Search results for "absorption."
showing 10 items of 2682 documents
Precursor effects of the Rhombohedral-to-Cubic Phase Transition in Indium Selenide
2002
We report on the observation of precursor effects of the rhombohedral-to-cubic phase transition in Indium Selenide (InSe) with several experimental techniques. The pressure at which these precursor defects are first observed depends on the sensitivity of the experimental technique. In transport measurements, which are very sensitive to low defect concentrations, precursor effects are observed 5 to 6 GPa below the phase transition pressure whereas in X-ray diffraction measurements precursor effects are only observed 2 GPa below the phase transition pressure. We report optical absorption measurements, in which the precursor effects are shown by the growth and propagation of dark linear defect…
Dynamic Diglyme-Mediated Self-Assembly of Gold Nanoclusters
2015
We report the assembly of gold nanoclusters by the nonthiolate ligand diglyme into discrete and dynamic assemblies. To understand this surprising phenomenon, the assembly of Au20(SC2H4Ph)15-diglyme into Au20(SC2H4Ph)15-diglyme-Au20(SC2H4Ph)15 is explored in detail. The assembly is examined by high-angle annular dark field scanning transmission electron microscopy, size exclusion chromatography, mass spectrometry, IR spectroscopy, and calorimetry. We establish a dissociation constant for dimer to monomer conversion of 20.4 μM. Theoretical models validated by transient absorption spectroscopy predict a low-spin monomer and a high-spin dimer, with assembly enabled through weak diglyme oxygen-g…
<title>Coumarin fluorescent probes by electro-optical and laser spectrofluorimetry methods</title>
1997
Modified electro-optical absorption and emission methods were used to measure the dipole moments of six coumarin fluorescent probes (CU1, CU4, CU7, CU30, CU120, CU334) in the equilibrated ground, excited Franck-Condon and equilibrated excited states. The measurements were performed in cyclohexane and dioxane at room temperature. The equilibrated ground and excited states dipole measured by electro-optical methods are compared with those derived from other measurements techniques and from semiempirical calculations. Experiments and calculations performed in this work reveal a set of anomalous and interesting properties of CU7 and CU30 in solutions. The spectral dependence of some electro-opt…
Elongated push–pull diphenylpolyenes for nonlinear optics: molecular engineering of quadratic and cubic optical nonlinearities via tuning of intramol…
1999
Abstract Push–pull polyenes are of particular interest for nonlinear optics (NLO) as well as model compounds for long-distance intramolecular charge transfer (ICT). In order to tune the ICT phenomenon and control the linear and nonlinear optical properties, we have synthesized and investigated several series of soluble push–pull diphenylpolyenes of increasing length and having various donor (D) and acceptor (A) end groups. Their linear and NLO properties have been studied by performing electro-optical absorption measurements (EOAM) and third-harmonic generation (THG) experiments in solution. Each push–pull molecule exhibits an intense ICT absorption band in the visible characterized by an i…
Charge transfer states of C2 in Kr clusters
2004
Abstract Ab initio and diatomics-in-ionic-systems (DIIS) calculations are carried out for the C 2 –Kr pair and C 2 –Kr n clusters, respectively. Energetics and transition dipole moments between the ground and excited states are obtained from the calculations. This data is then used to predict the UV charge transfer absorption spectrum of C 2 embedded in Kr n clusters with n = 1, 12, and 224. The results reveal discrete structure in the computed UV spectrum, which is mainly related to the spin–orbit splitting of Kr + .
Ab initio calculations for the far infrared collision induced absorption by N2 gas
2014
We present (far-infrared) Collision Induced Absorption (CIA) spectra calculations for pure gaseous N2 made for the first time, from first-principles. They were carried out using classical molecular dynamics simulations based on ab initio predictions of both the intermolecular potential and the induced-dipole moment. These calculations reproduce satisfactory well the experimental values (intensity and band profile) with agreement within 3% at 149 K. With respect to results obtained with only the long range (asymptotic) dipole moment (DM), including the short range overlap contribution improves the band intensity and profile at 149 K, but it deteriorates them at 296 K. The results show that t…
Use of the red-edge excitation effect for investigation of dielectric interactions in biomembranes
1999
Dipole moments of the fluorescent probes 1-phenylnaphthylamine (1-AN) and 1-anilinonaphthalene-8-sulfonate (1,8-ANS) are measured using electro-optical absorption and emission methods. Dipole moments in the ground and excited states were measured in cyclohexane and dioxane. It is shown that the charge distributions in the 1-AN and 1,8-ANS molecules differ substantially. The spectral dependence of the electro-optical coefficients suggests that the absorption spectrum of 1,8-ANS is due to a superposition of (at least two) electronic transitions. It is found that spectra of 1-AN in erythocyte ghosts are inhomogeneously broadened. The above effect makes it possible to selectively excite probe m…
<title>Electro-optical and fluorescence lifetime studies of aminophthalimide probes in liquids</title>
1995
The modified electro-optical absorption and emission methods are described as well as their use for measurements of electrical dipole moments of five aminophthalimides in ground and excited states. It is found that there exists a principal difference between properties of 3- aminophthalimide (3AP) and 4-amino-N-methylphthalimide (4ANMP) in different solvents. The equilibrated dipole moment of 3AP in its excited state is practically independent on the solvent polarity, in comparison with 4ANMP. The possible mechanism of this effect is discussed.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
Enhanced supercontinuum generation in tapered tellurite suspended core fiber
2015
Abstract We demonstrate 400-THz (0.6–3.3 µm) bandwidth infrared supercontinuum generation in a 10 cm-long tapered tellurite suspended core fiber pumped by nJ-level 200-fs pulses from an optical parametric oscillator. The increased nonlinearity and dispersion engineering extended by the moderate reduction of the fiber core size are exploited for supercontinuum optimization on both frequency edges (i.e., 155-THz overall gain), while keeping efficient power coupling into the untapered fiber input. The remaining limitation of supercontinuum bandwidth is related to the presence of the high absorption beyond 3 µm whereas spectral broadening is expected to fully cover the glass transmission window…
Tunable dual-wavelength thulium-doped fiber laser in the range from 2067 to 2073.5 nm
2017
A tunable dual-wavelength lineal cavity Tm-doped fiber laser is presented. The generation of the laser lines is based on the use of cascaded fiber Bragg gratings and a Hi-Bi fiber optic loop mirror.