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 Title
 NONLINEAR OPTICAL PROPERTIES OF ORGANIC CHROMOPHORES CALCULATED WITHIN TIME DEPENDENT DENSITY FUNCTIONAL THEORY.
 Creator

Tafur, Sergio, Kokoouline, Viatcheslav, University of Central Florida
 Abstract / Description

Time Dependent Density Functional Theory offers a good accuracy/computational cost ratio among different methods used to predict the electronic structure for molecules of practical interest. The Coupled Electronic Oscillator (CEO) formalism was recently shown to accurately predict Nonlinear Optical (NLO) properties of organic chromophores when combined with Time Dependent Density Functional Theory. Unfortunately, CEO does not lend itself easily to interpretation of the structure activity...
Show moreTime Dependent Density Functional Theory offers a good accuracy/computational cost ratio among different methods used to predict the electronic structure for molecules of practical interest. The Coupled Electronic Oscillator (CEO) formalism was recently shown to accurately predict Nonlinear Optical (NLO) properties of organic chromophores when combined with Time Dependent Density Functional Theory. Unfortunately, CEO does not lend itself easily to interpretation of the structure activity relationships of chromophores. On the other hand, the Sum Over States formalism in combination with semiempirical wavefunction methods has been used in the past for the design of simplified essential states models. These models can be applied to optimization of NLO properties of interest for applications. Unfortunately, TDDFT can not be combined directly with SOS because statetostate transition dipoles are not defined in the linear response TD approach. In this work, a second order CEO approach to TDDFT is simplified so that properties of double excited states and statetostate transition dipoles may be expressed through the combination of linear response properties. This approach is termed the a posteriori TammDancoff approximation (ATDA), and validated against highlevel wavefunction theory methods. Sum over States (SOS) and related TwoPhoton Transition Matrix formalism are then used to predict TwoPhoton Absorption (2PA) profiles and anisotropy, as well as Second Harmonic Generation (SHG) properties. Numerical results for several conjugated molecules are in excellent agreement with CEO and finite field calculations, and reproduce experimental measurements well.
Show less  Date Issued
 2007
 Identifier
 CFE0001853, ucf:47372
 Format
 Document (PDF)
 PURL
 http://purl.flvc.org/ucf/fd/CFE0001853
 Title
 COMPUTATIONAL STUDY OF THE NEAR FIELD SPONTANEOUS CREATION OF PHOTONIC STATES COUPLED TO FEW LEVEL SYSTEMS.
 Creator

Tafur, Sergio, Leuenberger, Michael, University of Central Florida
 Abstract / Description

Models of the spontaneous emission and absorption of photons coupled to the electronic states of quantum dots, molecules, NV (single nitrogen vacancy) centers in diamond, that can be modeled as artificial few level atoms, are important to the development of quantum computers and quantum networks. A quantum source modeled after an effective few level system is strongly dependent on the type and coupling strength the allowed transitions. These selection rules are subject to the WignerEckert...
Show moreModels of the spontaneous emission and absorption of photons coupled to the electronic states of quantum dots, molecules, NV (single nitrogen vacancy) centers in diamond, that can be modeled as artificial few level atoms, are important to the development of quantum computers and quantum networks. A quantum source modeled after an effective few level system is strongly dependent on the type and coupling strength the allowed transitions. These selection rules are subject to the WignerEckert theorem which specifies the possible transitions during the spontaneous creation of a photonic state and its subsequent emission. The model presented in this dissertation describes the spatiotemporal evolution of photonic states by means of a Diraclike equation for the photonic wave function within the region of interaction of a quantum source. As part of this aim, we describe the possibility to shift from traditional electrodynamics and quantum electrodynamics, in terms of electric and magnetic fields, to one in terms of a photonic wave function and its operators. The mapping between these will also be presented herein. It is further shown that the results of this model can be experimentally verified. The suggested method of verification relies on the direct comparison of the calculated density matrix or Wigner function, associated with the quantum state of a photon, to ones that are experimentally reconstructed through optical homodyne tomography techniques. In this nonperturbative model we describe the spontaneous creation of photonic state in a nonMarkovian limit which does not implement the WeisskopfWigner approximation. We further show that this limit is important for the description of how a single photonic mode is created from the possibly infinite set of photonic frequencies $\nu_k$ that can be excited in a dielectriccavity from the vacuum state. We use discretized centraldifference approximations to the space and time partial derivatives, similar to finitedifference time domain models, to compute these results. The results presented herein show that near field effects need considered when describing adjacent quantum sources that are separated by distances that are small with respect to the wavelength of their spontaneously created photonic states. Additionally, within the future scope of this model,we seek results in the Purcell and Rabi regimes to describe enhanced spontaneous emission events from these fewlevel systems, as embedded in dielectric cavities. A final goal of this dissertation is to create novel computational and theoretical models that describe single and multiple photon states via single photon creation and annihilation operators.
Show less  Date Issued
 2011
 Identifier
 CFE0003881, ucf:48739
 Format
 Document (PDF)
 PURL
 http://purl.flvc.org/ucf/fd/CFE0003881