Search results for " Optics"

Strategies for structure solution and refinement of small organic molecules from electron diffraction data and limitations of the simulation approach

1999

In recent years, a series of non-linear optically active bis(benzylidene) ketones have been synthesized and investigated by electron crystallography. In most cases, structure refinement was possible by combining electron diffraction analysis and quantum-mechanical calculations with maximum-entropy methods. However, when the torsional angles between the phenyl rings and the C=C double bonds are strongly affected by the crystal field, this method fails because packing-energy calculations are not sufficiently sensitive. This problem can be solved by refining the approximate model with SHELXL, if the data set is sufficiently accurate and the model close to the correct structure. Here it is show…

Structure determination to calculate nonlinear optical coefficients in a class of organic material

1999

A class of molecules with intramolecular two-dimensional charge transfer upon excitation has been synthesized. It is expected that these materials should be prospective candidates for nonlinear optical (NLO) applications such as second harmonic (SHG) generation. In order to optimize the macroscopic NLO properties of the compounds, it is necessary to relate their first hyperpolarizability tensors at a molecular level to those at a crystal bulk level. This requires a complete structure determination and refinement. However, the growth of sufficiently large single crystals, which are needed for structural analysis and refinement by x-ray methods, is a time-consuming and sometimes impossible ta…

Analysis of Σ=3 and Σ=9 Twin Boundaries in Three-Crystal Silicon Ingots

1995

Emission of real phonons due to electron’s self-dressing in a covalent crystal

2011

A slow monoelectronic excitation in a covalent crystal at the temperature T=0 is analyzed. The interaction with zero-point longitudinal acoustic phonons leads to the formation of a dressed electronic state at an energy level lower than that of the initial bare state. This aspect of the dressing process is described here by hypothesizing that the excess of energy is released with the emission of real phonons. Specifically, this paper considers the transition probability from the bare monoelectronic state to a dressed state of the electron accompanied by real phonons and a deformation field. The spectrum of the real phonons emitted during the electronic self-dressing is calculated by applying…

Impurity levels and nonlinear optical properties of doped BaTiO3 from extended cluster LDA calculations

1997

The electronic structures of some transition-metal ions doping the ferroelectric oxide BaTiO3 are calculated through the density functional theory framework (LCAO-LSD ADF method) on extended clusters [XO6Ba8Ti6] embedded in a punctual charge set depicting the crystalline environment. The transition ions X are Fen+(n = 2, 3, 4, 5), Ti3+, Nb4+, and Nb5+. Some related defects like Fe(SINGLE BOND)Vo, where Vo stands for a lacunar oxygen site, are also investigated through a similar process. The positions of impurity levels insides the O2p(SINGLE BOND)Ti3d band gap are obtained from eigenvalues and related optical transition or ionization energies are calculated using excited states. This allows…

Isomer spectroscopy in254No

2006

Isomeric states in No-254 were investigated using a calorimetric method. Two different isomers were found with half-lives of T-1/2 = 266 +/- 2 ms and T-1/2 = 184 +/- 3 mu s, respectively. The domin ...

Quadratic Nonlinear Behaviour of Various Langmuir-Blodgett Molecules

1989

The Langmuir-Blodgett (L-B) technique is well known as a method of building-up ordered arrays of organic molecules, and especially as a means of imposing a noncentrosymmetric structure from molecules that crystallize in a centrosymmetric space group(1–3). L-B films for use in quadratic nonlinear optics can be ordered in a statistically noncentrosymmetric lattice. The method involves the compression of a mono-layer of the organic molecule, spread on top of a water surface, into a two-dimensional solid, followed by the repeated dipping of the substrate to be coated into and out of the subphase. Monolayers may be deposited onto the substrate both on immersion and withdrawal, resulting in a cen…

The influence of sigma and pi acceptors on two-photon absorption and solvatochromism of dipolar and quadrupolar unsaturated organic compounds.

2003

Two-photon absorption cross sections delta and solvatochromic properties were determined for a series of quadrupolar and dipolar compounds by using femtosecond excitation in the spectral range between 710 and 960 nm. The compounds investigated were distyrylbenzenes and polyenes bearing appropriate pi or sigma acceptors. The delta values for the centrosymmetric compounds trans, trans- 1,4-bis[2-(2',5'-dihexyloxy)phenylethenyl]-2,3,5,6-tetrafluorobenzene (6), trans, trans-1,4-bis[2-(4'-dibutylamino)phenylethenyl]- 2,3,5,6-tetrafluorobenzene (2), trans, trans-1,4-bis[2-(4'dimethylamino)phenylbutadienyl]- 2,3,5,6-tetrafluorobenzene (7), trans,-trans-1,4-bis[2-(4'-dimethylamino)phenylethenyl]2,5…

Improved Approach to Liesegang Phenomena

1995

Relationship between microscopic and macroscopic structures of organic thin films for SHG

1993

The experiments described in this paper were undertaken in order to obtain information about the relationship between the structure and non-linear optical properties (second-harmonic generation) of organic thin films. For this purpose, two closely related dyes, diones and tetrones, were compared, both of which are shown to have large hyperpolarisabilities. Their microscopic properties are investigated by conformational analysis and electron diffraction. It could be shown that detailed knowledge about the structure and the adjacent neighbour packing can be obtained from conformational analysis and electron diffraction in order to understand the non-linear optical properties of the two dyes.