Dichroism

The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment.

This article provides an up-to-date review on nanocomposites composed of inorganic nanoparticles and the polymer matrix for optical and magnetic applications. Optical or magnetic characteristics can change upon the decrease of particle sizes to very small dimensions, which are, in general, of major interest in the area of nanocomposite materials. The use of inorganic nanoparticles into the polymer matrix can provide high-performance novel materials that find applications in many industrial fields. With this respect, frequently considered features are optical properties such as light absorption (UV and color), and the extent of light scattering or, in the case of metal particles, photoluminescence, dichroism, and so on, and magnetic properties such as superparamagnetism, electromagnetic wave absorption, and electromagnetic interference shielding. A general introduction, definition, and historical development of polymer–inorganic nanocomposites as well as a comprehensive review of synthetic techniques for polymer–inorganic nanocomposites will be given. Future possibilities for the development of nanocomposites for optical and magnetic applications are also introduced. It is expected that the use of new functional inorganic nano-fillers will lead to new polymer–inorganic nanocomposites with unique combinations of material properties. By careful selection of synthetic techniques and understanding/exploiting the unique physics of the polymeric nanocomposites in such materials, novel functional polymer–inorganic nanocomposites can be designed and fabricated for new interesting applications such as optoelectronic and magneto-optic applications.

Novel electro-optic devices using the polarization-, intensity-, and frequency-dependent susceptibility of Stark-active gases have been analyzed and demonstrated, including all-optical limiter/cut-off devices, amplitude modulators, and tunable narrowband filters. The application of the system to other media (e.g., multiple quantum wells) and to the study of coherent optical transients is discussed.

We describe a new iteration of the StereoJet process, which has been simplified by changes in materials and improved by the conversion from linear to circular polarization. A prototype StereoJet process for producing full color stereoscopic images, described several years ago by Scarpetti et al., was developed at the Rowland Institute for Science, now part of Harvard University. The system was based on the inkjet application of inks comprising dichroic dyes to Polaroid Vectograph sheet, a concept explored earlier by Walworth and Chiulli at the Polaroid Research Laboratories. Vectograph sheet comprised two oppositely oriented layers of stretched polyvinyl alcohol (PVA) laminated to opposite surfaces of a cellulose triacetate support sheet. The two PVA layers were oriented at +45 and -45 degrees, respectively, with respect to the running edge of the support sheet. A left-eye and right-eye stereoscopic image pair were printed sequentially on the respective surfaces, and the resulting stereoscopic image viewed with conventional linearly polarized glasses having +45 and -45 degree orientation. StereoJet, Inc. has developed new, simplified technology based on the use of PVA substrate of the type used in sheet polarizer manufacture with orientation parallel to the running edge of the support. Left- and right-eye images are printed at 0 and 90 degrees, then laminated in register. Addition of a thin layer of 1/4-wave retarder to the front surface converts the image pair's respective orientations to right- and left-circular polarization. The full color stereoscopic images are viewed with circularly polarized glasses.

By means of alternating (AC) and direct (DC) photocurrent measurements, the photoelectric dichroism of thin CdS films on glass is demonstrated at 300 K. The samples are formed by pulsed-laser deposition, and defined orientations, i.e. the c-axis perpendicular (CdS⊥) or parallel (CdS∥) to the glass substrate, are achieved by variation of the laser fluence. The AC peaks of the photocurrent spectra of CdS⊥ and CdS∥ are separated by 55 meV. The absorbance spectra prove that the peak shift is caused by absorption dichroism, which is comparable with that of single crystal CdS. The separation of the DC spectra (140 meV) clearly exceeds the value of the absorption dichroism due to long-term trapping of the photocarriers at the surface of the films.

Implementation of the pure-vibrational Raman spectra lidar method for simultaneous measurements of atmospheric water-vapour, aerosol extinction and backscatter coefficients is reported. A Q-switched Nd:YAG laser provides the three elastic wavelengths of 1064, 532 and 355 ...

Abstract : We demonstrate numerically and experimentally a conjugated gammadion chiral metamaterial that uniaxially exhibits huge optical activity and circular dichroism, and gives a negative refractive index. This chiral design provides smaller unit cell size and larger chirality compared with other published planar designs. Experiments are performed at GHz frequencies (around 6 GHz) and are in good agreement with the numerical simulations.

We measured the linear dichroism of several metalloporphyrins embedded in stretched polyvinyl alcohol (PVA) films to estimate the orientation of the absorption transition moments, which in hemoproteins are relevant to the radiationless energy transfer between ...

ABSTRACT Interaction and binding geometries of complexes of Methyl green with poly(dA-dT)2, poly(dA) · poly(dT), and triplex poly(dA) · 2poly(dT) complexes have been studied by linear dichroism. For both of the complexes with double helical DNAs, the z symmetry axis of Methyl green is found to be approximately parallel to the DNA bases while the x symmetry axis lies at 40-44° relative to the local DNA helix axis, in agreement with a groove binding mode. However, in contrast to minor-groove binders (such as DAPI and Hoechst 33258) Methyl green is found to be excluded from binding to the triple helical poly(dA) · 2poly(dT) in which the major groove is filled by the third strand. While most so far studied groove-binding dyes bind in the minor groove of DNA, Methyl green thus appears to be an exception.