Self-Guiding without Focusing Nonlinearity: Leaking Mode Self-Effect Due to Field-Induced Saturable Ionization
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 experiments1-4 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 waveguide3-5 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 mi, 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.
KeywordsLaser Pulse Ultrashort Laser Pulse Plasma Channel Kerr Nonlinearity Rayleigh Length
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