MRI: Acquisition of High-Power 100 kHz Laser for Recording Real-Time Movies of Ultrafast Molecular Reactions

预测和控制化学反应结果的能力对于现代物理学、化学和生物学的许多领域都是必不可少的。这种能力需要详细了解分子中的单个原子如何在反应过程中移动以打破，形成或重新排列它们之间的化学键。该研究项目旨在获得这种原子运动的高分辨率电影。由于参与化学反应的原子运动极快，通常在几十飞秒的时间尺度上（一飞秒是十亿分之一秒的百万分之一），超短飞秒激光脉冲是唯一能够在真实的时间内记录这种电影的实验工具。然而，由于原子和分子的量子性质，任何分子反应的结果都不是确定性的：即使一次测量精确地捕获了给定时间所有原子的位置，如果重复多次，即使在完全相同的条件下，相同的测量也会有不同的结果。获得每秒提供10万个脉冲（每个脉冲短于10飞秒）的高功率激光系统将能够重复数百万次这样的测量，这是创建量子力学分子电影所需的。电影的每一帧都反映了反应不同阶段原子的每一种可能构型的概率，而不是一个分子的固定图像。这些电影将促进我们对基本化学过程的理解，并为国家优先领域的应用提供投入，从有效的能量转换和储存到新型材料的合成，药物设计和分子电子学。 该项目由主要研究仪器计划和刺激竞争研究的既定计划（EPSCoR）共同资助。在这一项目范围内，将研究一系列广泛的光化学过程，包括光解离和异构化、电荷转移反应和货车德瓦耳斯团簇的形成。对于这些过程中的每一个，主要的科学目标是成像随时间变化的分子几何形状，同时表征分子的演变电子结构。这将通过采用几种互补的时间分辨技术来实现，包括光电子能谱和离子动量成像、内壳层和激光诱导光电子衍射以及离子束技术和傅里叶变换能谱来表征中性碎片。对于所有这些技术，促进电子和核自由度的同时表征的关键技术方面将是几个反应产物的同时检测，通过所获得的激光的高重复率实现。与此同时，它的平均功率高达几百瓦，能够将发射的近红外辐射有效地转换成各种不同的波长（从长波红外线到极紫外线和软X射线）该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的知识产权进行评估来支持。优点和更广泛的影响审查标准。

The ability to predict and control the outcome of chemical reactions is essential for many areas of modern physics, chemistry and biology. This ability requires detailed knowledge of how individual atoms in molecules move to break, form, or rearrange chemical bonds between them during the reaction. This research project aims at obtaining high-resolution movies of such atomic motion. Since the atoms involved in chemical reactions move extremely fast, typically on a time scale of few tens of femtoseconds (one femtosecond is one millionth of a billionth of a second), ultrashort, femtosecond laser pulses are the only experimental tools capable of recording such movies in real time. However, because of the quantum nature of atoms and molecules, the outcome of any molecular reaction is not deterministic: even if one measurement precisely captures the positions of all atoms at a given time, the same measurement will have different outcomes if repeated several times, even under exactly identical conditions. The acquisition of a high-power laser system delivering a hundred thousand pulses (each shorter than 10 femtoseconds) per second will enable repeating such measurements millions of times, which is needed for the creation of a quantum-mechanical molecular movie. Each frame of a movie then reflects the probability of every possible configuration of atoms at different stages of the reaction, instead of a fixed picture of a molecule. Such movies will advance our understanding of fundamental chemical processes and provide input for applications in areas of national priority, ranging from efficient energy conversion and storage to synthesis of novel materials, drug design and molecular electronics. This project is jointly funded by the Major Research Instrumentation program and the Established Program to Stimulate Competitive Research (EPSCoR). Within this project, a broad range of photochemical processes, including photodissociation and isomerization, charge transfer reactions and formation of van der Waals clusters, will be studied. For each of these processes, the main scientific goal is to image the time-dependent molecular geometry and simultaneously characterize the evolving electronic structure of the molecule. This will be achieved by employing several complementary time-resolved techniques, including photoelectron spectroscopy and ion momentum imaging, inner-shell and laser-induced photoelectron diffraction, as well as ion beam techniques and Fourier-transform spectroscopy for characterization of the neutral fragments. For all these techniques, the key technical aspect facilitating simultaneous characterization of electronic and nuclear degrees of freedom will be the coincident detection of several reaction products, enabled by the high repetition rate of the acquired laser. At the same time, its high average power of several hundred watts will enable the efficient conversion of the emitted near-infrared radiation to a broad range of different wavelengths (from long-wavelength infrared to extreme ultraviolet and soft x-rays) needed for initiating and probing the reactions to be studied.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.