Abstract

Creation of elongated plasma structures for guiding of powerful ultra-short laser pulses is a challenging scientific problem and an important application in the area of superstrong field interaction with matter. Self-channeling regimes recently observed in experiments^1-4 have been attributed to the focusing nature of relativistic and Kerr nonlinearities that cause an increase of the refractive index and deviation of light rays toward stronger field regions. In the case of gas ionization at the axis of a Kerr-effect induced waveguide^3-5 the influence of focusing nonlinearity should be especially strong since it is not only to prevent the divergence of rays due to linear diffraction but also to balance refraction of radiation from the axis, that is caused by emerging plasma. Experimentally observed extra-long waveguides produced by few mJ, 100 fs laser pulses at ionization of atmospheric air³,⁴ have been interpreted as plasma structures having a core where the ionization nonlinearity prevails and an outer cladding where the dominating Kerr nonlinearity generates opposite-in-sign positive variations of the refractive index and hence keeps the radiation from divergence.

© 1997 Optical Society of America