Multi-keV x-ray production by high harmonic generation using ultra-intense lasers

该项目致力于开发两种技术，以扩展紧凑型X射线源的范围，从基于强烈激光等离子体相互作用的源产生多千伏级的明亮超快X射线。该研究涉及在相对论极限下使用电子感应加速器辐射和高次谐波产生（HHG）机制的超快（飞秒）X射线的实验产生，测量和建模。第一种机制使用加速电子在基于等离子体的加速器的聚焦场中的电子感应加速器振荡来产生跨越千伏百千伏窗口的强烈宽带非相干x射线。在工作的第一阶段，该电子感应加速器辐射源将用于测试，校准和现场X射线诊断，以表征该范围内的辐射。这些知识和专业知识将在该计划的第二阶段应用于HHG。第二，发展了一种利用多个相对论强度的激光脉冲将相干X射线高次谐波谱扩展到数千伏范围的新方法。高次谐波发生在电子从宿主原子电离，然后被激光场驱动回与原子复合时。 在传统的单脉冲方案中，光子能量受到等离子体诱导的退相干的限制，这限制了有效的相互作用长度。对于相对论强度，电离电子与激光场的磁相互作用通过防止电子与原子重新结合而进一步抑制辐射的产生。 一个强激光将被用来驱逐等离子体电子创建一个离子通道，并通过使用两个反向传播脉冲，磁场诱导的电子漂移将被删除。这将使紧凑型相干HHG源的范围从0.5千伏（当前最先进的）扩展到潜在的100千伏及以上。

This project addresses the development of two techniques to extend the reach of compact x-ray sources, producing bright, ultrafast x-rays in the multi-kilovolt regime from sources based on intense laser-plasma interaction. The research involves the experimental generation, measurement and modeling of ultrafast (femtosecond) x-rays using the mechanisms of betatron radiation and high harmonic generation (HHG) in the relativistic limit. The first mechanism uses the betatron oscillation of accelerated electrons in the focusing field of a plasma-based accelerator to generate intense broad-bandwidth incoherent x-rays spanning the kilovolt hundred kilovolt window. In the first phase of the work this betatron radiation source will be used to test, calibrate, and field x-ray diagnostics required to characterize the radiation in this range. This knowledge and expertise will be applied to HHG in the second phase of this program. Secondly, a new method for extending coherent x-ray HHG into the many-kilovolt regime by using multiple laser pulses of relativistic intensity will be developed. HHG occurs when an electron is ionized from a host atom and is then driven back to recombine with the atom by the laser field. Photon energy is limited in conventional single-pulse schemes by plasma-induced decoherence, which limits the effective interaction length. For relativistic intensities, the magnetic interaction of the ionized electron with the laser field further suppresses radiation generation by preventing the electron from recombining with the atom. An intense laser will be used to expel plasma electrons creating an ion channel, and, by using two counterpropagating pulses, the magnetic-field induced drift of the electron will be removed. This will extend the reach of compact coherent HHG sources from 0.5 kilovolt (current state-of-the-art) to potentially 100 kilovolt and beyond.