We report on the use of a novel technique to create a plasma waveguide suitable for guiding high-intensity laser pulses in underdense plasmas. A narrow channel of a clustering gas is dissociated with a low-intensity prepulse. This prepulse is followed by a high-intensity, focused laser pulse. The high absorption of the clusters surrounding the dissociated atomic channel causes the remaining annulus of clusters to become highly ionized, leaving low-density plasma in the center. We have interferometrically probed the formation of this channel with picosecond laser pulses. (C) 1998 Optical Society of America. [References: 13]
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