Abstract

Resonant self-focusing, which occurs in beat-wave excitation of electron plasma waves, is crucial both for multiline laser fusion and for beat-wave accelerators. In this paper, the resonant self-focusing effect of a dual-frequency laser beam or two laser beams with frequency difference equal to the plasma oscillation frequency in a homogeneous plasma has been studied theoretically, for the first time, by using optical mixing and the self-focusing theory. The nonlinear dielectric constant and the threshold power for resonant self-focusing have been derived analytically. The scaling laws of the threshold power with respect to laser-plasma parameters have been discussed and compared with that of usual ponderomotive self-focusing. Otherwise, the effect of the deviation from the frequency matching condition on the threshold power has also been studied. For typical underdense laser-plasma parameters, our estimation shows that the threshold power of resonant self-focusing is usually ~2 orders of magnitude less than that of normal ponderomotive self-focusing. In addition, it is also shown that a small deviation from resonance will result in a large increase in the threshold power.

© 1986 Optical Society of America