Efficient,Reversible Redox‐Switching of Molecular First Hyperpolarizabilities in Ruthenium(II) Complexes Possessing Large Quadratic Optical Nonlinearities

Low‐energy metal‐to‐ligand charge‐transfer (MLCT) excitations are associated with the very large molecular nonlinear optical (NLO) coefficients, β, of the complexes [Ru^II(NH₃)₅(N‐R‐4,4′‐bipyridinium)]³⁺ (R=methyl, phenyl, or 4‐acetylphenyl). Chemical oxidation to the Ru^III forms causes bleaching of the MLCT absorptions and marked attenuation of the NLO responses. Both effects are completely reversed upon re‐reduction, and the extent of the β switching is about 10‐ to 20‐fold.     

Elastic recovery of immiscible blends Part 2: Transient flow histories

Immiscible polymer blends are known to display an unusual elastic recovery after stress release. Recoil after steady-state shearing is well understood and obeys specific scaling relations. Releasing the stress before the steady-state morphology has been reached results in a more complex elastic recovery, including very large final values. This behaviour is investigated systematically. Model blends are used, consisting of nearly inelastic components; hence the measured recoil can be attributed totally to contributions from the interface. The instantaneous structure at the onset of the recoil can vary greatly in transient experiments, ranging from slightly deformed droplets to highly elongated filaments. The effects of this initial structure on the ultimate recoil and time scale of the recovery are studied. The morphological changes during recovery are considered as well. It is demonstrated that they can be computed from the normal stresses during stress relaxation with comparable initial morphologies. This indicates that the same morphological changes occur during stress relaxation and constrained recoil. A scaling relation for the recoil curves has been derived from the Doi-Ohta theory, which is confirmed by the experiments. Received: 9 December 1998 Accepted: 5 April 1999     

Light-induced multi-wavelength lasing in dye-doped chiral nematic liquid crystals due to strong pumping illumination

The influence of the pump laser beam on the lasing spectral characteristics in dye-doped cholesteric liquid crystal is investigated. Under the influence of the pump laser pulses with different repetition rates and energies, non-linear reorientation and light-induced flow reorientation of chiral nematic liquid crystals (CLC) molecules was observed. Independent of the reorientation mechanism, multi-wavelength lasing was achieved due to stepwise uncoiling of the CLC structure. Under the influence of a pump laser beam with low repetition rate, Cano–Grandjean disclination defect lines were induced which remain even after removal of the laser beam.     

Tetraalkynyl calix[4]arenes with advanced NLO properties

Rigid, highly conjugated tetraalkynyl-calix[4]arenes synthesised via Sonogashira coupling give rise to improved second-order hyperpolarizability values as determined by hyper-Rayleigh scattering--a technique that in addition to X-ray crystallography also allows for the conformational analysis of the calixarene structures in solution.     

Quantitative analysis of dilute mixtures of SO<Subscript>2</Subscript> in N<Subscript>2</Subscript> at 7.4 μm by difference frequency spectroscopy

We describe a 7.4-μm source based on difference frequency generation with 6.5 mW of 1278-nm radiation from an extended cavity laser and 66 mW of 1544-nm radiation from another extended cavity laser, amplified in an erbium-doped fibre amplifier. Optimum focusing of the input beams in the 5×5×10-mm³ AgGaSe₂ crystal, and the spatial and temporal characteristics of the output beam, are determined. The source is used for accurate determination of line parameters for selected lines of the ν₃ band of SO₂, centred at 1361 cm^-1. Subsequently, these lines are used for performing quantitative analysis of gas mixtures containing SO₂ at concentration levels down to 4 ppm without relying on any calibration with certified gas mixtures. This demonstrates the potential of infrared spectroscopy as a primary method for low-concentration gas analysis. Received: 16 January 2003 / Revised version: 19 February 2003 / Published online: 9 April 2003 RID="*" ID="*"Corresponding author. Fax: +45-4593/1137, E-mail: jh@dfm.dtu.dk     

The (22(0)1-00(0)0) Band of CO(2) at 6348 cm(-1): Linestrengths, Broadening Parameters, and Pressure Shifts

The (22(0)1-00(0)0) combination band of CO(2) around 6348 cm(-1) is studied with diode-laser spectroscopy, and linestrengths, collision-broadening parameters, and pressure shifts are determined. Linestrengths are modeled with a third-order Herman-Wallis expansion, and discrepancies with values reported in the literature are explained. Copyright 2000 Academic Press.