Studies on the interaction of two level atoms with quantized electromagnetic field

The present study described about the interaction of a two level atom and squeezed field with time varying frequency. By applying a sinusoidal variation in the frequency of the field, the randomness in population inversion is reduced and the collapses and periodic revivals are regained. Quantum optics is an emerging field in physics which mainly deals with the interaction of atoms with quantised electromagnetic fields. Jaynes-Cummings Model (JCM) is a key model among them, which describes the interaction between a two level atom and a single mode radiation field. Here the study begins with a brief history of light, atom and their interactions. Also discussed the interaction between atoms and electromagnetic fields. The study suggest a method to manipulate the population inversion due to interaction and control the randomness in it, by applying a time dependence on the frequency of the interacting squeezed field.The change in behaviour of the population inversion due to the presence of a phase factor in the applied frequency variation is explained here.This study also describes the interaction between two level atom and electromagnetic field in nonlinear Kerr medium. It deals with atomic and field state evolution in a coupled cavity system. Our results suggest a new method to control and manipulate the population of states in two level atom radiation interaction,which is very essential for quantum information processing.We have also studied the variation of atomic population inversion with time, when a two level atom interacts with light field, where the light field has a sinusoidal frequency variation with a constant phase. In both coherent field and squeezed field cases, the population inversion variation is completely different from the phase zero frequency modulation case. It is observed that in the presence of a non zero phase φ, the population inversion oscillates sinusoidally.Also the collapses and revivals gradually disappears when φ increases from 0 to π/2. When φ = π/2 the evolution of population inversion is identical to the case when a two level atom interacts with a Fock state. Thus, by applying a phase shifted frequency modulation one can induce sinusoidal oscillations of atomic inversion in linear medium, those normally observed in Kerr medium. We noticed that the entanglement between the atom and field can be controlled by varying the period of the field frequency fluctuations. The system has been solved numerically and the behaviour of it for different initial conditions and different susceptibility values are analysed. It is observed that, for weak cavity coupling the effect of susceptibility is minimal. In cases of strong cavity coupling, susceptibility factor modifies the nature in which the probability oscillates with time. Effect of susceptibility on probability of states is closely related to the initial state of the system.

Synthesis and Photoluminescence Properties of Novel Red Phosphors for White Light Emitting Diode Applications

Several series of Eu3+ based red emitting phosphor materials were synthesized using solid state reaction route and their properties were characterized. The present studies primarily investigated the photoluminescence properties of Eu3+ in a family of closely related host structure with a general formula Ln3MO7. The results presented in the previous chapters throws light to a basic understanding of the structure, phase formation and the photoluminescence properties of these compounds and their co-relations. The variation in the Eu3+ luminescence properties with different M cations was studied in Gd3-xMO7 (M = Nb, Sb, Ta) system.More ordering in the host lattice and more uniform distribution of Eu3+ ions resulting in the increased emission properties were observed in tantalate system.Influence of various lanthanide ion (Lu, Y, Gd, La) substitutions on the Eu3+ photoluminescence properties in Ln3MO7 host structures was also studied. The difference in emission profiles with different Ln ions demonstrated the influence of long range ordering, coordination of cations and ligand polarizability in the emission probabilities, intensity and quantum efficiency of these phosphor materials. Better luminescence of almost equally competing intensities from all the 4f transitions of Eu3+ was noticed for La3TaO7 system. Photoluminescence properties were further improved in La3TaO7 : Eu3+ phosphors by the incorporation of Ba2+ ions in La3+ site. New red phosphor materials Gd2-xGaTaO7 : xEu3+ exhibiting intense red emissions under UV excitation were prepared. Optimum doping level of Eu3+ in these different host lattices were experimentally determined. Some of the prepared samples exhibited higher emission intensities than the standard Y2O3 : Eu3+ red phosphors. In the present studies, Eu3+ acts as a structural probe determining the coordination and symmetry of the atoms in the host lattice. Results from the photoluminescence studies combined with the powder XRD and Raman spectroscopy investigations helped in the determination of the correct crystal structures and phase formation of the prepared compounds. Thus the controversy regarding the space groups of these compounds could be solved to a great extent. The variation in the space groups with different cation substitutions were discussed. There was only limited understanding regarding the various influential parameters of the photoluminescence properties of phosphor materials. From the given studies, the dependence of photoluminescence properties on the crystal structure and ordering of the host lattice, site symmetries, polarizability of the ions, distortions around the activator ion, uniformity in the activator distribution, concentration of the activator ion etc. were explained. Although the presented work does not directly evidence any application, the materials developed in the studies can be used for lighting applications together with other components for LED lighting. All the prepared samples were well excitable under near UV radiation. La3TaO7 : 0.15Eu3+ phosphor with high efficiency and intense orange red emissions can be used as a potential red component for the realization of white light with better color rendering properties. Gd2GaTaO7 : Eu3+, Bi2+ red phosphors give good color purity matching to NTSC standards of red. Some of these compounds exhibited higher emission intensities than the standard Y2O3 : Eu3+ red phosphors. However thermal stability and electrical output using these compounds should be studied further before applications. Based on the studies in the closely related Ln3MO7 structures, some ideas on selecting better host lattice for improved luminescence properties could be drawn. Analyzing the CTB position and the number of emission splits, a general understanding on the doping sites can be obtained. These results could be helpful for phosphor designs in other host systems also, for enhanced emission intensity and efficiency.

Exact algorithms for p-adic fields and epsilon constant conjectures

We develop several algorithms for computations in Galois extensions of p-adic fields. Our algorithms are based on existing algorithms for number fields and are exact in the sense that we do not need to consider approximations to p-adic numbers. As an application we describe an algorithmic approach to prove or disprove various conjectures for local and global epsilon constants.

Optimal Sub-Pixel arrangements and coding for ultra-high resolution three-dimensional OLED displays

Information display technology is a rapidly growing research and development field. Using state-of-the-art technology, optical resolution can be increased dramatically by organic light-emitting diode - since the light emitting layer is very thin, under 100nm. The main question is what pixel size is achievable technologically? The next generation of display will considers three-dimensional image display. In 2D , one is considering vertical and horizontal resolutions. In 3D or holographic images, there is another dimension – depth. The major requirement is the high resolution horizontal dimension in order to sustain the third dimension using special lenticular glass or barrier masks, separate views for each eye. The high-resolution 3D display offers hundreds of more different views of objects or landscape. OLEDs have potential to be a key technology for information displays in the future. The display technology presented in this work promises to bring into use bright colour 3D flat panel displays in a unique way. Unlike the conventional TFT matrix, OLED displays have constant brightness and colour, independent from the viewing angle i.e. the observer's position in front of the screen. A sandwich (just 0.1 micron thick) of organic thin films between two conductors makes an OLE Display device. These special materials are named electroluminescent organic semi-conductors (or organic photoconductors (OPC )). When electrical current is applied, a bright light is emitted (electrophosphorescence) from the formed Organic Light-Emitting Diode. Usually for OLED an ITO layer is used as a transparent electrode. Such types of displays were the first for volume manufacture and only a few products are available in the market at present. The key challenges that OLED technology faces in the application areas are: producing high-quality white light achieving low manufacturing costs increasing efficiency and lifetime at high brightness. Looking towards the future, by combining OLED with specially constructed surface lenses and proper image management software it will be possible to achieve 3D images.

Theoretical study of the physicochemical properties of the light transactinides

A theoretical study of the physicochemical properties of elements 104, 105, and 106 and their compounds in the gas phase and aqueous solutions has been undertaken using relativistic atomic and molecular codes. Trends in properties such as bonding, ionization potentials, electron affinities, energies of electronic transitions, stabilities of oxidation states etc. have been defined within the corresponding chemical groups and within the transactinides. These trends are shown to be determined by increasing relativistic effects within the groups. The behaviour of some gas phase compounds and complexes in solutions is predicted for the gas chromatography and solvent extraction experiments. Redox potentials in aqueous solutions of these elements are estimated.

Time-resolved studies of neutral and ionized Na_n clusters with femtosecond light pulses

The real-time dynamics of Na_n (n=3-21) cluster multiphoton ionization and fragmentation has been studied in beam experiments applying femtosecond pump-probe techniques in combination with ion and electron spectroscopy. Three dimensional wave packet motions in the trimer Na_3 ground state X and excited state B have been observed. We report the first study of cluster properties (energy, bandwidth and lifetime of intermediate resonances Na_n^*) with femtosecond laser pulses. The observation of four absorption resonances for the cluster Na_8 with different energy widths and different decay patterns is more difficult to interpret by surface plasmon like resonances than by molecular structure and dynamics. Timeresolved fragmentation of cluster ions Na_n^+ indicates that direct photo-induced fragmentation processes are more important at short times than the statistical unimolecular decay.

Analytical Study of Light Propagation in Highly Nonlinear Media

The present dissertation is devoted to the construction of exact and approximate analytical solutions of the problem of light propagation in highly nonlinear media. It is demonstrated that for many experimental conditions, the problem can be studied under the geometrical optics approximation with a sufficient accuracy. Based on the renormalization group symmetry analysis, exact analytical solutions of the eikonal equations with a higher order refractive index are constructed. A new analytical approach to the construction of approximate solutions is suggested. Based on it, approximate solutions for various boundary conditions, nonlinear refractive indices and dimensions are constructed. Exact analytical expressions for the nonlinear self-focusing positions are deduced. On the basis of the obtained solutions a general rule for the single filament intensity is derived; it is demonstrated that the scaling law (the functional dependence of the self-focusing position on the peak beam intensity) is defined by a form of the nonlinear refractive index but not the beam shape at the boundary. Comparisons of the obtained solutions with results of experiments and numerical simulations are discussed.

Synthesis and Characterization of Novel Spiro-Starburst-Structures as Blue Light Emitters and Zeolites

Spiro-starburst-structures with symmetric globular structures in forms of first and second generations that readily form stable amorphous glasses have been synthesized and then characterised in this work. During the synthesis of these materials, possibilities of the extension of the chains of the phenyl rings in 2,2’,7 and 7’-positions of the central core of the spirobifluorene as well as the 2’,7 and 7’-positions of the terminal spirobifluorene units of the spiro-starburst-structures have been investigated so that solubilities and morphologies of the compounds are not negatively influenced. Their morphological properties have been explored by recording their decomposition temperature and glass transition temperature. These compounds possessing two perpendicular arrangement of the two molecular halves show high glass transition temperature (Tg), which is one of the most important parameter indicating the stability of the amorphous state of the material for optoelectronic devices like organic light emitting diodes. Within the species of second generation compounds, for example, 4-spiro3 shows the highest Tg (330 °C) and the highest branching degree. When one [4B(SBF)SBF-SBF 84] or two [4SBFSBF-SBF 79] terminal spirobifluorene units are removed, the Tg decreases to 318 °C and 307 °C respectively. Photo absorption and fluorescence spectra and cyclic voltammetry measurements are taken in account to characterize the optoelectronic properties of the compounds. Spiro-starburst-structures emit radiation in the blue region of the visible spectrum. The peak maxima of absorption and emission spectra are observed to be at higher wavelength in the molecules with longer chromophore chains than in the molecules with shorter chromophore chains. Excitation spectra are monitored with their emission peak maxima. The increasing absorbing species in molecule leads to increasing molar extinction coefficient. In the case of 4B(TP)SBF-SBF 53 and 4B(SBF)SBF-SBF 84, the greater values of the molar extinction coefficients (43*104 and 44*104 L mol-1 cm-1 respectively) are the evidences of the presence of four times octiphenyl conjugation rings and eight times terminal fluorene units respectively. The optical properties of solid states of these compounds in the form of thin film indicate that the intermolecular interaction and aggregation of individual molecules in neat amorphous films are effectively hindered by their sterically demanding structures. Accordingly, in solid state, they behave like isolated molecules in highly dilute solution. Cyclic voltammetry measurements of these compounds show electrochemically reversibility and stability. Furthermore, the zeolitic nature (host-guest) of the molecular sieve of the synthesized spiro-starburst-structures has been analysed by thermogravimetric analysis method.

Photoperiod-dependent plasticity of circadian pacemaker center in the brain of the Madeira cockroach Rhyparobia maderae

To various degrees, insects in nature adapt to and live with two fundamental environmental rhythms around them: (1) the daily rhythm of light and dark, and (2) the yearly seasonal rhythm of the changing photoperiod (length of light per day). It is hypothesized that two biological clocks evolved in organisms on earth which allow them to harmonize successfully with the two environmental rhythms: (1) the circadian clock, which orchestrates circadian rhythms in physiology and behavior, and (2) the photoperiodic clock, which allows for physiological adaptations to changes in photoperiod during the course of the year (insect photoperiodism). The circadian rhythm is endogenous and continues in constant conditions, while photoperiodism requires specific light inputs of a minimal duration. Output pathways from both clocks control neurosecretory cells which regulate growth and reproduction. This dissertation focuses on the question whether different photoperiods change the network and physiology of the circadian clock of an originally equatorial cockroach species. It is assumed that photoperiod-dependent plasticity of the cockroach circadian clock allows for adaptations in physiology and behavior without the need for a separate photoperiodic clock circuit. The Madeira cockroach Rhyparobia maderae is a well established circadian clock model system. Lesion and transplantation studies identified the accessory medulla (aMe), a small neuropil with about 250 neurons, as the cockroach circadian pacemaker. Among them, the pigment-dispersing factor immunoreactive (PDF-ir) neurons anterior to the aMe (aPDFMes) play a key role as inputs to and outputs of the circadian clock system. The aim of my doctoral thesis was to examine whether and how different photoperiods modify the circadian clock system. With immunocytochemical studies, three-dimensional (3D) reconstruction, standardization and Ca2+-imaging technique, my studies revealed that raising cockroaches in different photoperiods changed the neuronal network of the circadian clock (Wei and Stengl, 2011). In addition, different photoperiods affected the physiology of single, isolated circadian pacemaker neurons. This thesis provides new evidence for the involvement of the circadian clock in insect photoperiodism. The data suggest that the circadian pacemaker system of the Madeira cockroach has the plasticity and potential to allow for physiological adaptations to different photoperiods. Therefore, it may express also properties of a photoperiodic clock.

Characterization of the molecular clockwork in the cockroach Rhyparobia maderae

Der Wechsel von Tag und Nacht erzeugt einen regelmäßigen Rhythmus von verschiedenen Umweltreizen, allen voran Licht und Temperatur. Fast jedes bis zum heutigen Tage untersuchte Lebewesen besitzt einen endogenen Mechanismus zur Zeitwahrnehmung, und diese "innere Uhr" befähigt Lebewesen dazu, sich vorausschauend an rhythmische Umwelt-Änderungen anzupassen. Circadiane Rhythmen bestehen auch ohne jegliche äußere Reize und basieren auf einem molekularen Rückkopplungs-Mechanismus, der Rhythmen in Genexpression und Proteinkonzentration von etwa 24 Stunden erzeugt. Obwohl sich die grundsätzlichen Mechanismen und Komponenten dieses molekularen Uhrwerks in allen Insekten ähneln, zeigte sich jedoch immer mehr, dass es im Detail doch wesentliche Unterschiede zwischen verschiedenen Insektengruppen gibt. Während das molekulare Uhrwerk der Fruchtfliege Drosophila melanogaster inzwischen sehr gut untersucht ist, fehlen bei den meisten Insektengruppen immernoch eingehende Untersuchungen. Fast nichts ist über die molekulare Basis von circadianen Rhythmen bei der Schabe Rhyparobia maderae bekannt, obwohl diese Art bereits seit Langem als Modellorganismus in der Chronobiologie dient. Um mit der Forschung am molekularen, circadianen System von R. maderae zu beginnen, wurde die Struktur und das Expressionsprofil der core feedback loop Gene per, tim1 und cry2 analysiert. Mittels degenerierten Primern und RACE konnte das vollständige offene Leseraster (OLR) von rmPer und rmCry2, und ein Teil des rmTim1 OLR kloniert werden. Eine phylogenetische Analyse gruppierte rmPER und rmCRY2 gemeinsam mit den Orthologa hemimetaboler Insekten. Viele bei D. melanogaster funktionell charakterisierte Domänen sind bei diesen Proteinen konserviert, was auf eine ähnliche Funktion in der inneren Uhr von R. maderae hinweist. Mittels quantitativer PCR konnte gezeigt werden, dass die mRNA von rmPer, rmTim1 und rmCry2 in verschiedenen Lichtregimen in der gleichen Phasenlage Tageszeit-abhängig schwankt. Die Phasenlage stellte sich bei unterschiedlichen Photoperioden jeweils relativ zum Beginn der Skotophase ein, mit Maxima in der ersten Hälfte der Nacht. Auch im Dauerdunkel zeigen sich Rhythmen in der rmTim1 und rmCry2 Expression. Die Amplitude der rmPer Expressionsrhythmen war jedoch so gering, dass keine signifikanten Unterschiede zwischen den einzelnen Zeitgeberzeiten (ZT) festgestellt werden konnten. Mittels Laufrad-Assays wurde untersucht wie Kurz- und Langtag Lichtregime die Verhaltensrhythmen beeinflussen. Es konnten nur Unterschiede in der Periodenlänge unter freilaufenden Bedingungen festgestellt werden, wenn höhere Lichtintensitäten (1000lx) zur Synchronisation (entrainment) genutzt wurden. Die Periode des freilaufenden Rhythmus war bei Tieren aus dem Kurztag länger. Die photoperiodische Plastizität zeigte sich also auch auf Verhaltensebene, obwohl höhere Lichtintensitäten notwendig waren um einen Effekt zu beobachten. Basierend auf den Sequenzen der zuvor klonierten OLR wurden gegen rmPER, rmTIM1 und rmCRY2 gerichtete Antikörper hergestellt. Die Antikörper gegen rmPER und rmTIM1 erkannten in western blots sehr wahrscheinlich spezifisch das jeweilige Protein. Zeitreihen von Gehirngewebe-Homogenisaten zeigten keinen offensichtlichen circadianen Rhythmus in der Proteinkonzentration, wahrscheinlich auf Grund einer Oszillation mit niedriger Amplitude. In Immunhistochemischen Färbungen konnte nur mit dem gegen rmPER gerichteten Antikörper aus Kaninchen ein Signal beobachtet werden. Beinahe jede Zelle des Zentralnervensystems war rmPER-immunreaktiv im Zellkern. Es konnten keine Unterschiede zwischen den untersuchten ZTs festgestellt werden, ähnlich wie bei den western blot Zeitreihen. In dieser Studie konnten erstmals molekulare Daten der circadianen Uhr von R. maderae erfasst und dargestellt werden. Die Uhrgene per, tim1 und cry2 werden in dieser Schabenart exprimiert und ihre Domänenstruktur sowie das circadiane Expressionsmuster ähneln dem hypothetischen ursprünglichen Insektenuhrwerk, welches der circadianen Uhr von Vertebraten nahesteht. Das molekulare Uhrwerk von R. maderae kann sich an unterschiedliche Photoperioden anpassen, und diese Anpassungen manifestieren sich im Expressionsprofil der untersuchten Uhrgene ebenso wie im Verhalten.

Asymptotic model for shape resonance control of diatomics by intense non-resonant light

We derive a universal model for atom pairs interacting with non-resonant light via the polarizability anisotropy, based on the long range properties of the scattering. The corresponding dynamics can be obtained using a nodal line technique to solve the asymptotic Schrödinger equation. It consists of imposing physical boundary conditions at long range and vanishing the wavefunction at a position separating the inner zone and the asymptotic region. We show that nodal lines which depend on the intensity of the non-resonant light can satisfactorily account for the effect of the polarizability at short range. The approach allows to determine the resonance structure, energy, width, channel mixing and hybridization even for narrow resonances.

Asymptotic model for shape resonance control of diatomics by intense non-resonant light: universality in the single-channel approximation

Non-resonant light interacting with diatomics via the polarizability anisotropy couples different rotational states and may lead to strong hybridization of the motion. The modification of shape resonances and low-energy scattering states due to this interaction can be fully captured by an asymptotic model, based on the long-range properties of the scattering (Crubellier et al 2015 New J. Phys. 17 045020). Remarkably, the properties of the field-dressed shape resonances in this asymptotic multi-channel description are found to be approximately linear in the field intensity up to fairly large intensity. This suggests a perturbative single-channel approach to be sufficient to study the control of such resonances by the non-resonant field. The multi-channel results furthermore indicate the dependence on field intensity to present, at least approximately, universal characteristics. Here we combine the nodal line technique to solve the asymptotic Schrödinger equation with perturbation theory. Comparing our single channel results to those obtained with the full interaction potential, we find nodal lines depending only on the field-free scattering length of the diatom to yield an approximate but universal description of the field-dressed molecule, confirming universal behavior.

Noise Reduction Using Low Weight and Constant Weight Coding Techniques

Signalling off-chip requires significant current. As a result, a chip's power-supply current changes drastically during certain output-bus transitions. These current fluctuations cause a voltage drop between the chip and circuit board due to the parasitic inductance of the power-supply package leads. Digital designers often go to great lengths to reduce this "transmitted" noise. Cray, for instance, carefully balances output signals using a technique called differential signalling to guarantee a chip has constant output current. Transmitted-noise reduction costs Cray a factor of two in output pins and wires. Coding achieves similar results at smaller costs.