Nonlocal effects and the Raman instability

The full Raman scattering equations have been solved in a linear density profile in an attempt to overcome the local nature of most previous analyses. The global solution obtained elucidates the transition between absolute and convective Raman instabilities. Feedback linking backward and forward Raman scattering can result in an instability that is absolute at all scattered frequencies. Moreover, thresholds for this absolute instability are lower by a factor of 4 than those for the convective instability where backward and forward scattering are treated as independent events.