等离子体密度对激光拉曼放大机理的影响  

Plasma density effect on backward Raman laser amplification

作　　者：张智猛[1] 张博[1] 吴凤娟[1,2] 洪伟[1] 滕建[1] 贺书凯[1] 谷渝秋[1,3] 

机构地区：[1]中国工程物理研究院激光聚变研究中心等离子体物理重点实验室,绵阳621900 [2]西南科技大学国防科技学院,绵阳621010 [3]北京大学应用物理与技术研究中心,北京100088

出　　处：《物理学报》2015年第10期123-128,共6页Acta Physica Sinica

基　　金：国家自然科学基金(批准号:11305157);等离子体重点实验室基金(批准号:9140C680604130C68245)资助的课题~~

摘　　要：等离子体中的背向拉曼散射机理可以用来产生超短超强的激光脉冲.本文采用粒子模拟方法模拟研究了等离子体密度对激光拉曼放大过程的影响.研究发现,过低的等离子体密度会导致等离子体波提前波破而降低能量转换效率;而过高的等离子体密度又会导致其他不稳定性的快速增长,限制作用距离和输出能量.因此,拉曼放大机理的最佳等离子体密度应处于等离子体波破的密度阈值附近,可以获得最高的能量转换效率和能量输出.另外,空间频谱分析显示放大激光的强度饱和主要来自于自相位调制不稳定性的发展.利用1013W·cm-2的抽运激光脉冲,模拟证实拉曼放大机理可有效地将种子激光的强度从1013W·cm-2放大到1017W·cm-2,脉宽压缩到40 fs,且能量转换效率达到58%.Backward Raman amplification （BRA） in plasma can be used for generating ultra-powerful laser pulses. In this paper, the plasma density effect on backward Raman laser amplification is studied by using particle-in-cell method, It is found that using a low plasma density can lead to the premature Langmuir wave breaking and thus result in a small energy-transfer efficiency. On the other hand, using a high plasma density will enhance the developments of unwanted instabilities, which rapidly disturb the Raman amplification, thus limiting the interaction length and output power, Therefore, an optimal plasma density for BRA is near the threshold of Langmuir wave breaking in order to achieve both high efficiency and large energy flux. The space frequency spectrum analysis shows that the saturated Intensity of amplified pulses is limited mainly by the self-phase modulation instability. By using a 1013 W·cm-2 pump pulse, our simulation results show that the initial 1013 W·cm-2 seed pulse can be well be well amplified into a pulse with an energy power of 1017 W·cm-2, a duration of 40 fs, and and an energy conversion efficiency of up to 58%.

关 键 词：超短超强激光 激光放大 拉曼向后散射 粒子模拟 

分 类 号：O53[理学—等离子体物理]