Attosecond Soft X-ray Spectroscopy of Condensed Phase Matter

该项目将把阿秒X射线吸收光谱技术扩展到凝聚相材料。这将需要进一步优化所需的光源，即“泵浦”和“探测器”，前者是可见至深紫外光范围内的几飞秒长脉冲，后者是100-500 eV光子能量范围内的软X射线孤立阿秒脉冲。对于前者，研究重点将集中在利用非线性光学方法在可见光-近红外区域高效地产生低阶次(高达9次)的少周期脉冲。对于后者，目前的光源基于高密度气体射流中的MIR几个周期脉冲的高次谐波，将通过使用优化的气体射流设计和改善通过光束线的X射线传输来增强。利用这一能力，我们将测量有机聚合物和有机低聚物在液体中的激子动力学，以更好地了解激子在这些材料中退相干和输运的基本问题。将系统地探索聚合物结构和样品形态的作用。这样，这项研究不仅将进一步发展超快X射线测量工具，而且还可能有助于理解目前用于太阳能收集研究的聚合物光电子中的重要材料。

The project will extend the technique of attosecond X-ray absorption spectroscopy to condensed phase materials. This will require further optimization of the required optical sources i.e. both the "pump" which are few-femtosecond long pulses in the visible to deep UV range, and the "probe" which are soft X-ray isolated attosecond pulses in the 100 - 500 eV photon energy range. For the former the research will focus on using non-linear optical methods to efficiently generate low order (up to 9th) of few-cycle pulses in the visible-NIR region. For the latter the present source, based on HHG of MIR few-cycle pulses in high density gas jets, will be enhanced by the use of optimized gas jet design and improved X-ray transmission through the beamline. With this capability we will measure exciton dynamics in organic polymers and organic oligomers in liquid phase to better understand fundamental issues of decoherence and transport of excitons in these materials. The role of polymer structure and morphology of the samples will be systematically explored. In this way not only will the research further the tools of ultrafast X-ray measurement, but may also contribute to the understanding of important materials in polymer opto-electronics that are currently used in solar energy harvesting research.