cylindrical vector beams. The development of high efficiency dielectric metasurfaces brings ultrathin optics closer to practical applications. Their materials and sizes facilitate the integration into previously unavailable form factors, including applications in microfluidics.

Since the birth of mode-locking the temporal duration of optical pulses has radically diminished. In parallel to this, bandwidths have grown so large that almost entire frequency octaves are present in today’s few-cycle pulses. This thesis investigates the character of ultra-wideband pulses in nonlinear environments. Because of the growth in optical bandwidths, traditional definitions and propagation models break down, requiring newer more accurate numerical techniques. A novel approach capturing the uni-directionality of pulses is presented in the form of Gvariables by combining the electric and magnetic field descriptions. These G-variables have the advantage of both an accurate spectral representation and a reduced computational overhead, making them significantly more efficient than existing direct Maxwell solvers. Such approaches are particularly important where large propagation distances and/or transverse dimensions are concerned. Pseudo-spectral techniques play a key role in the success of these wideband models enabling sub-cycle dynamics to be studied. One such phenomenon is Carrier Wave Shocking (CWS), where the optical carrier undergoes self-steepening in the presence of third-order nonlinearity. This process is carefully studied, focussing on the effect of dispersion and the feasibility of its physical realisation. The process is then generalised to arbitrary nonlinear order, where the quadratic form finds potential applications in High Harmonic Generation (HHG). Shock detection schemes are also developed, and agree with analytical solutions in the dispersionless regime. To fully characterise few-cycle pulses, the absolute Carrier Envelope Phase (CEP) must be known. A novel 0 − f self-referencing scheme relying on wideband interference is investigated. By applying robust frequency domain definitions a proposal is made to convert this scheme into one that determines absolute CEP. The scheme maps the level of spectral interference to absolute CEP using numerical simulations.

This thesis reports a measurement of the break-up reaction \(^1\)\(^2\)C(\(^4\)He, \(^1\)\(^2\)C*)\(^4\)He performed at the Birmingham MC40 cyclotron facility at a beam energy of 40 MeV. An array of four double-sided silicon-strip detectors was used to detect the final-state products of the reaction. Results from previous measurements of this reaction have shown that various excited states in \(^1\)\(^2\)C can be populated. In the present study the 13.3 MeV and the 22.4 MeV resonances were, in particular, populated. The latter has been seen for the first time. The analysis for both resonances was performed using the angular correlations technique from which their spin and parity were determined with values of J\(^p\)=4\(^+\) and J\(^p\)=5\(^-\), respectively. Monte-Carlo simulations were performed both before and after the experiment in order to have the optimal detector-array efficiency and normalise the results of the angular correlations analysis. The results have been compared to predictions of the algebraic cluster model, for which the J\(^p\)=4\(^+\) is thought to be related to a rotational band based on the Hoyle state and the J\(^p\)=5\(^-\) resonance is part of the ground-state band. This latter state provides strong evidence for triangular D\(_3\)\(_h\) symmetry corresponding to an equilateral triangle structure, observed here for the first time in a nucleus.

A number of inner-complex compounds of beryllium, aluminium, iron, copper and nickel have been prepared, and measurements of the molecular polarisation have been made on those which were sufficiently soluble in either benzene or dioxan. A heterodyne beat apparatus was used for dielectric constant measurements. The appropriate molecular refractions have been either measured or calculated, and, on the assumption that the molecules are symmetrical, the atomic polarisations have been estimated. These values of the atomic polarisations are discussed in relation to the force constants for the bending vibrations of the chelate rings and the effective dipole moments of the rings. It was found that the large atomic polarisations observed by previous workers for the acetylacetonates are apparently general for all inner-complex compounds in which the chelate ring contains six atoms. Exceptions may occur when the ring is held rigidly by some means, as in the salicylaldoxime complexes, where hydrogen bonding between the two oxime residues has been postulated to explain their unusually low atomic polarisations. For the other six-membered ring complexes, atomic polarisation values of between 29 and 67 c.c. were found for complexes containing two chelate rings in the molecule, and between 45 and 94 c.c. when three chelate rings are present, the variations being due to changes in the ring moment and the force constant. It was found that the force constants were considerably affected by changes in the strain of the chelate ring, since an increase in the strain of the ring increased its rigidity. Complexes of copper and nickel which contained five-membered rings have quite small atomic polarisations, this being attributed to the large force constants for the vibration of the rings which in these compounds are greatly strained.

Les réseaux optiques sont des structures créées par l'interférence de faisceaux lasers, qui permettent de piéger et d'ordonner les atomes froids. Ils sont devenus un système modèle pour divers domaines de la physique, car il est possible d'imiter d'autres systèmes en changeant la géométrie et les paramètres du réseau. Ces caractéristiques sont faciles à modifier expérimentalement, de sorte qu'il est possible d'obtenir des réseaux optiques conservatifs. Dans cette thèse, nous étudions la dynamique d'un atome piégé dans un réseau optique conservatif à 2D. Cette dynamique dépend des paramètres du réseau, et elle est souvent complexe. Cette thèse se situe donc à l'interface entre le domaine des atomes froids et celui de la dynamique non linéaire. L'étude de la dynamique dans le réseau optique nécessite d'abord un traitement dans la limite classique. Nous examinons premièrement les solutions des équations du mouvement obtenues par intégration numérique, pour les différentes configurations du système. Elles montrent une grande variété de régimes dynamiques possibles. Parmi ces régimes, on observe des phénomènes de synchronisation menant à un mouvement périodique accroché en fréquence. La synchronisation semble inhiber le chaos dans le système. Les principales solutions obtenues numériquement sont aussi étudiées analytiquement. Cette approche permet d'obtenir une description du mouvement pour les différents régimes dynamiques observés. Tous ces régimes sont faciles à reproduire expérimentalement et l'influence de la synchronisation sur l'apparition du chaos mérite d'être étudiée. D'autre part, cette analyse classique du système ouvre la voie à l'étude de sa limite quantique. / Optical lattices are structures created by the interference of laser beams, which make it possible to trap and arrange cold atoms. They have become a model system for several domains in physics, because it is possible to simulate other systems by changing the lattice geometry and its parameters. These characteristics are easy to modify experimentally. In particular, it is possible to obtain conservative optical lattices. In this thesis, we study the dynamics of an atom trapped in a 2D conservative optical lattice. The dynamics of the atom depends on the parameters of the lattice, and it is often complex. In consequence, this thesis is at the interface between the domains of cold atoms and non-linear dynamics. The study of the dynamics in the optical lattice needs to be done firstly in the classical limit. We examine in the first place the solutions to the movement equations obtained by numerical integration, for the different configurations of the system. They show a big variety of possible dynamical regimes. Amongst these regimes we find synchronization phenomena leading to a periodic movement locked in frequency. Synchronization seems to inhibit chaos in the system. The main solutions obtained numerically are also studied analytically. This approach allows us to obtain a description of the movement for the different dynamical regimes observed. All these regimes are easy to reproduce experimentally and the influence of synchronization on the existence of chaos needs to be studied. Additionally, this classical analysis serves as a basis for studying the system in the quantum limit.