Transparent Spectral Region Research Articles

Determination of the absolute configuration of [3(2)](1,4)barrelenophanedicarbonitrile using concerted time-dependent density functional theory calculations of optical rotation and electronic circular dichroism.

The technique of time-dependent density functional theory (TDDFT) has very recently been applied to the calculation of both transparent spectral region optical rotations and electronic circular dichroism (CD). Here, we report the concerted application of the new methodologies to the determination of the absolute configuration (AC) of [3(2)](1,4)barrelenophanedicarbonitrile, 1, the first optically active barrelenophane. 1 is conformationally flexible: the two three-carbon bridges of 1 can each exhibit two conformations, leading to three inequivalent conformations of 1: a, b, and c. Conformational structures and energies are predicted using DFT at the B3LYP/6-31G level. Comparison of the calculated structures to structures obtained via X-ray crystallography of (+)-1 shows that (remarkably) all three conformations a-c are simultaneously present in crystalline (+)-1. The sodium D line specific rotations, [alpha](D), and CD spectra of a-c are calculated using TDDFT at the B3LYP/aug-cc-pVDZ level. Comparison of the conformationally averaged specific rotation and CD spectrum to the experimental data of Matsuda-Sentou and Shinmyozu leads to the AC 9S,12S(+)/9R,12R(-). The same AC is obtained both from [alpha](D) and from the CD, strongly supporting its reliability.

Determination of Absolute Configuration Using Concerted ab Initio DFT Calculations of Electronic Circular Dichroism and Optical Rotation: Bicyclo[3.3.1]nonane Diones

The concerted use of ab initio time-dependent density functional theory (TDDFT) calculations of transparent spectral region optical rotation and of circular dichroism has recently become practicable, permitting the concerted use of transparent spectral region optical rotation and circular dichroism in determining the absolute configurations of chiral molecules. Here, we report concerted TDDFT calculations of the transparent spectral region specific rotations and of the circular dichroism spectra originating in n --> pi C=O group excitations of four bicyclo[3.3.1]nonane diones, 1-4. Comparison to experiment yields absolute configurations for 1-4. For each dione, specific rotations and circular dichroism spectra give identical absolute configurations. Our results are consistent with previous work, with the exception of the Octant Rule-derived absolute configuration of the 2,9-dione.

Correlation between threading dislocation density and the refractive index of AlN grown by molecular-beam epitaxy on Si(111)

We report on the influence of the structural properties on the refractive index of AlN films grown on Si(111) substrates by molecular-beam epitaxy using ammonia. The structural properties are assessed by reflection high-energy electron diffraction, atomic force microscopy, transmission electron microscopy, and x-ray diffraction. Refractive index values are deduced from room-temperature spectroscopic ellipsometry. Optical data analysis is performed using the Kramers-Krönig relation in the transparent spectral region, from 1.6 to 3.2 eV. Evidence is presented showing the influence of strain and dislocation density on the AlN layer refractive index.

Birefringence in two-dimensional bulk photonic crystals applied to the construction of quarter waveplates

We have experimentally measured the birefringence in bulk two-dimensional hexagonal photonic crystals in transparent spectral regions above and below the fundamental band gap. Data is presented for structures with different numbers of layers and two different air-filling fractions. We have used these data to design a photonic crystal quarter waveplate and provide independent experimental demonstrations of its operation.

Determination of absolute configuration using ab initio calculation of optical rotation.

Ab initio Density Functional Theory (DFT) calculations of transparent spectral region, discrete frequency specific rotations were used to assign the absolute configurations (ACs) of: 1, 2H-naphtho[1,8-bc]thiophene 1-oxide; 2, m-F-phenyl glycidic acid methyl ester; 3, o-Br-phenyl glycidic acid methyl ester; 4, p-CH(3)-phenyl glycidic acid methyl ester; 5, 2-(1-hydroxyethyl)-chromen-4-one; and 6, 6-Br-2-(1-hydroxyethyl)-chromen-4-one. The ACs of 5 and 6 were previously determined via X-ray crystallography to be: 5, R(-)/S(+); 6, R(+)/S(-). The ACs obtained using [alpha](D) are the same for both 5 and 6: R(+)/S(-). We conclude that the previously reported AC of 5 is incorrect.

Determination of Absolute Configuration Using Optical Rotation Calculated Using Density Functional Theory

[structure: see text] We report the first determinations of the absolute configurations (ACs) of chiral molecules using discrete frequency, transparent spectral region optical rotations calculated using density functional theory (DFT). The ACs of 2H-naphtho[1,8-bc]thiophene 1-oxide (3), naphtho[1,8-cd]-1,2-dithiole 1-oxide (4), and 9-phenanthryl methyl sulfoxide (5) are determined by comparison of their specific rotations to values calculated via the time-dependent DFT/gauge-invariant atomic orbital (TDDFT/GIAO) methodology using the B3LYP functional and the aug-cc-pVDZ basis set.

Boundary conditions for optical rectification and application to degenerate four-wave mixing in a novel geometry

We derive general boundary conditions for optical rectification of Gaussian beams and discuss the effect on cascaded optical rectification and the linear electro-optic effect as well as terahertz generation. These conditions are applied to degenerate four-wave mixing in a novel geometry in which we experimentally demonstrate, for the first time to our knowledge, that the combination of optical rectification of a single pump beam and the linear electro-optic effect produces a refractive-index grating in the transparent spectral region of the inorganic crystal KNbO3. The intensity of a probe beam diffracted by this grating was determined and corresponds to the theoretically expected result obtained from the known material parameters.

Waveguide writing in chalcogenide glasses by a train of femtosecond laser pulses

Abstract Waveguide writing using a train of femtosecond laser pulses at 850 nm, in the transparent spectral region of bulk As40S60 glasses is reported. Waveguides were written by translating the glass sample along the optical axis of a strongly focussed laser beam. Refractive index variation, linear absorption spectra, and Raman spectra of the exposed region were measured. The chemical mechanism responsible for the index variation has been correlated to a breakage of the glass' As–S bonds and formation of As–As and S–S bonds and increase of the “disorder” of the glass network. The nonlinear optical origin leading to this phenomenon has been shown, and possible mechanisms are discussed.

Dependence of the refractive index of AlxGa1−xN on temperature and composition at elevated temperatures

The refractive index of hexagonal AlxGa1−xN at room temperature and its temperature dependence at elevated temperatures have been determined with high accuracy by spectroscopic ellipsometry. Measurements have been conducted on samples with aluminum molar fractions ranging from 0% to 65% and at temperatures between 290 and 580 K. The refractive index in the transparent spectral region has been determined as a function of photon energy, using the Kramers–Kronig relations with suitable approximations, and applying a multilayer model. An analytical expression for the composition and temperature dependent refractive index in the transparent region, above room temperature, has been obtained. The refractive index has been found to increase with increasing temperature. The shift of the refractive index is strongest for GaN and decreases for AlGaN with increasing aluminum molar fraction. The impact on the properties of GaN based waveguides is illustrated by a slab waveguide calculation.

Theory of the anisotropy of ultrafast nonlinear refraction in zinc-blende semiconductors.

The influence of the higher-conduction-band set ${\mathrm{\ensuremath{\Gamma}}}_{15}^{\mathit{c}}$ on the strength, linear/circular dichroism, and anisotropy of the ultrafast nonlinear refractive index coefficient (${\mathit{n}}_{2}$) is calculated across the transparent spectral region below the fundamental absorption edge for the zinc-blend semiconductors GaAs and InSb. The anisotropy is due entirely to the effects of the higher bands. For GaAs, at the two-photon band edge, and for linearly polarized light, ${\mathit{n}}_{2}$ is predicted to vary by 55% as the crystal orientation is altered relative to the polarization direction. Even larger variations are expected at longer wavelengths. The far lower predicted anisotropy of InSb is consistent with the approximate formula for the strength of the anisotropy coefficient in terms of the ratio of the fundamental to the higher band gap discussed previously for two-photon absorption. The influence of such ${\mathit{n}}_{2}$ anisotropy on propagation in both one-beam and two-beam configurations is discussed. The anisotropy of the optical-switching figure of merit is also evaluated. At frequencies just below the band edge the figure is found to be greatest for radiation linearly polarized parallel to the [001] crystallographic direction; just above the half-band gap and at lower frequencies [111] linear polarization or any circular polarization is favored.

Superluminal (but causal) propagation of wave packets in transparent media with inverted atomic populations.

The propagation of limited-bandwidth signals, such as Gaussian wave packets, tuned to a transparent spectral region far below the resonance of an inverted two-level atomic medium, can be superluminal, i.e., with phase, group, and energy velocities all exceeding the vacuum speed of light c. Causality is not violated, however. Little distortion and gain can accompany this propagation.

Observation of optical Stark effect in InGaAs/InP multiple quantum wells

We report an experimental observation of a blue shift in the n=1 heavy-hole exciton line of In0.53Ga0.47As/InP multiple quantum wells resulting from a picosecond photoexcitation in the transparent spectral region. The temporal response of this shift follows the excitation and it is attributed to the optical Stark effect. The shift was measured to be 0.19 meV for an incident light with a photon energy 20 meV below the exciton peak and with a 10-MW/cm2 intensity.

Refractive Index of ZnS, ZnSe, and ZnTe and Its Wavelength and Temperature Derivatives

Refractive index data of ZnS, ZnSe, and ZnTe were searched, compiled, and analyzed. Recommended values of refractive index for the transparent spectral region were generated in the ranges 0.5–14 μm and 93–1000 K for ZnS, 0.55–18 μm and 93–618 K for ZnSe, and 0.55–30 μm at room temperature for ZnTe. Generation of these values was based on a dispersion equation that best fits selected data sets covering wide temperature and wavelength ranges where the available experimental data permit. Temperature and wavelength derivatives of refractive index were calculated from the first derivatives of the equation with respect to temperature and wavelength, respectively. The results are in concordance with the existing data.

A line parameter list for the ν 2 and ν 4 bands of 12CH 4 and 13CH 4, extended to J′ = 25 and its application to planetary atmospheres

Line parameters (transition frequencies, line strengths, line widths, ground state energies and quantum identifications) for the ν 2 and ν 4 bands of 12CH 4 and 13CH 4 have been calculated for J'⩽25 using the simultaneous coupled fitting procedure of Gray and Robiette. Molecular constants for the ν 2 band of 13CH 4 were estimated from isotopic shifts from 12CH 4 values. Agreement with laboratory spectra, where available, is always well within 1 cm -1 over the entire spectral range covered by the list. The most serious problem in comparison with laboratory data is the omission of lines belonging to “hot” bands in this spectral region. This list is valuable in remote sensing problems for sorting out lines of trace species from weak methane lines and for determining the atmospheric opacity in relatively transparent spectral regions. Applications of the parameter list are demonstrated for remote sounding of the Jovian atmosphere. The list is available on magnetic tape from the authors.

Refractive index of silicon and germanium and its wavelength and temperature derivatives

Refractive index data for silicon and germanium were searched, compiled, and analyzed. Recommended values of refractive index for the transparent spectral region were generated in the ranges 1.2 to 14 μm and 100–740 K for silicon, and 1.9 to 16 μm and 100–550 K for germanium. Generation of these values was based on a dispersion equation which best fits selected data sets covering wide temperature and wavelength ranges. Temperature derivative of refractive index was simply calculated from the first derivative of the equation with respect to temperature. The results are in concordance with the existing dn/dT data.