Optical Limiting Characteristics of Dendrons and Dendrimers Incorporating Dithienylpolyene Moieties

1999 ◽  
Vol 597 ◽  
Author(s):  
B. Ozer ◽  
B.-S. Kang ◽  
C. W. Spangler
Keyword(s):  
Excited State ◽  
Cross Section ◽  
Cross Sections ◽  
Excitation Cross Section ◽  
Optical Limiting ◽  
Intersystem Crossing ◽  
Radical Ions ◽  
Saturable Absorbers ◽  
The Past ◽  
Charge States

AbstractOver the past decade there has been considerable progress in the design of new chromophores for potential optical limiting applications. Most of the focus has been centered on molecules that are capable of efficient excited state absorptions whose cross-sections are larger than the original π–π* excitation cross-section, usually referred to as reverse saturable absorbers (RSAs). The vast majority of chromophores having RSA characteristics depend on efficient intersystem crossing from the excited state singlet (S1) to a highly absorbing and relatively long-lived triplet state (T1). However, much less attention has been paid to alternative excited state absorptions, particularly from charge states such as polaronic radical-ions and bipolaronic diions. In this presentation, we propose that monodisperse dendrimers based on dendron coupling to core molecules such as bisphenol A are potential optical limiting materials based on photo-generation of such charge states in the dendron-attached chromophores, such as dithienylpolyenes. The design and syntheses of these dendrons and dendrimers are presented, and the absorption characteristics of the most likely charge states discussed from an optical limiting perspective.

scholarly journals A Study of the Vibrational Excitation of H2 by Measurements of the Drift Velocity of Electrons in H2−Ne Mixtures

1988 ◽  
Vol 41 (4) ◽  
pp. 573 ◽  
Author(s):  
JP England ◽  
MT Elford ◽  
RW Crompton
Keyword(s):  
Cross Section ◽  
Drift Velocity ◽  
Cross Sections ◽  
Excitation Cross Section ◽  
Vibrational Excitation ◽  
Pure Hydrogen ◽  
Velocity Data ◽  
Highly Sensitive ◽  
Hydrogen Mixtures ◽  
Made In

Measurements of electron drift velocities have been made in 1�160% and 2�892% hydrogen-neon mixtures at 294 K and values of EI N from 0�12 to 1�7 Td. The measurements are highly sensitive to the region of the threshold of the v = 0 → 1 vibrational excitation cross section for hydrogen and have enabled more definitive tests of proposed cross sections to be made than was possible using drift velocity data for H2−He and H2−Ar mixtures. The theoretical v = 0 → 1 vibrational excitation cross section of Morrison et al. (1987) is shown to be incompatible with the present measurements. A new set of hydrogen cross sections has been derived from the available electron swarm measurements in pure hydrogen and hydrogen mixtures.

Erbium Doped Tellurite Glasses

1991 ◽  
Vol 244 ◽  
Author(s):  
Jau-Sheng Wang ◽  
Elias Snitzer ◽  
George H. Sigel
Keyword(s):  
Excited State ◽  
Cross Section ◽  
Cross Sections ◽  
Ground State ◽  
Optical Transition ◽  
Emission Cross Section ◽  
Excited State Absorption ◽  
Tellurite Glasses ◽  
Ground State Absorption ◽  
Erbium Doped

ABSTRACTThe results to be presented focus on the optimization of tellurite glass compositions which are suitable both for doping with erbium oxide as well as subsequent for fiber drawing. The laser related properties, such as fluorescence spectrum, lifetime, and optical transition cross sections will be presented. Judd-Ofelt parameters for erbium in the glasses have been exploited to predict fluorescence lifetime, excited state absorption(ESA), ground state absorption(GSA) and ground state fluorescence(GSF). For comparison, the absorption cross section, emission cross section, excited state absorption(ESA)/ground state absorption(GSA)(0.8μm pumping) and fluorescence terminating in the ground state(GSF)/excited state absorption(ESA) ratios are calculated for both Al2O3-SiO2 and tellurite glasses.

Solvent Effects on C60 Excited State Cross Sections

1994 ◽  
Vol 374 ◽  
Author(s):  
Daniel G. McLean ◽  
Donna M. Brandelik ◽  
Mark C. Brant ◽  
Richard L. Sutherland ◽  
Lynn Frock
Keyword(s):  
Excited State ◽  
Cross Section ◽  
Cross Sections ◽  
Solvent Effects ◽  
Nonlinear Absorption ◽  
Equation System ◽  
Survey Study ◽  
Absorption Properties ◽  
Absorption Measurements ◽  
Initial Transmission

AbstractA survey study of solvent effects on the linear and nonlinear absorption properties of C60 has been done. The nonlinear absorption measurements are done at 694 nm with a Q-switched Nd:YAG pumped dye laser. In conjunction with this study a three level rate equation system has been solved analytically and the model results used to extract effective excited state cross sections. A difference and a ratio are calculated from the effective excited state cross section and the ground state cross section. The analysis demonstrates that it is this difference and the initial transmission which determine the critical fluence for the onset of nonlinear absorption. The saturation behavior is determined by the ratio of the cross sections and the initial transmission. Based on these findings C60 is shown to have some of the highest reported nonlinear absorption properties at 694 nm. The effective excited state cross sections at 694 nm are reported for the solutions and correlations to the solvent types demonstrated.

Photoneutron cross sections in 7Li

1977 ◽  
Vol 55 (5) ◽  
pp. 428-433 ◽  
Author(s):  
H. Ferdinande ◽  
N. K. Sherman ◽  
K. H. Lokan ◽  
C. K. Ross
Keyword(s):  
Fine Structure ◽  
Excited State ◽  
Cross Section ◽  
Cross Sections ◽  
Ground State ◽  
Reasonable Agreement ◽  
Branching Ratio ◽  
Energy Spectra ◽  
Average Value ◽  
First Excited State

Photoneutron energy spectra from 7Li have been measured by time-of-flight methods, for bremsstrahlung end-point energies increasing in 2 MeV steps from 13 to 25 MeV. The ground-state and approximate first-excited-state differential cross sections at 90° have been obtained from 8.5 to 23 MeV. No pronounced fine structure has been observed. The measured branching ratio to the first excited state falls from an average value of 0.70 between 10.3 and 14.5 MeV to an average of 0.29 between 14.5 and 18 MeV, and rises again to an average of 0.38 between 18 and 23 MeV. This behaviour can be explained by a crude theoretical model in which 1p → 2s and 1p → 1d single particle transitions dominate below 18 MeV. The calculation predicts a branching ratio of 0.50 near threshold, falling to 0.23 at higher energies, in reasonable agreement with the experiment. The integrated value of the ground-state cross section up to 23 MeV is about (38.7 ± 3.9) MeV mb, while that for the first excited state is about (17.2 ± 3.4) MeV mb. Together they account for 39% of the exchange-augmented dipole sum of 7Li.

PICOSECOND REVERSE SATURABLE ABSORPTION AND OPTICAL LIMITING IN FULLERENES AND THEIR METAL DERIVATIVES

2000 ◽  
Vol 09 (04) ◽  
pp. 505-521 ◽  
Author(s):  
J. CALLAGHAN ◽  
W. J. BLAU ◽  
F. Z. HENARI
Keyword(s):  
Excited State ◽  
Cross Sections ◽  
Ground State ◽  
Population Level ◽  
Optical Limiting ◽  
Saturable Absorption ◽  
Reverse Saturable Absorption ◽  
Picosecond Pulses ◽  
Metal Derivatives ◽  
532 Nm

Investigations of the reverse saturable absorption behaviour of Fullerenes C 60 and C 70 and some of their Pt and Pd metal derivatives have been carried out with picosecond pulses at 532 nm. From intensity dependent transmission measurements, coupled with a population level kinetic analysis, excited state cross sections were determined for the materials. These show that C 60 possesses the largest excited state to ground state cross-section ratio and that, of the materials studied, it offers the best optical limiting ability around 532 nm. C 70, due to its large ground state absorption, has been shown not to be an efficient limiter. The metal derivatives perform better than C 70 but less efficiently than C 60.

Measurement of Excitation Cross-Sections for Electron Impact at low Densities of Target Atoms

1973 ◽  
Vol 28 (11) ◽  
pp. 1871-1872 ◽  
Author(s):  
F. Karstensen ◽  
J. Pohl
Keyword(s):  
Electron Impact ◽  
Cross Section ◽  
Cross Sections ◽  
Atomic Beam ◽  
Excitation Cross Section ◽  
Particle Density ◽  
Measured Cross Section ◽  
Beam Experiment ◽  
Excitation Cross Sections

In a crossed-beam experiment Na atoms are excited by electron impact with an energy of 11 eV. Determination of the excitation cross-section for the D-lines shows an increase of the measured cross-section with decreasing particle density in the atomic beam below 1012 cm-3.

scholarly journals Positron?Lithium Inelastic Scattering with Polarisation Potentials

1991 ◽  
Vol 44 (6) ◽  
pp. 677 ◽  
Author(s):  
M EI-Shabshiry ◽  
SY EI Bakry ◽  
AH Moussa ◽  
MA Abdel-Raouf
Keyword(s):  
Inelastic Scattering ◽  
Cross Section ◽  
Cross Sections ◽  
Excitation Cross Section ◽  
Positronium Formation ◽  
Elastic Channel ◽  
Formation Cross Section ◽  
Positron Energy ◽  
Maximum Value

Positron-lithium inelastic scattering is studied at positron energies ranging from 0�005 to 20 eV using the coupled static model. Two channels are open namely the elastic and positronium formation. The polarisation potentials of the Li atom in the first channel and that of the positronium atom in the second channel are taken into consideration in calculating the corresponding cross sections. The partial cross sections in each channel are calculated for eight values of the total angular momentum (0 ~.e ~ 7). In the elastic channel the total cross section Ull has its maximum value at the lowest energy, and decreases with an increase in positron energy Ki. The total positronium formation cross section has a small dip at 0�1 eV, and maximum value at Ki = 1 �4 eV, and then decreases smoothly with e+ energy. We compare our results with those of Ward et al. (1989) where positronium formation is ignored. The agreement in elastic cross sections improves with e+ energy, while the total collisional cross sections have the closest agreement at 1�0 eV. From this comparison, we find that positronium formation is important in the very low energy region, and the role of the excitation cross section increases steadily with e+ energy.

Photoneutron Reactions in 18O

1975 ◽  
Vol 53 (8) ◽  
pp. 786-794 ◽  
Author(s):  
J. D. Allan ◽  
J. W. Jury ◽  
R. G. Johnson ◽  
K. G. McNeill ◽  
J. G. Woodworth ◽  
...  
Keyword(s):  
Excited State ◽  
Cross Section ◽  
Cross Sections ◽  
Differential Cross ◽  
Ground State ◽  
Energy Spectra ◽  
Continuum State ◽  
Average Value ◽  
First Excited State ◽  
Time Of Flight Spectroscopy

Photoneutron energy spectra from 18O have been measured by time-of-flight spectroscopy at bremsstrahlung endpoint energies from 11 to 18 MeV in 1 MeV steps to obtain the (γ, n0) and (γ, n1) differential cross sections. The ground state photoneutron cross section contains at least 8 major resonances in the region from 10 to 17 MeV and has an average value of 100 μb/sr. The cross section to the first excited state of 17O contains only two major resonances, at 11.4 and 14.4 MeV, and the average cross section in the region from 11 to 16 MeV is about 40 μb/sr. Of particular interest is a resonance at 14.4 MeV which appears to reflect a simple excitation of one of the valence neutrons to the 2p3/2 state. Analysis of the (γ, n0) and (γ, n1) cross sections for this continuum state leads to estimates of the configuration amplitudes of the 2s1/2 and 1d5/2 components of this state to be 0.62 ± 0.06 and 0.78 ± 0.08 respectively and the ratio of the (2s1/2)2 to (1d5/2)2 amplitudes in the ground state of 18O to be 0.39 ± 0.02.

scholarly journals Fold–thrust structures – where have all the buckles gone?

2019 ◽  
Vol 487 (1) ◽  
pp. 21-44 ◽  
Author(s):  
Robert W. H. Butler ◽  
Clare E. Bond ◽  
Mark A. Cooper ◽  
Hannah Watkins
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Narrow Range ◽  
Structural Evolution ◽  
Fault Propagation ◽  
The Past ◽  
Thrust Belts ◽  
Fault Bend ◽  
Shear Failures ◽  
Orogenic Belts

AbstractThe margins to evolving orogenic belts experience near layer-parallel contraction that can evolve into fold–thrust belts. Developing cross-section-scale understanding of these systems necessitates structural interpretation. However, over the past several decades a false distinction has arisen between some forms of so-called fault-related folding and buckle folding. We investigate the origins of this confusion and seek to develop unified approaches for interpreting fold–thrust belts that incorporate deformation arising both from the amplification of buckling instabilities and from localized shear failures (thrust faults). Discussions are illustrated using short case studies from the Bolivian Subandean chain (Incahuasi anticline), the Canadian Cordillera (Livingstone anticlinorium) and Subalpine chains of France and Switzerland. Only fault–bend folding is purely fault-related and other forms, such as fault-propagation and detachment folds, all involve components of buckling. Better integration of understanding of buckling processes, the geometries and structural evolutions that they generate may help to understand how deformation is distributed within fold–thrust belts. It may also reduce the current biases engendered by adopting a narrow range of idealized geometries when constructing cross-sections and evaluating structural evolution in these systems.

Theoretical Calculation of Optical Collisional Cross Sections and α-Parameter Values for Transitions of Interest in Atomic Absorption Spectrometry

1977 ◽  
Vol 31 (5) ◽  
pp. 424-434 ◽  
Author(s):  
R. J. Lovett ◽  
M. L. Parsons
Keyword(s):  
Excited State ◽  
Hyperfine Structure ◽  
Cross Section ◽  
Cross Sections ◽  
Absorption Spectrometry ◽  
Full Width ◽  
Half Maximum ◽  
Line Broadening ◽  
Actual Shape ◽  
Parameter Values

A method has been developed for calculating optical collisional cross sections and subsequent a-parameter values for spectral transitions of interest to analytical atomic spectroscopists. A combination of classical and semiclassical line broadening theory is used. The calculated values compare well (±20% or less) with values determined experimentally for elements without extensive hyperfine structure. If hyperfine structure is significant, the calculated a-parameter can be used to calculate the full width at half maximum of the spectral transition, but not the actual shape. The cross section values are found to correlate well with the proximity of the energy of the excited state of the atom to the ionization energy and to the orbitals involved in the electronic transition (e.g., s-p). A method of converting a values to different flame conditions has also been developed. Cross sections and a-parameter values for a total of 114 transitions from 52 elements have been calculated for the air-acetylene flame.

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