Institution: | (1) Institut für Physik III, Universität Regensburg, Universitätsstrasse 31, D-8400 Regensburg, Fed. Rep. Germany;(2) National Bureau of Standards, Boulder, Colorado, USA;(3) Laboratoire de Physique des Lasers, Associé au C.N.R.S. L.A. 282, Université Paris-Nord, Avenue J. B. Clément, F-93430 Villetaneuse, France;(4) National Research Council of Canada, Canada;(5) Department of Applied Physics, University of Hull, England |