Control of density correlations in laser-heated plasma

The excitation of plasma density perturbations of selected wavenumber spectra by two oppositely directed short-wavelength laser beams and the simultaneous interaction with these perturbations of a long-wavelength laser beam whose frequency is comparable to the electron Langmuir frequency is analyzed. Perturbations of the plasma density having a spatial period equal to one-half the wavelength of the short-wavelength beams are produced at zero frequency, and at the ion-acoustic frequency. The third beam excites the oscillating two-stream instability and the ion-acoustic decay instability, so that these initial perturbations will grow rapidly and dominate the density fluctuation spectrum. The present scheme may be useful in avoiding superthermal electrons that are typically produced when radiation from a single beam is absorbed and long-wavelength density fluctuations become significant.