Processing of transparent materials using visible nanosecond laser pulses

Laser micromachining of transparent materials is an intensively studied research area from the point of view of microoptical element fabrication. One of the most promising indirect processing methods is the laser-induced back-side dry etching (LIBDE). During this method, transparent targets are contacted with solid thin layers, which absorb and transform the pulse energy resulting in etching. The applicability of LIBDE technology for processing of fused silica using a visible nanosecond dye laser (λ=500 nm, FWHM=11 ns) and a 100-nm-thick aluminium absorbing layer was investigated. The applied fluence was varied in the range of 0–3050 mJ/cm²; the illuminated area was 0.1 mm². The threshold fluence of the LIBDE etching of fused silica was found to be approximately 540 mJ/cm². The chemical composition of the surface layers on and around the etched holes was investigated by field-emission scanning electron microscopy and energy-dispersive X-ray spectrometry. It was found that on average 0.4±0.3 at. % aluminium is built into the upper ∼1-μm-thick volume of the illuminated fused silica, while the aluminium content fell below the detection limit in the case of the original surface. Our experiments proved that the LIBDE procedure is suitable for microprocessing of transparent materials using visible nanosecond laser light. PACS 42.62.-b; 61.80.Ba; 81.16.Rf; 81.65.Cf     

Über die Reproduzierbarkeit der turbidimetrischen Bestimmung von Phosphorspuren mit Strychninmolybdostickstoff(V)säure

Microchimica Acta - Mit der turbidimetrischen Strychninnitrat-Methode für Phosphorspurenbestimmung nach der Version von Hegedüs und Dvorszky kann man nur dann ausgezeichnete...     

Measurements of nanoparticle size distribution produced by laser ablation of tungsten and boron-carbide in N2 ambient

Nanoparticles (NPs) were produced by ablating tungsten and boron-carbide (B₄C) target materials in atmospheric pressure nitrogen ambient using ArF excimer laser pulses. The size distributions of the NPs formed during the ablation were monitored—within a 7-133 nm size window—by a condensation particle counter connected to a differential mobility analyzer. The laser repetition rate was varied between 1-50 Hz, and the fluence was systematically changed in the range of 0.5-15 J/cm², for both materials, allowing a comparative study in an extended laser parameter regime. The multishot ablation threshold (Φ_th) of B₄C was determined to be ∼1.9 J/cm² for the laser used (ArF excimer, λ = 193 nm). Similarly to earlier studies, it was shown that the size distributions consist of mainly small nanoparticles (<∼20 nm) attributed to a non-thermal ablation mechanism below Φ_th. An additional broad peak appears (between 20 and 40 nm) above Φ_th as a consequence of the thermally induced macroscopic ablation. Chemical composition of deposited polydisperse nanoparticles was studied by X-ray photoelectron spectroscopy showing nitrogen incorporation into the boron-carbide.     

Minimization of the blank values in the neutron activation analysis of biological samples considering the whole procedure

In our determination of trace element contents of animal tissue by neutron activation analysis in the course of structure-activity relationship studies on platinum containing cancer drugs and wound healing we have tried to minimize the blank values that are caused by different sources of contarnination during surgery, sampling and the activation analysis procedure. The following topics have been investigated: the abrasions from scalpels made of stainless steel, titanium or quartz; the type of surgery; the homogenisation of the samples before irradiation by use of a ball mill; the surface contaminations of the quartz ampoules that pass into the digestion solution of the irradiated samples. The appropriate measures to be taken in order to reduce the blank values are described. The results of analyses performed under these conditions indicate the effectiveness of the given measures, especially shown by the low values obtained for the chromium contents of the analysed muscle samples.     

Determination of antimony in tin by radiochemical neutron activation analysis

New types of correction for chemical yield and counting geometry in conjunction with the comparator method provide significant improvements in reproducibility and sensitivity compared to direct neutron activation analysis.     

Methods, problems and trends of standardization in multielement reactor neutron activation analysis

Summary Features, advantages and drawbacks of the standardization methods (relative, absolute and comparator ones) generally applied in multielement instrumental reactor neutron activation analysis are reviewed. In connection with the applicability of the absolute method, reliability of available nuclear data is discussed in view of recent compilations.

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Methoden, Probleme und Trends der Standardisierung bei der Multielement-Neutronenaktivierungsanalyse mit Reaktorneutronen

Zusammenfassung Ein Überblick wird gegeben über die Merkmale, Vor- und Nachteile der verschiedenen Standardisierungsmethoden (relativ, absolut und Komparator-Methoden), die bei der instrumentellen Multielement-Neutronenaktivierungsanalyse mit Reaktorneutronen allgemein gebräuchlich sind. Im Zusammenhang mit der Anwendbarkeit der Absolut-Methode wird die Zuverlässigkeit von vorhandenen nuklearen Daten in der Sicht neuer Kompilationen diskutiert.

     

Investigations into the characteristics of irradiated zircaloy cladding material in connection with reactor operation and spent fuel reprocessing

To monitor and improve the performance of nuclear fuel assemblies, the uptake of gases (oxygen, nitrogen and hydrogen) is determined in zircaloy cladding materials. Gas chromatography and/or mass spectrometry combined with hot vacuum fusion were applied. Deviations from the initial concentrations (ca. 5 μg g^?1 H₂, 30 μg g^?1 N₂ and 1200 μg g^?1 O₂) in the “as fabricated” condition, are important in estimating cladding corrosion. The material characteristics of zircaloy are altered substantially by the neutron irradiation and the chemical environment in the reactor coolant, thus the irradiated material must also be studied. For reprocessing safety consideration, the ignition and explosion parameters of unirradiated and irradiated zircaloy dusts were examined. Standard methods, tailored to hot-cell operation, were used to evaluate the minimum ignition temperature of a dust layer on a heated surface at constant temperature, the ignition temperature of a dust cloud, the auto-ignition temperature of a cylindrical dust formation as a function of sample volume, and the explosion pressure and pressure rise in a 20-l spherical chamber. Samples of fines (<100 μm diameter) were characterized by measuring their density and particle-size distribution, and by scanning electron microscopy. For samples of irradiated zircaloy, the ignition temperatures were lower and the explosion pressures and pressure rises higher than for unirradiated zircaloy. These findings can be explained by the different particle-size distribution of irradiated material samples. The increased brittleness of the irradiated material produces more small particles (<20 μm) which favour ignition and explosion.     

Three-dimensional focus manipulation by means of a birefringent plate

A method based on double imaging is proposed for three-dimensional focus manipulation. A thin birefringent plate placed behind a focusing lens was applied to generate two foci with a separation smaller than the original DOF. Depth of focus enlargement of 227% was achieved without serious degradation in lateral resolution. Experimental results obtained by using a confocal arrangement were in good agreement with theory. Both theoretical considerations and experimental results showed that in non-paraxial case the ordinary and extraordinary foci could not be excited independently.