Nonlinear optical characterization of LaEr(MoO<Subscript>4</Subscript>)<Subscript>3</Subscript> thin films using the <Emphasis Type="BoldItalic">Z</Emphasis> -scan technique

The nonlinear optical properties of thin films of LaEr(MoO₄)₃ were studied using a ∼30 ps Nd:YAG laser at 532 nm with a repetition rate of 250 Hz. Closed aperture Z-scan measurement revealed a negative nonlinearity in the LaEr(MoO₄)₃. The nonlinear refractive index γ=1.38×10^-10 cm²/W and nonlinear absorption coefficient β=16.8×10^-6 cm/W were calculated from the Z-scan data. The fluorescent upconversion spectra were recorded with 980 nm excitation. An optical switching mechanism based on nonlinear absorption is also presented experimentally. PACS 81.15.Fg; 77.84.Bw; 33.50.Dq; 42.70.Mp     

An experimental investigation of inhomogeneities in resonant infrared matrix-assisted pulsed-laser deposited thin polymer films

Thin polymer films are deposited using matrix-assisted pulsed-laser evaporation and subsequently are characterized by scanning electron and atomic force microscopies. An Er : YAG laser (2937 nm, 350 μs) is used as a light source and the effect of the energy density supplied by the laser on the morphology of the deposited films is investigated. It is found that the appearance of undesirable non-uniform morphological features arises from either poor solubility of the guest molecules or insufficient energy density provided by the laser to vaporize the entire ejected volume. In addition, the surface roughness of two guest–host systems is found to depend linearly on the polymer concentration. These results allow us to better understand earlier work in the field and to establish a framework by which MAPLE films may be improved.     

1H n.m.r. spectra of 6-acetoxy-2,4-cyclohexadienones

¹H n.m.r. spectra of 36 derivatives of 6-acetoxy-2,4-cyclohexadienones were analysed. All available evidence indicates that all members of the series have similar conformations which do not depart significantly from planarity. Substituent-induced chemical shifts and interproton coupling constants correlate well with those in the analogously substituted ethylene and benzene derivatives. In particular, it appears that a substituent on the central carbon atom exerts a similar influence on ⁴J(HH) across a ‘W’ path when the three intervening carbon atoms are a part of a benzene ring, an allylic system (i.e. sp³–sp²–sp²), a localized sp²–sp²–sp² system or a saturated (i.e. sp³–sp³–sp³) system.     

Baryon pairs production ine + e − annihilation at\sqrt s = 2.4 GeV

Search for baryon pairs production ine ⁺ e ^? annihilation at \(\sqrt s = 2386 MeV\) is reported. The data relate to a luminosity of 161 nb^?1 collected by the DM2 experiment at DCI, the Orsay colliding ring. First measurements of directe ⁺ e ^? annihilation into \(\Lambda \bar \Lambda \) and ofe ⁺ e ^?→ \(p\bar p\) at this energy are presented. First observation of a goode ⁺ e ^?→ \(n\bar n\) candidate is reported and upper limits are given fore ⁺ e ^?→ \(n\bar n, \Lambda \bar \sum ^0 + c.c.\) and \(\Sigma ^0 \bar \Sigma ^0 \) .     

Resonant infrared pulsed laser deposition of thin biodegradable polymer films

Thin films of the biodegradable polymer poly(DL-lactide-co-glycolide) (PLGA) were deposited using resonant infrared pulsed laser deposition (RIR-PLD). The output of a free-electron laser was focused onto a solid target of the polymer, and the films were deposited using 2.90 (resonant with O-H stretch) and 3.40 (C-H) μm light at macropulse fluences of 7.8 and 6.7 J/cm², respectively. Under these conditions, a 0.5-μm thick film can be grown in less than 5 min. Film structure was determined from infrared absorbance measurements and gel permeation chromatography (GPC). While the infrared absorbance spectrum of the films is nearly identical with that of the native polymer, the average molecular weight of the films is a little less than half that of the starting material. Potential strategies for defeating this mass change are discussed. Received: 22 August 2001 / Accepted: 23 August 2001 / Published online: 17 October 2001     

A study of the partitioning and sorptive behaviour of butyltins in the aquatic environment

This study was designed to investigate the partitioning and sorptive behaviour of tributyltin(TBT), and its degradation products dibutylitin (DBT) and monobutyltin (MBT), in the aquatic environment. Factorial experiments were undertaken to determine the importance of pH and particulate matter concentration in the sorption of butyltin compounds to solid phases. Results indicate that in freshwaters MBT, and to a lesser extent TBT, will be partitioned towards the particulate phase, whereas DBT exhibits a 50:50 partitioning between particulate and solution phases. In estuarine waters, whilst MBT will almost exclusively sorb on to particulates, TBT will be predominantly in the solid-phase fractions but 10–30% may remain in solution. DBT, in contrast, is solubilized in estuarine waters. A more detailed investigation of TBT sorption and particulate matter concentration was undertaken using adsorption isotherms on different sediment types. The results from batch isotherm tests plotted according to the Freundlich adsorption model revealed that TBT adsorption varied with sediment type, increasing in the order sandy-silt < silty-sand < silty-clay. TBT sorption was found to be reversible, indicating that contaminated sediments may release TBT to overlying waters following sediment distrubance. Interstitial water partitioning studies indicate that TBT predominates in the particulate phase with partition coefficients for TBT higher than for DBT and MBT. The TBT partition coefficient in interstitial waters appears to be related to total organic carbon loadings.     

Observation of persistent photoconductivity in conducting polyaniline thin films

Conducting polyaniline thin films have been deposited by a laser-based vaporization technique. The films have been characterized by infrared spectroscopy, UV-Vis spectroscopy, four-point conductivity measurements, thermogravimetric analysis, and fluorescence measurements. In addition, the films have been characterized with respect to their photoconductive response to 532-nm laser light. It is found that the films exhibit persistent photoconductivity and it is proposed that defect base sequences may be responsible for the charge localization that results in such a photoconductive response. PACS 78.66.Qn; 81.15.Fg; 72.80.Le     

Improved J-compensated sequences based on short composite pulses

Efficient J-compensated sequences that are shorter in duration and use less RF pulses have been created from short but very efficient composite 90 degrees RF pulses. The improved J-compensation transforms in-phase into antiphase magnetization and can be incorporated in any pulse sequence that involves evolution of heteronuclear J-couplings. The compensated sequences were tested and incorporated into an HMBC sequence. J-compensated experiments referred to as HMBC-J45 + 90A and HMBC-J45 + 90B, were found to be effective over a wide range of J values.