Sum frequency generation of continuously tunable blue pulses from a two-branch femtosecond fiber source

We report on the generation of femtosecond blue pulses from a two-branch mode-locked erbium-doped fiber source. This is achieved by sum-frequency mixing in β-barium borate between the frequency doubled laser radiation at 770 nm and a tunable near-infrared component generated inside a highly nonlinear fiber. Small angle tuning of the nonlinear crystal leads to a continuously variable output wavelength in the visible band between 460 nm and 500 nm. Average power levels exceeding 1.5 mW were collected throughout the entire tuning range of our device, which delivered sub-300-fs pulses at a repetition rate of 98 MHz. These values indicate that the input near-infrared radiation is up-converted with a photon efficiency of 20%.     

The active centres' nature in anionic polymerization of polar monomers

In the anionic polymerization of polar monomers the nature of active centres is considerably influenced by the reaction conditions. In a survey, the present state of knowledge is represented and discussed for the polymerization of acrylonitrile. Analogous problems of methyl methacrylate and vinylpyridine polymerization are included in the considerations.     

Laser excited luminescence spectra of zirconia

Luminescence spectra of ivory zirconia (Zr0₂) excited by an argon-ion laser (19,436–21,839 cm^?1) reveal a complex pattern consisting of both sharp and diffuse peaks in the 16,000–19,000 cm^?1 region. The intensity behavior of these features depends markedly on the excitation frequency. The sharp luminescence peaks of the 18,140–18,600 cm^?1 region are attributed to phonon-mediated de-excitation of excited states of the impuriity-doped ZrO₂ lattice. The more diffuse luminescence bands of the 17,700–18,000cm^?1 region may be associated with the electron traps observed in glow experiments and/or with higher-order phonon processes.     

Connecting the Dots: Mott for Emulsions,Collapse Models,Colored Noise,Frame Dependence of Measurements,Evasion of the “Free Will Theorem”

We review the argument that latent image formation is a measurement in which the state vector collapses, requiring an enhanced noise parameter in objective reduction models. Tentative observation of a residual noise at this level, plus several experimental bounds, imply that the noise must be colored (i.e., non-white), and hence frame dependent and non-relativistic. Thus a relativistic objective reduction model, even if achievable in principle, would be incompatible with experiment; the best one can do is the non-relativistic CSL model. This negative conclusion has a positive aspect, in that the non-relativistic CSL reduction model evades the argument leading to the Conway–Kochen “Free Will Theorem”.     

Phytotoxicity assessment of diclofenac and its phototransformation products

The occurrence of pharmaceuticals in the environment is an emerging issue. Several studies observed that the non-steroidal anti-inflammatory drug diclofenac is ubiquitously present in most of the surveyed surface waters, worldwide. Phototransformation of diclofenac was reported from laboratory assays as well as in natural water systems, raising the question of possible adverse effects of the phototransformation products of diclofenac to aquatic organisms. In this study the phytotoxicity of diclofenac exposed to natural sunlight was evaluated using synchronized cultures of the unicellular chlorophyte Scenedesmus vacuolatus. Diclofenac dissolved in ultra-pure water at 50 mg L⁻¹ was exposed to natural midsummer sunlight for a maximum of 145 h. Twice a day subsamples were taken for chromatography and parallel phytotoxicity assessment. Inhibition of algal reproduction of the initial diclofenac solution was in the mg L⁻¹ range indicating no specific toxicity of diclofenac towards S. vacuolatus. Fast degradation of diclofenac was observed with half lives between 3.3 and 6.4 h during the first and the third day of exposure, respectively. Phytotoxicity increased after 3.5 h of exposure of diclofenac to sunlight and showed a maximum of sixfold enhanced toxicity after 53 h of exposure to sunlight. Several phototransformation products were found during the experiment. The time courses of the relative concentration of three transformation products significantly correlated with enhanced phytotoxicity during the experiment. This indicates a high toxicity potential of phototransformation products of diclofenac at concentration levels that may come close to environmental concentrations of residual diclofenac after degradation. We conclude that toxicity assessment of phototransformation products should be included in the risk assessment of pharmaceuticals in the environment.