Tuning high-power laser diodes with as much as 0.38 W of power and M(2) = 1.2 over a range of 32 nm with 3-GHz bandwidth

Gain-guided diode lasers usually have emission wavelengths determined by the manufacturing process, with typically 0.5-1-nm bandwidth. Furthermore, their beam quality is rather poor. We show that external cavities allow for tunable narrow-bandwidth operation of gain-guided diode lasers. At the same time the beam quality is drastically improved; almost diffraction-limited light of more than 200 mW has been achieved over the whole tuning range from 910 to 942 nm with narrow bandwidth.     

Application of centrifugal vacuum concentrators in residue analysis

Summary Centrifugal vacuum concentrators can be applied in residue analysis successfully: They prevent the samples from bumping and foaming. Even methanol/water- or acetonitrile/water-mixtures as extracts from food or other samples can be concentrated without separation of water prior to the evaporation process. Sulfonamides and other drugs can be concentrated with 100% recovery. Extracts with some light-sensitive substances (nitrofuranes) were evaporated without losses, as well as some hydrolysis-sensitive substances (penicillins) solved in water, whereas tetracyclines decompose in aqueous solution considerably. For more volatile substances (such as organochlorine pesticides or polychlorinated biphenyls) centrifugal vacuum concentrators can be used for preconcentration e.g. of the gelchromatographic eluate. Further, centrifugal vacuum concentrators can automate the evaporation process. In comparison to rotary evaporators, they save time for the laboratory staff when running series of 4 or more samples. It is very important to supply permanently sufficient energy for the evaporation process, especially when concentrating volumes of 10 ml or more. If the only heated part is the wall of the centrifuge, after couple of minutes the samples cool down to very low temperatures, and the evaporation process slows down. A more efficient way to supply evaporation energy is by means of IR radiation. A very modern device offers an electronically controlled IR radiation by means of temperature control on the centrifugal tubes. This in combination with vapour pressure control ensures an optimal control of the most important factors of the evaporation process.     

Liquid crystalline side group polymers with azo-chromophores and fluorinated tails of varying length

A series of side group liquid crystalline polymethacrylates with 4'-(1H,1H-perfluoroalkoxy)-azobenzene mesogenic units was synthesized and characterized by differential scanning calorimetry, polarizing optical microscopy and X-ray diffraction methods depending on the tail length. The phase behaviour is discussed as a function of the length of the tail groups. Very high clearing temperatures up to 290°C were observed for the polymers with long tail groups.     

An yttrium Mξ source for ESCA

A new source for producing YMξ radiation in an ESCA spectrometer is described. The system makes use of continuous evaporation of yttrium on a rotating anode. It is demonstrated that this scheme allows YMξ-excited electron spectra to be recorded without gradual loss of resolution and intensity due to anode oxidation. Electron spectra of Ar, Hg and N₂ excited by YMξ radiation are studied. Relative photoelectric cross-sections of the 5d_{$\text{5}\text{2}$}, 5d_{$\text{5}\text{2}$} and 6s orbitals in Hg and the four valence orbitals in N₂ are measured. The valence electron shake-up spectrum of N₂ is discussed.     

Die zerstörungsfreie Bestimmung der Seltenen Erdelemente nach der Neutronenaktivierung

The technique of INAA for the determination of the rare earth elements with respect to prospecting and production testing of polishing powders on the basis of rare earth element oxides as well as quality testing of ultragrade rare earth compounds is discussed.In order to count -radiation of the radioactive nuclei a Ge-Li-detector as well as a planar Ge-Li-detector have been used. The latter enables the evaluation of the low energetic side of the -spectrum without complicated corrections due to -line interferences. Therefore an efficient working procedure with respect to the determination of the distribution pattern of the rare earth elements is possible.A simple correction program however is necessary with respect to the use of the planar detector type, allowing for effects of self-absorption geometry of the sample as well as distance sample-detector. This program is also given in the paper.

     

Indications about the shape of the universe from the Wilkinson microwave anisotropy probe data

It is shown that the recent observations of NASA's Explorer mission, "Wilkinson Microwave Anisotropy Probe," hint that our Universe may possess a nontrivial topology. As an example we discuss the Picard space which is stretched out into an infinitely long horn but with finite volume.