(1) Center for Ultrafast Optical Science, University of Michigan, Ann Arbor, MI 48109-2099, USA (Fax: +313/763-4876; E-mail: kapteyn@umich.edu), US;(2) Department of Physics, Sofia University, Sofia, Bulgaria, BG
Abstract:
Received: 28 April 1997/Revised version: 15 May 1997