  We demonstrate that femtosecond filaments can set up an extended and robust
thermal waveguide structure in air with a lifetime of several milliseconds,
making possible the very long range guiding and distant projection of high
energy laser pulses and high average power beams. As a proof of principle, we
demonstrate guiding of 110 mJ, 7 ns, 532 nm pulses with 90% throughput over ~15
Rayleigh lengths in a 70 cm long air waveguide generated by the long timescale
thermal relaxation of an array of femtosecond filaments. The guided pulse was
limited only by our available laser energy. In general, these waveguides should
be robust against the effects of thermal blooming of extremely high average
power laser beams.
