Tunable diffraction-limited light at 488 nm by single-pass frequency doubling of a broad area diode laser

A laser system that is based on second-harmonic generation of a broad area laser diode and provides 23.2 mW of diffraction-limited light with narrow bandwidth is described. It is tunable from 487.4 to 489 nm. The broad area laser diode is frequency stabilized in an external cavity that yields 800 mW of diffraction-limited light. This infrared light is converted into the visible by use of a 1 cm periodically poled MgO:LiNbO(3) bulk crystal with a measured single-pass conversion efficiency of up to 3.6%/W x cm.     

Optimierung cycloaliphatischer Epoxidharzsysteme mit Siliconkautschuk

The high crosslink density of epoxy resins with high glass transition temperature, high strength, etc., used in many high-performance applications, causes the undesired brittleness of these materials and, hence, internal stress. For the optimization of their properties, cycloaliphatic epoxy resins were modified with elastomeric silicone. Two different modifying concepts, i. e. dispersion and mixing, were characterized using mechanical testing, dynamic-mechanical analysis and scanning electron microscopic studies as well as measurement of the expansion coefficient and the shrinkage. The modification with silicone, in general, reduces the modulus and improves the fracture toughness of the resins. Due to the two-phase structure of the resins prepared by the dispersion method, the glass transition temperature of the epoxy matrix is practically not depressed, and the tendency to enhance stress is less marked compared to the mixing method.     

Shape-dependent regularization for the retrieval of atmospheric state parameter profiles

We present an adaptive regularization approach to retrieve vertical state parameter profiles from limb-sounding measurements with high accuracy. This is accomplished by introducing a dedicated regularization functional based on a reasonable assumption of the profile characteristics. The approach results in shape-dependent weighting during least-squares computations and relies on a Cholesky decomposition of a preselected L(T)L matrix. Our method is compared with established regularization functionals such as optimal estimation and Tikhonov with respect to errors and achievable height resolution. The results show an improved height resolution of the retrieved profiles together with a reduction of absolute and relative errors obtained by test-bed simulations.     

Laser-induced plasma chemistry of the explosive RDX with various metallic nanoparticles

The feasibility of exploiting plasma chemistry to study the chemical reactions between metallic nanoparticles and molecular explosives such as cyclotrimethylenetrinitramine (RDX) has been demonstrated. This method, based on laser-induced breakdown spectroscopy, involves the production of nanoparticles in a laser-induced plasma and the simultaneous observation of time-resolved atomic and molecular emission characteristic of the species involved in the intermediate chemical reactions of the nanoenergetic material in the plasma. Using this method, it has been confirmed that the presence of aluminum promotes the ejection process of carbon from the intermediate products of RDX. The time evolution of species formation, the effects of laser pulse energy, and the effects of trace metal content on the chemical reactions were also studied.     

Tunable 6.8 W narrow bandwidth emission from a single-stripe continuous-wave broad-area laser diode in a simple external cavity

An antireflection-coated broad-area laser diode with an emitter size of 400 microm x 1 microm and a chip length of 1500 microm is operated in a simple external cavity. For wavelength stabilization and to narrow the bandwidth a diffraction grating in a Littrow configuration is used. At an injection current of 9 A up to 6.8 W of optical output power and a resulting slope efficiency of 0.8 W/A could be achieved. Further, the bandwidth could be narrowed to 100 pm (FWHM), and a tuning range of 40 nm around 976 nm was obtained.     

Standoff detection of chemical and biological threats using laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy (LIBS) is a promising technique for real-time chemical and biological warfare agent detection in the field. We have demonstrated the detection and discrimination of the biological warfare agent surrogates Bacillus subtilis (BG) (2% false negatives, 0% false positives) and ovalbumin (0% false negatives, 1% false positives) at 20 meters using standoff laser-induced breakdown spectroscopy (ST-LIBS) and linear correlation. Unknown interferent samples (not included in the model), samples on different substrates, and mixtures of BG and Arizona road dust have been classified with reasonable success using partial least squares discriminant analysis (PLS-DA). A few of the samples tested such as the soot (not included in the model) and the 25% BG:75% dust mixture resulted in a significant number of false positives or false negatives, respectively. Our preliminary results indicate that while LIBS is able to discriminate biomaterials with similar elemental compositions at standoff distances based on differences in key intensity ratios, further work is needed to reduce the number of false positives/negatives by refining the PLS-DA model to include a sufficient range of material classes and carefully selecting a detection threshold. In addition, we have demonstrated that LIBS can distinguish five different organophosphate nerve agent simulants at 20 meters, despite their similar stoichiometric formulas. Finally, a combined PLS-DA model for chemical, biological, and explosives detection using a single ST-LIBS sensor has been developed in order to demonstrate the potential of standoff LIBS for universal hazardous materials detection.     

Influence of Heat Treatment on the Performance Characteristics of a Plastic Mold Steel

Processing of polymers depends on corrosion‐ and wear resistant tool materials being in direct contact with the feedstock material. Plastic mold steels, a special group of tool steels, are successfully applied here, offering both a good wear and corrosion resistance. The lifetime of tools used for plastic processing not only depends on wear and corrosion resistance but also on the mechanical properties of the tool material for example, its flexural strength. In this work, mechanical tests of a commercial plastic mold steel were performed and related to the heat treatment. A close correlation of the amount of retained austenite and carbides and the mechanical properties was encountered. The paper discusses strategies to optimize the mechanical properties by an adequate heat treatment with regard to the resulting corrosion and wear resistance.     

Isolation and characterization of main albumin fractions of seeds from sunflower (Helianthus annuus L.) and rape (Brassica napus L.)]

The main fractions of the albumins from sunflower and rapeseeds (isolated by means of precipitation with ammonium sulphate or tannin + caffeine and subsequent gel chromatography) are low-molecular, very basic proteins. Their molecular weights range from 10 000 to 16 000, and their isoelectric points (determined by isoelectric focusing and free electrophoresis) are situated at pH greater than 10.0. From the circular dichroism in the wavelength range from 200 to 240 nm it is deduced that the main fraction of the rape albumin is a well-structured protein with 40-46% alpha-helix in aqueous and salt-containing solutions. Denaturation by heating is achieved only at temperatures about 100 degrees C and pH values greater than 9. 20% alpha-helix are left after the action of 8 M urea. This conformational stability is explained by the presence of disulphide linkages in the molecule.     

Selected physico-chemical properties of succinylated legumin from pea (Pisum sativum L.)

Selected physico-chemical properties of pea legumin before and after succinylation have been investigated using isoelectric focusing, PAGE, SDS-PAGE, hydrophobicity measurements, SE-HPLC and RP-HPLC. Exhaustive succinylation shifted the I.P. of legumin from 4.75 to 3.5. The stepwise dissociation of legumin by increasing succinylation has been confirmed both by means of PAGE in a nondenaturing system, and by SE-HPLC. The results of SDS-PAGE provided evidence for the exposure of α-polypeptide chains in the native legumin. High succinylation resulted in a decrease of the surface hydrophobicity (S₀) measured by both fluorescence probes (cis-parinaric acid and anilino-naphtalene sulfonic acid). RP-HPLC gave a response both to conformational changes and the introduced succinyl residues.