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

阿秒光脉冲的波形合成：水溶液中阿秒泵浦探针光谱学和纳米显微镜学的共同途径

• 批准号: RGPIN-2015-06208
• 负责人: BeaudoinBertrand, Julien
• 金额: $ 2.4万
• 依托单位: Université Laval
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2016
• 资助国家: 加拿大
• 起止时间: 2016-01-01 至 2017-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=614006
• 关键词: Waveform; Synthesis; Attosecond; Optical; Pulses

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.

当分子吸收光时，其电子云几乎立即发生反应，随后在飞秒（fs=10-15s.）到皮秒（ps=10-12s.）时间尺度上发生旋转核动力学。例如，在光合作用中，叶绿素分子吸收紫外线会引起电子偶极子振荡，其周期在 1 fs 范围内，随后衰减较慢，能量重新分配到核自由度。在过去的几十年里，时间分辨光谱显示了如何使用少周期飞秒激光脉冲来引导核波包并控制基本反应的结果。然而，由于缺乏较短的脉冲，使得亚振荡周期时间尺度上的电子波包的控制尚未被探索。是否有可能从电子偶极力引发核运动的最早时刻开始跟踪并最终更有效地控制反应动力学？ 阿秒物理学的新兴领域为这些问题提供了新的视角。事实上，隔离极紫外（XUV，10-100 eV）和宽带光学阿秒（as=10-18 s.）脉冲可以同时产生并与常见的桌面飞秒光学技术同步。最近的激光发展甚至将阿秒发射从 XUV 扩展到“水窗”软 X 射线（280-500eV）及以上。这一壮举与迄今为止只能从大型（0.1-10 公里）加速器设施获得的最短皮秒脉冲截然不同。水窗指定了水对辐射基本上透明而碳和氮原子具有高度吸收性的光谱范围；在水中实现新颖的高对比度、元素特异性、时间分辨光谱和纳米显微镜。将我在时间分辨分子光谱方面的经验（渥太华大学博士，主任：Paul Corkum）与在加拿大独特的阿秒技术和光学波形合成专业知识（2013-2014 年在慕尼黑马克斯普朗克量子光学研究所班廷博士后奖学金，主任：Ferenc Krausz）相结合，我的研究小组有长期愿景： 通过提供光学和水窗软 X 射线阿秒脉冲的光学波形合成，使水溶液中生物分子的光谱分析成为可能，具有未开发的时间和空间分辨率。 到第 5 年年底，我们将： 1) 演示了光学波形合成以产生相干软 X 射线水窗辐射。 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）利用相干软X射线的超短波长（2-10 nm）来空间解析纳米结构。 这项跨学科研究将培养高素质人才，并为健康科学新技术应用开辟途径。