Measurements of self-guiding of ultrashort laser pulses over long distances

We report on the evaluation of the performance of self-guiding over extended distances with $f/20$ and $f/40$ focussing geometries. Guiding over $39mm$ or more than 100 Rayleigh ranges was observed with the $f/20$ optic at $n_e=1.5\times {10}^{18}{cm}^{-3}$. Analysis of guiding performance found that the extent of the exiting laser spatial mode closely followed the matched spot size predicted by 3D nonlinear theory. Self-guiding with an $f/40$ optic was also characterised, with guided modes observed for a plasma length of $90mm$ and a plasma density of $n_e=9.5\times {10}^{17}{cm}^{-3}$. This corresponds to self-guided propagation over 53 Rayleigh ranges and is similar to distances obtained with discharge plasma channel guiding. (paper)