It is demonstrated by experiments and supporting particle simulations that the forward Raman instability is capable of producing extremely high-energy electrons in an underdense plasma. The instability has a high saturation level for the electrostatic wave component. Its consequences and applications to the laser electron accelerator and the laser-fusion pellet preheat are discussed.

Hot electron generation in a long-density-scale-length (~300 pirn) underdense plasma has been studied. For a plasma of maximum electron density of \n c the hot electron emission is localized in the plane of polarization of the incident C0 2 laser and peaked about 45° with respect to the k vector of the laser beam, in both forward and backward directions. These observations suggest that the hot electrons are generated by the twoplasmon decay instability at quarter-critical density.

Experimental results are presented to demonstrate the principle of electron acceleration by relativistic electron plasma waves driven by the optical mixing of laser light in a plasma. Electrons injected at 12.5 MeV have been accelerated to 29.0 MeV over a plasma length of approximately 1 cm. This corresponds to an effective accelerating electric field gradient of approximately 1.7 GeV/m.

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Experimental studies of stimulated Raman back and side scattering, two-plasmon decay, and the generation of high-energy electrons in 0.35 μm laser plasma interaction are presented. To isolate the various phenomena occurring at different densities, we have attempted to control the maximum plasma density by varying the thickness of the foil targets. The scattered light frequency is used as a diagnostic to measure the peak plasma density. Time integrated and time resolved scattered spectra for variable plasma densities are discussed. Effects of self-generated magnetic fields and plasma temperature on SRS and 2ωp decay, respectively, are examined as possible mechanisms responsible for splitting of the backscattered spectrum at ω0/2. A discussion of the effects of a parabolic density profile on the SRS threshold is also included. Finally, the measured energy and angular distribution of the high-energy electrons are discussed. Two-plasmon decay is suggested as the probable mechanism generating the hot electrons.