Stimulated Raman backscatter in ultraintense, short pulse laser–plasma interactions

The stimulated Raman backscatter instability that occurs when short (∼50–100 fs), intense (I≂2×1017 W/cm2) laser pulses are focused into a high density, low temperature plasma is reported on in this article. Results from linear theory, numerical differencing of the coupled mode equations, and one-dimensional particle-in-cell simulations will be discussed. It is found that the growth rate is a function of position along the pulse, and that the maximum growth rate at the peak of the pulse is reduced from the homogeneous long pulse value, γ0 by a factor of 1/√2. A criterion is obtained that predicts when the product of the pulse length and the growth rate is large enough so that the backscatter instability will heat the background electrons to a significant amount above the initial temperature. The usual hot electron component associated with this instability will also be discussed.