Power-scalable system of phase-locked single-mode diode lasers

The direct use of diode lasers for high-power applications in material processing is limited to applications with relatively low beam quality and power density requirements. To achieve high beam quality one must use single-mode diode lasers, however with the drawback of relatively low optical output powers from these components. To realize a high-power system while conserving the high beam quality of the individual emitters requires coherent coupling of the emitters. Such a power-scalable system consisting of 19 slave lasers that are injection locked by one master laser has been built and investigated, with low-power diode lasers used for system demonstration. The optical power of the 19 injection-locked lasers is coupled into polarization-maintaining single-mode fibers and geometrically superimposed by a lens array and a focusing lens. The phase of each emitter is controlled by a simple electronic phase-control loop. The coherence of each slave laser is stabilized by computer control of the laser current and guarantees a stable degree of coherence of the whole system of 0.7. An enhancement factor of 13.2 in peak power density compared with that which was achievable with the incoherent superposition of the diode lasers was observed.     

Optical in-well pumping of a semiconductor disk laser with high optical efficiency

Optical in-well pumping is shown to lead to highly efficient operation of semiconductor disk-lasers using resonant absorption or using external optics. Pump radiation absorption of 70% at 940 nm is demonstrated for a laser emitting around 980 nm. Laser output power was 1.9 W with slope efficiencies up to 35% based on the incident power.     

CHANGES IN THE COMPOSITION AND PROPERTIES OF THE VACUUM RESIDUES AS A RESULT OF VISBREAKING

ABSTRACT

Two vacuum residues of heavy petroleum blends and residues of the products of their visbreaking, on a commercial unit, were investigated by means of column chromatography, cryoscopic analysis, elemental analysis, NMR spectroscopy, etc. An increase in the contents of asphaltenes and saturated, increase in asphaltenes/polar components ratio, and decrease in the aromatics contents during visbreaking were observed for both kinds of feed. The N/C ratio increased, the S/C ratio did not change significantly. Most of the nickel and vanadium were concentrated in the asphaltenes and aromatics. The length of the paraffinic chains of the saturated decreases during visbreaking from about 50 to 30 carbon atoms. The number of carbon atoms per alkyl chain and the number of naphthenic rings in the average molecule of the aromatics decreased, whereas the number of aromatic rings increased. About 2/3 of the total aromatic carbon in the aromatics are non-bridged. The average asphaltenes molecule contains about 36-38 aromatic rings (mostly condensed), 5-7 naphthenic rings and 12-16 alkyl substituents having relatively short (n = 5-6) chains. Two contrary processes, relating asphaltenes, take place during visbreaking: 1) cracking of asphaltenes, which results in a decrease in their content and molecular weight, decrease in the number of the side chains and their length, and increase in asphaltenes aromaticity; 2) asphaltenes formation from the polar components of the feed. The resulting process may be expressed both in a decrease and in an increase in the asphaltenes content. Reactions of condensation of the asphaltenes precursors (resins, etc.) prevail for the light stocks. For heavier stocks, cracking of the asphaltenes plays a more significant role, and the increase in asphaltenes content takes place mainly due to concentrating them in the visbreaking residue as a result of the distillation of the visbroken product.     

Polar nitrogen compounds and their behaviour in the drinking water treatment process

Aliphatic and alicyclic amines as well as ethanolamines are extremely polar compounds, frequently found in the environment, and some of them have high toxicity. To address the contamination of selected German surface waters examined and the importance of bank filtration in Eastern Germany, investigations on the behaviour of polar organic nitrogen compounds during water treatment were carried out. Test conditions were designed appropriately for drinking water treatment conditions, and the tests were carried out using model water as well as bank filtrate. Test filter studies of microbial degradation of selected compounds demonstrated the following order of biodegradability: ethanolamine > dimethylamine > pyrrolidine > ethylenediamine. piperidine > diethylamine > morpholine > piperazine > cyclohexylamine. Flocculation tests using iron salts as well as aluminium salts as coagulants showed very low removal rates for the amines. The best results for the removal of the polar organic nitrogen compounds from the water were obtained using ozonation. Based on the reaction-rate constants, the order of degradation by ozone is: piperazine > morpholine > ethylenediamine > piperidine, cyclohexylamine > dimethylamine > ethanolamine > pyrrolidine > diethylamine. Disinfection by chlorine-containing agents under drinking water treatment conditions did not give effective elimination of the selected polar nitrogen compounds.     

Removal of pharmaceuticals during drinking water treatment

The elimination of selected pharmaceuticals (bezafibrate, clofibric acid, carbamazepine, diclofenac) during drinking water treatment processes was investigated at lab and pilot scale and in real waterworks. No significant removal of pharmaceuticals was observed in batch experiments with sand under natural aerobic and anoxic conditions, thus indicating low sorption properties and high persistence with nonadapted microorganisms. These results were underscored by the presence of carbamazepine in bank-filtrated water with anaerobic conditions in a waterworks area. Flocculation using iron(III) chloride in lab-scale experiments (Jar test) and investigations in waterworks exhibited no significant elimination of the selected target pharmaceuticals. However, ozonation was in some cases very effective in eliminating these polar compounds. In lab-scale experiments, 0.5 mg/L ozone was shown to reduce the concentrations of diclofenac and carbamazepine by more than 90%, while bezafibrate was eliminated by 50% with a 1.5 mg/L ozone dose. Clofibric acid was stable even at 3 mg/L ozone. Under waterworks conditions, similar removal efficiencies were observed. In addition to ozonation, filtration with granular activated carbon (GAC) was very effective in removing pharmaceuticals. Except for clofibric acid, GAC in pilot-scale experiments and waterworks provided a major elimination of the pharmaceuticals under investigation.