Abstract
Plasma waveguides capable of guiding relativistically intense fs laser pulses without optical distortion are essential to developing GeV-scale Laser Wakefield (LWF) Accelerators [1] and coherent short-wavelength sources. We report, to our knowledge, the highest intensity-length product (0.2×1018 W/cm2 × 1.5 cm) to date for distortion-free guiding. We generated our channels in a backfill of He gas (300-700 Torr) using a modification of a method developed by Milchberg et al. [2], who line-focused ~100 ps, ~0.3 J Nd:YAG laser pulses to intensities of ~1013 W/cm2 into a gas using an axicon (see Fig. 1a). This intensity readily field-ionizes high-Z gases (e.g. Ar, N2), thus initiating the channel-forming process, but forms an incompletely-ionized channel, in which relativistically intense pulses suffer ionization-induced phase distortion during guiding and ionization-induced defocusing when entering the channel. Indeed we observe distorted exit mode and spectrum (see Fig. 1c) and only 5% throughput when we attempt to guide a pulse at ≥1017 W/cm2 through a nitrogen channel.
© 2002 Optical Society of America
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