A simple corona phototriggered discharge has been operated in SF6/C2H6/Ne mixture at typical pressures 90-110 Torr, deposited energies up to 180 J/1 and has resulted in the production of high energy HF laser pulse aroung 2.8 j.m. The maximum laser energy was 3.8 J per pulse which corresponds to a specific energy of 7 J/liter and to an efficiency of 4 % based upon the energy stored on the sustaining capacitor. Results of discharge modeling have shown that F atoms were mainly produced by electron excitation of SF6 dissociative electronic states.

From a quantitative inventory of sulphur forms and sulphur budget, the relation between the distribution of the various sulphur forms and the sulphate fluxes in three soil profiles has been addressed. These profiles are located in two forested watersheds at Mont Loz6re. One has been sampled in a beech forest and the other two in a spruce forest and in a harvested plot of this spruce forest, respectively. The mean annual input-output budgets showed a sulphur immobilization in the soil cover of the three plots. In the preserved spruce forest plot, because of larger dry depositions, the sulphur immobilization is much greater than in other plots and occurs essentially in the B horizons. In the other two profiles, the dominant immobilization occurs in the parent material.The total sulphur content is very high in the forest floor reaching 2065 txg S g-1 in the litter of one of the soils under spruce. In the organo-mineral horizons of soils under spruce, the total sulphur content decreases with depth and ranges from 310 to 520/xg S g-I in the A horizons to 100-200/xg S g ~ in the parent material. In the profile under beech, the total sulphur content is lower except in the parent material. In all cases, the organic sulphur is the major part of sulphur often representing more than 90% of total sulphur. In organo-mineral soil horizons of the spruce forest, the part of the sulphateesters is more important than in the soil of the beech forest, probably related to the different nature of the microbial activity in the spruce forest. In contrast, the humification processes are more efficient in the soil under beech, which can be due to the greater input of organic sulphur by litterfall. It appears that the dominant organic sulphur form varies as a function of microbial ecology and sulphate flux. The maximum of the inorganic sulphate is located at the base of the B horizons in the soil of the spruce forest and in the parent material of the soil under beech. In these horizons, the high content of inorganic sulphate can be related to the higher amounts of amorphous Fe and AI phases.

Photoswitching of a homogeneous 1-1 discharge has been tested on a specially designed excimer laser by using either an x-ray beam or a KrF laser beam as a photoionization source. With x rays, a L4-1, 4 X4-cm 2 , XeCllaser beam has been obtained with 1.7% efficiency and an impedance-matched 50-ns pulse-forming line directly connected to the electrodes. Since the output energy seems to rise monotonically as a function of electron-ion pair initial density, even better performances should be attainable with a more intense photoionization source. 754

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