Waveform Synthesis of Attosecond Optical Pulses: A Common Route to Attosecond Pump-Probe Spectroscopy and Nanoscopy in Aqueous Solution

当分子吸收光时，它的电子云几乎瞬间发生反应，随后在飞秒(fs=10-15s)内发生旋转核动力学。至皮秒(PS=10-12s.)时间刻度。例如，在光合作用中，叶绿素分子对紫外光的吸收引起电子偶极振荡，其周期在1飞秒范围内，随后其较慢的衰减和能量重新分配到核的自由度。在过去的几十年里，时间分辨光谱学展示了几个周期的飞秒激光脉冲可以用来引导核波包和控制基本反应的结果。然而，由于缺乏更短的脉冲，使得对亚振荡周期时间尺度上的电子波包的控制还没有被探索出来。是否有可能从电子偶极力启动核运动的最早时刻就跟踪并最终更有效地控制反应动力学？*新兴的阿托秒物理学领域为这些问题提供了新的视角。事实上，无论是孤立的极端紫外线(XUV，10-100 eV)还是宽带光学阿秒(AS=10-18 S)。脉冲可以与普通的桌面飞秒光学技术同时产生和同步。最近的激光发展甚至将XUV的阿秒辐射扩展到“水窗”软X射线(280-500 eV)甚至更高。这一壮举从根本上偏离了迄今为止只有大规模(0.1-10公里)加速器设施才能获得的最短皮秒脉冲。水窗口指定了水基本上对辐射透明，而碳和氮原子具有高度吸收的光谱范围；实现了水中新颖的高对比度、特定元素、时间分辨率的光谱和纳米技术。将我在时间分辨分子光谱学方面的经验(渥太华大学博士，主任：Paul Corkum)与加拿大在阿秒技术和光学波形合成方面的独特专业知识(2013-2014年慕尼黑Max-Planck-Institute for Quantum Optics，主任：Ferenc Krausz)相结合，我的研究小组有一个长期的愿景：*通过实施提供光学和水窗口软X射线阿秒脉冲的光学波形合成，使生物分子在水溶液中具有未知的时间和空间分辨率。*我们将有：*1)演示了产生相干软X射线水窗辐射的光学波形合成。*2)使用这种辐射在未探索的阿秒范围内对水相中的分子进行光谱分析。*3)使用超短波长的相干软X射线(2-10 nm)在空间上解析纳米结构。*这项跨学科研究将培养高素质的人才，并为新技术在健康科学中的应用开辟道路。

When a molecule absorbs light, its electronic cloud reacts almost instantaneously followed by rovibrational nuclear dynamics on the femtosecond (fs=10-15s.) to picosecond (ps=10-12s.) timescale. In photosynthesis, for example, the absorption of ultraviolet light by chlorophyll molecules induces an electronic dipole oscillation, which has a period in the range of 1 fs, followed by its slower decay and energy redistribution to the nuclear degrees of freedom. Over the last decades, time-resolved spectroscopy showed how few-cycle femtosecond laser pulses can be used to steer nuclear wave packets and control the outcome of elementary reactions. The lack of shorter pulses, however, has left control of the electron wave packets on the sub-oscillation period timescale unexplored. Would it be possible to follow and, ultimately, more efficiently control reaction dynamics right from the earliest moments when electron dipole forces initiate nuclear motion?****The emerging field of Attosecond Physics offers a new take on these questions. In fact, both isolated extreme ultraviolet (XUV, 10-100 eV) and broadband optical attosecond (as=10-18 s.) pulses can be simultaneously produced and synchronized with common tabletop femtosecond optical technology. Recent laser developments even extend the attosecond emission from the XUV to "water window" soft X-rays (280-500eV) and beyond. This feat radically departs from the shortest picosecond pulses so far only available from large scale (0.1-10 km) accelerator facilities. The water window designates the spectral range where water is essentially transparent to the radiation while carbon and nitrogen atoms are highly absorptive; enabling novel high-contrast, element-specific, time-resolved spectroscopy and nanoscopy in water. Combining my experience in time-resolved molecular spectroscopy (Ph.D, University of Ottawa, director: Paul Corkum) with a unique -in Canada- expertise in attosecond technology and optical waveform synthesis (Banting postdoctoral fellowship at the Max-Planck-Institut for Quantum Optics in Munich, 2013-2014, director: Ferenc Krausz), my research group has the long term vision:***To make possible the spectroscopy of biomolecules in aqueous solution with unexplored time and spatial resolutions through the implementation of optical waveform synthesis providing both optical and water window soft X-ray attosecond pulses.***By the end of year 5, we will have:***1) Demonstrated optical waveform synthesis to generate coherent soft X-ray water window radiation. ***2) Used this radiation for the spectroscopy of molecules in aqueous phase in unexplored attosecond regime.***3) Used the ultrashort wavelength of coherent soft X-rays (2-10 nm) to spatially resolve nanometric structures.***This interdisciplinary research will train highly qualified personnel and open avenues for new technological applications in health sciences.*** *** *** **