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x射线源的范围，从基于强烈激光等离子体相互作用的源中产生数千伏的明亮超快x射线。该研究涉及在相对论极限下，利用倍频辐射和高谐波产生（HHG）的机制进行超快（飞秒）x射线的实验产生、测量和建模。第一种机制是利用等离子体加速器聚焦场中加速电子的倍频振荡，产生跨越千伏特百伏特窗口的强宽带非相干x射线。在第一阶段的工作中，该电子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。这些知识和专长将在项目的第二阶段应用于HHG。其次，提出了一种利用相对论强度的多个激光脉冲将相干x射线HHG扩展到多千伏范围的新方法。当一个电子从宿主原子中电离出来，然后被激光场驱动回去与宿主原子重新结合时，HHG就会发生。在传统的单脉冲方案中，光子能量受到等离子体诱导退相干的限制，从而限制了有效相互作用的长度。对于相对论性强度，电离电子与激光场的磁相互作用通过阻止电子与原子重新结合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，创造一个离子通道，并且，通过使用两个反传播脉冲，磁场诱导的电子漂移将被消除。这将把紧凑的相干HHG源的覆盖范围从0.5千伏（目前最先进的）扩展到100千伏甚至更高。

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.