Abstract: Nonlinear absorption of a sub-picosecond laser pulse is used to generate one or more spatially elongated heated gas volumes. Transient density variations caused by the spatially elongated heated gas volumes provide a refractive index profile capable of guiding electromagnetic radiation through the gas. The waveguide structure in the gas is disposed between the spatially elongated heated gas volumes and results from interaction between acoustic waves generated by the spatially elongated heated gas volumes or from a non-uniform thermal gas profile caused by the spatially elongated heated gas volumes. The nonlinear absorption can be repeated at regular intervals in time and space to renew the waveguide in the gas, thereby allowing for the guiding of high average power radiation (e.g., megawatts) that is well below self-focusing or stimulated Raman scattering thresholds.