Propagation of intense ultrashort laser pulses in a plasma filled capillary tube: Simulations and experiments

Recent experiments [F. Dorchies et al., Phys. Rev. Lett. 82, 4655 (1999)] have demonstrated monomode guiding over 100 Rayleigh lengths (10 cm) of high intensity, ultrashort laser pulses in a dielectric capillary tube filled with low pressure He gas. A model for the propagation of femtosecond laser pulses in a capillary tube, coupled with the tunnel ionization of the gas filling the capillary tube, is derived and solved numerically using the parameters of these experiments. The simulations accurately reproduce experimentally measured damping lengths, transmitted pulse energy and spectrum at the output of the capillary tube. They show that a few cm long, homogeneous, plasma column with an electron density of the order of 10¹⁷ cm^-3 is created for an incident intensity of 4 × 10¹⁵ W/cm².