Modulational instability and beam splitting in the nonlinear light propagation in sodium vapour

T. Ackemann, A. Aumann, Yu A. Logvin

Research output: Contribution to journalArticlepeer-review

4 Citations (Scopus)


A linearly polarized laser beam propagating through sodium vapour is known to break up into its circular polarization components ('beam splitting'). We clarify the underlying mechanism by showing that spatially periodic perturbations of the polarization state of a plane wave will be amplified exponentially during propagation due to a modulational instability. For a Gaussian beam in one transverse spatial dimension we find even as well as odd active eigenmodes for polarization perturbations. Their two-dimensional generalizations elucidate the reason for the radial and lateral splitting that is observed in a number of experiments. In the limiting case of a cubic nonlinearity the splitting can also be expected from a variational approach.

Original languageEnglish
Pages (from-to)90-95
Number of pages6
JournalJournal of Optics B: Quantum and Semiclassical Optics
Issue number6
Publication statusPublished - 1 Dec 1999


  • nonlinear wave propagation
  • polarization competition
  • polarization patterns
  • solitons
  • cavity solitons
  • solitary waves
  • modulational instability
  • beam splitting
  • nonlinear light propagation
  • sodium vapour


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