Nonlinear modulational stability and propagation of an electromagnetic pulse in a two-component neutral plasma

Nonlinear effects including possible modulational instability of an intense electromagnetic pulse propagating through a fully ionized unmagnetized plasma are studied. The envelope is shown to evolve over long time scales in general according to a vector form of the well-known cubic nonlinear Schrodinger (NLS) equation. Three distinct nonlinear effects contribute terms cubic in the amplitude and thus can be of comparable magnitude: ponderomotive forces, relativistic corrections and harmonic generation. The calculation takes all three effects into account. Integrability and modulational stability of any given system are shown to depend on polarization, frequency, composition and temperature, and these dependences are given. It is found that finite-temperature effects are qualitatively important only near a critical frequency (<3/2ωp) just above the plasma frequency for which the group velocity is comparable to either (or both) of the sound velocities. The results have important implications for pulsar micropulse observations and possible technological applications. (author)