Giant increase of the second harmonic radiation's absorption during optical poling of oxide glass

Abstract

A giant reversible growth (≥ 10³ times) of the absorption of second harmonic radiation by optical poling of oxide glass was discovered. The observed absorption exerts an influence on the optical poling process and leads to a restriction of the maximum value of the photoinduced second harmonic generation in oxide glass. A theoretical model of the observed phenomenon is given. The growth of absorption is considered as a result of special anharmonic electron-phonon interactions caused by photoinduced electrostricted phonons. Exploration of the total absorption indicates that the effects of photodarkening do not play a key role in the observed phenomena.     

Synthesis of trimethylene carbonate/ϵ‐caprolactone copolymers initiated with zinc alkoxide: influence of copolymer chain microstructure on thermal and mechanical properties

Ethylzinc(II ) ethoxide is a highly active and efficient initiator for the bulk polymerization of 1,3‐trimethylene carbonate and its copolymerization with ? ‐caprolactone. This initiator allows one to obtain (co)polymers with high molar masses in quite a short time. Significant difference in co‐monomer reactivity and relatively low participation of intermolecular transesterification processes lead to the obtained copolymers being characterized by a gradient chain microstructure. In ¹³C NMR spectra, in all regions, we observed the presence of triads which were distinctly represented by four peaks for the carbonyl signal. Mechanical tests showed that copolymers containing 70% and more of ? ‐caprolactone presented a relatively high Young's modulus and a very high maximum elongation factor; therefore these materials are promising in many biomedical applications. Due to the high reaction rate, we also made an attempt at copolymerization using reactive extrusion which gave promising results. © 2017 Society of Chemical Industry     

Application of zirconium (IV) acetylacetonate to the copolymerization of glycolide with ɛ-caprolactone and lactide

Summary A study on the copolymerization of glycolide with lactide and glycolide with ɛ-caprolactone was performed in the presence of zirconium (IV) acetylacetonate at moderate temperatures (100° and 150°C). Zirconium acetylacetonate appeared to be an efficient initiator of copolymerization. The obtained polymers were characterized by high molecular weights. Considerable influence of transesterification on the polymer chain microstructure was found. Received: 13 October 1998/Revised version: 4 January 1999/Accepted: 4 January 1999     

Synthesis of block copolymers of ε-caprolactone and lactide in the presence of lithium t-butoxide

Summary High molecular mass copolymers with microphase separation can be obtained in block copolymerization of -caprolactone with L,L- and D,L-lactide carried out in the presence of lithium t-butoxide. A kind of solvent applied strongly affects the molecular mass and polydispersity index of obtained copolymers.The study has been supported by the research program (Project 4-1743) of the Committee of Scientific Research in Poland.     

Physical properties of iron-sulfur Fe6S6 superclusters important for biological systems

The theoretical analysis of the thermal and magnetic properties of iron-sulfur superclusters has been studied by taking into account Heisenberg interactions and resonance delocalizations (double exchange interactions). The numerical calculations are based on the determination of the lowest energy states for different values of spins (from S = 0.5 to S = 12.5) and Heisenberg exchange integrals. It is shown that the spin magnetic susceptibility of the iron-sulfur superclusters decreases with increasing temperature and increases with increasing the double exchange parameter. In contrast to the susceptibility, the heat capacity decreases with the increasing values of the double exchange parameter. It was theoretically found that spin of ground state for the iron-sulfur supercluster is equal to 0.5. Based on our results, we can state that the Heisenberg model of spin interactions describes the thermodynamic properties of the iron-sulfur superclusters which are the important constituents of proteins and enzymes.     

Predicting the carbonizing period and coking heat of coal charges in horizontal-chamber coke ovens

The carbonizing period and coking heat of coal charges in horizontal-chamber coke ovens have been calculated for different variables influencing the carbonization process by applying two Fourier differential equations. The results from these calculations and from numerous tests in commercial coke ovens were analysed by means of statistical methods. Two regression equations were formulated, enabling the carbonizing period and coking heat to be predicted with sufficient precision.     

Photoinduced nonlinear optical phenomena in Sb2Se3-BaCl2-SnCl2 glasses

Photoinduced nonlinear optical phenomena have been studied in amorphous Sb₂Te₃-CaCl₂-SnCl₂ glasses using photoinduced optical second harmonic generation (SHG). The photoinduced SHG signal was measured for double frequency of a CO₂ laser ( = 5.3 m) using a photoinducing CO laser ( = 5.5 m). We have found that the SHG signal intensity increases with increase of the CO laser photoinducing exposure and achieves its maximum value after 1.5 h. Absolute values of the SHG signals were more than one order in magnitude smaller comparing to a ₂₂₂ tensor component for the ZnSe single crystals. The SHG signal strongly increases if temperature decreases from 39 to 16 K. Femtosecond probe-pump measurements indicate existence of the SHG maximum at pump-probe time delay of about 43 ps. It is suggested that Sb-Se tetrahedra play a key role in the observed photoinduced nonlinear optical effects. Degree of noncentrosymmetry of corresponding bonds depends on time of the CO-laser illumination, temperature and mechanical stresses. Simultaneously, the investigated glasses can serve as promising materials for a femtosecond IR quantum electronics.     

Comparative study of the hydrolytic degradation of glycolide/L‐lactide/ε‐caprolactone terpolymers initiated by zirconium(IV) acetylacetonate or stannous octoate

A series of copolymers have been synthesized by the ring‐opening polymerization of glycolide, L ‐lactide, and ?‐caprolactone with zirconium(IV) acetylacetonate [Zr(Acac)₄] or stannous octoate [Sn(Oct)₂] as the catalyst. The resulting terpolymers have been characterized by analytical techniques such as proton nuclear magnetic resonance, size exclusion chromatography, and differential scanning calorimetry. Data have confirmed that Sn(Oct)₂ leads to less transesterification of polymer chains than Zr(Acac)₄ under similar conditions. The various copolymers have been compression‐molded and allowed to degrade in a pH 7.4 phosphate buffer at 37°C. The results show that the degradation rate depends not only on the copolymer composition but also on the chain microstructure, the Sn(Oct)₂‐initiated copolymers degrading less rapidly than Zr(Acac)₄‐initiated ones with more random chain structures. The caproyl component appears the most resistant to degradation as its content increases in almost all cases. Moreover, caproyl units exhibit a protecting effect on neighboring lactyl or glycolyl units. The glycolyl content exhibits different features: it decreases because of faster degradation of glycolyl units, which are more hydrophilic than caproyl and lactyl ones, remains stable in the case of abundant C? G? C sequences, which are very resistant to degradation, or even increases because of the formation of polyglycolide crystallites. Terpolymers can crystallize during degradation if the block length of one of the components is sufficiently long, even though they are amorphous initially. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008