Plasma line emission is observed in simulations of dense plasma irradiated by moderately intense light pulses of duration some tens of femtoseconds, and its scaling with density and with laser intensity is studied. Plasma emission is recorded both during the pulse where it is observed against the background spectrum of harmonics of the laser frequency as well as postpulse. Harmonics of the plasma line up to the fifth have been observed. An unexpected feature present in most of the reflected light spectra appears on the blue side of the plasma line with a central frequency omega approximately 1.5omega(p).

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The nonlinear interaction of three and four waves in a warm magnetized plasma is studied using the Lagrangian formalism. General expressions for the coupling coefficients are obtained in each case. Coupled-mode equations describing four-wave interactions have been derived and solved. The extension of the theory to the interaction of random phase waves and weak inhomogeneity is also discussed.

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A model of stimulated Raman scattering from underdense plasmas in which the laser intensity profile and plasma density have been corrupted by the filamentation instability is described. The model accounts in a unified way for inhomogeneity in the density, for Landau damping, and for local enhancements in light-wave intensities. In shallow filaments the concentration of the light gives rise to modest increases in growth. On the other hand, for deeper filaments the inhomogeneity and Landau damping dominate to suppress the instability. In addition, backscatter is enhanced relative to sidescatter.

The effects of a magnetic field on the Raman and two-plasmon decay instabilities are studied in the region of the quarter-critical density of laser produced plasmas where both are coincident. Two-plasmon decay of the incident extraordinary wave into two upper-hybrid waves may now occur in the direction of propagation of the incident radiation driven by the electrostatic component of the extraordinary mode. Maximum growth rates of both the Raman and two-plasmon decay instabilities are increased by the magnetic field. For the two-plasmon decay, the frequency shift from ω0/2, where ω0 is the frequency of the incident radiation, is increased by the magnetic field by amounts which can exceed the thermal shift. This magnetic shift derives from the electromagnetic correction to the dispersion relation of upper-hybrid waves and, consequently, is not found in an electrostatic approximation. For the Raman instability at the reflection point of the scattered extraordinary wave, the red shift of the back-scattered radiation due to the plasma temperature is reduced by any magnetic field present and can be changed to a blue shift if the field is large enough.