Mixtures of halogen-containing molecules and rare gases have been excited by a short pulse of high energy electrons. The D′→A′ transitions occurring between an ionically bound upper level and a weakly bound covalent lower level in the diatomic halogens F2, Cl2, and interhalogen compounds ClF, ICl, IF, IBr, BrCl, and BrF formed under these conditions have been studied systematically. Emission wavelengths calculated from a simple model are in good agreement with the experimental data. The processes responsible for the population of the upper level have also been studied. The exchange reaction of an electronically excited atom with a halogen donor molecule appears to be the key step in the kinetic excitation sequence. A rate equation model satisfactorily describes the time development of the observed halogen fluorescence. Based on these results, successful laser experiments have been conducted on several of the interhalogen systems.
A krypton-fluorine excimer laser at a 248-nm wavelength was used to irradiate normal and severely atherosclerotic segments of human postnortem femoral arteries. Single pulses and multiple pulses required for penetration or perforation of the arterial wall were applied with 16 nsec pulse width and 5 J/cm2/pulse energy fluence. The total fluorescence of irradiated and ablated tissue was analyzed in real-time mode by means of spectroscopy. Each laser pulse produced one spectrum that was characteristic of the composition of the tissue layer, which was ablated. Fluorescence spectroscopy indicated a broad-continuum emission between 300 and 700 nm with peak fluorescence of equal intensity at wavelengths of 370 and 460 nm (ratio, 1.004 + 0.087) for normal media layers. Atheromas without calcification (lipid, fibrous, and mixed) were found with spectral maxima at the same wavelengths but with significantly reduced intensity at 460 nm (ratio, 1.765+± 0.263; p<0.001). In contrast to this broad-continuum fluorescence, calcified plaques displayed multiple-line emission with the most prominent peaks at wavelengths of 397, 442, 450, 461, 528, and 558 nm. These fluorescence criteria identified the histologically classified target tissue precisely. Histological examination of the corresponding arterial layers indicated sharply delineated and circumscribed tissue ablation. These results indicate that simultaneous tissue identification (diagnosis) and ablation (treatment) by excimer laser irradiation is feasible under strict laboratory conditions. We conclude that this principle demonstrates the potential for laser beam control by means of target-specific ablation. (Circulation 1988;78:1031-
A system description and f i s t results of the Asterix I11 high-power iodine laser built at IPP Garching are given. This laser is designed to yield an output energy of 1 kJ in about 1 n s Until now pulses with output energies up to 300 J and pulse lengths ranging from 1 to 3 ns have been obtained.
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