New high harmonic generation mechanism

我研究了多太瓦飞秒激光的高次谐波产生的新制度，聚焦到强度I_0>1e18 W/cm2的气体喷射目标。我确定了光谱特性、角分布、相干性和源尺寸。在日本原子能机构（JAEA）的9tw J-KAREN激光器实验中，谐波辐射的光子能量达到360 eV，在“水窗”光谱区域内。我提出并证明了相对论性电子尖峰产生谐波的新模型，它是由多流相对论性等离子体流的突变引起的密度奇点。这一结果可能为下一代明亮紧凑的相干x射线源开辟了一条道路，这种x射线源可以建立在大学实验室规模的重复激光和可访问的、可补充的、无碎片的气体喷射目标上。这将影响许多基础研究和应用领域，这些领域需要明亮的x射线源来进行泵送、探测、成像或阿秒科学。

I studied a new regime of high-order harmonic generation in the interaction of multi-terawatt femtosecond lasers focused up to intensity I_0>1e18 W/cm2 into gas jet targets. I determined spectral properties, angular distribution, coherence, and source size. In experiments with the 9 TW J-KAREN laser in Japan Atomic Energy Agency (JAEA), the photon energy of harmonic radiation reached 360 eV, within the "water window" spectral region. I suggested and justified a new model of harmonic generation by relativistic electron spikes, which are density singularities resulting from catastrophes of a multi-stream relativistic plasma flow.The results may open a way toward a next-generation bright compact coherent x-ray source which can be built on a university-lab-scale repetitive laser and accessible, replenishable, debris-free gas jet target. This will impact many areas of fundamental research and applications requiring a bright x-ray source for pumping, probing, imaging, or attosecond science.