MODE CONTROL IN A 2-PULSE-EXCITED PLASMA WAVE-GUIDE

We demonstrate that the application of a second excitation pulse to a laser-driven plasma waveguide [Phys. Rev. Lett. 71, 2409 (1993)] stron gly influences the propagation of a guided probe pulse and offers furt her opportunity for mode control beyond that already demonstrated [Opt . Lett. 19,1937 (1994)]. Under the conditions of leaky-mode propagatio n, the second excitation pulse promptly enhances the guided pulse tran smission by driving the channel's electron density barrier to increase d height and thickness. The second excitation pulse also induces an in wardly directed compression wave in the channel, so that the guided pu lse spot size is observed to decrease for early delays after the arriv al of the second pulse. Guiding in a low-order mode is inhibited as th is compression wave :reaches the channel center but resumes at later t imes, as the channel center density relaxes. (C) 1996 Optical Society of America