Malkin V M, Fisch N J
Princeton University, Princeton, New Jersey 08544, USA.
Phys Rev E Stat Nonlin Soft Matter Phys. 2009 Oct;80(4 Pt 2):046409. doi: 10.1103/PhysRevE.80.046409. Epub 2009 Oct 29.
New powerful soft x-ray sources may be able to access intensities needed for backward Raman amplification (BRA) of x-ray pulses in plasmas. However, high plasma densities, needed to provide enough coupling between the pump and seed x-ray pulses, cause strong damping of the Langmuir wave that mediates energy transfer from the pump to the seed pulse. Such damping could reduce the coupling, thus making efficient BRA impossible. This work shows that efficient BRA can survive despite the Langmuir wave damping significantly exceeding the linear BRA growth rate. Moreover, the strong Langmuir wave damping can automatically suppress deleterious instabilities of BRA to the thermal noise. The class of "quasitransient" BRA regimes identified here shows that it may be feasible to observe x-ray BRA within available x-ray facilities.
新型强大的软X射线源或许能够达到等离子体中X射线脉冲后向拉曼放大（BRA）所需的强度。然而，为了在泵浦X射线脉冲和种子X射线脉冲之间提供足够的耦合而需要的高等离子体密度，会导致介导从泵浦脉冲到种子脉冲能量转移的朗缪尔波出现强烈阻尼。这种阻尼会降低耦合，从而使得高效的BRA无法实现。这项工作表明，尽管朗缪尔波阻尼显著超过线性BRA增长率，高效的BRA仍可实现。此外，强烈的朗缪尔波阻尼能够自动抑制BRA对热噪声的有害不稳定性。这里所确定的“准瞬态”BRA机制表明，在现有的X射线设施内观测X射线BRA可能是可行的。
