Tuneable Femtosecond Laser Sources for Time-Resolved Ultrafast Spectroscopy

用于时间分辨超快光谱的可调谐飞秒激光源

• 批准号: RTI-2022-00316
• 负责人: Stolow, Albert
• 金额: $ 8.53万
• 依托单位: University of Ottawa
• 依托单位国家: 加拿大
• 项目类别: Research Tools and Instruments
• 财政年份: 2021
• 资助国家: 加拿大
• 起止时间: 2021-01-01 至 2022-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=743054
• 关键词: Tuneable; Femtosecond; Laser; Sources; Time

The ultrafast dynamical motions of electrons within molecules and materials underlies the fundamental processes of photosynthesis, vision and solar energy conversion (photovoltaics). Electronic charge transfer necessarily involve the coupling of electronic with vibrational motions. These non-adiabatic (non-Born-Oppenheimer) processes, which take place on the time scales of 10's of fs, are ubiquitous in electronically excited molecular states. Examples include charge transfer, isomerization and photochemical reaction. Despite this fundamental importance, ultrafast electronically non-adiabatic dynamics remains one of the most challenging problems in Physical Chemistry. While employed at the NRC (1992-2014), Dr. Stolow pioneered the powerful technique of fs Time-Resolved Photoelectron Spectroscopy (TRPES) which permits the disentangling of coupled electronic-vibrational dynamics in electronically excited molecules. The method is based on resonantly exciting a molecule with a tuneable fs pump pulse and then photoionizing the evolving excited state with a delayed tuneable fs probe pulse. The resulting energy-angle-time resolved photoelectron spectrum demonstrably contains a wealth of details about excited state electronic processes and their non-adiabatic coupling. Although originally based at the NRC, Stolow's program fully transitioned to uOttawa in Fall 2021. Hence, the need for NSERC-supported tuneable fs lasers which do not exist at uOttawa. Stolow's NSERC-supported TRPES technique requires that two independently tuneable fs pump and probe pulses in the UV or VUV ranges be generated with sufficient pulse energy. Each molecule under study has specific resonant transitions and the pump laser must therefore be tuned to that molecule. Likewise, since Ionization Potentials also vary, an independently tunable fs probe laser pulse is also required. This RTI request is therefore for two independent but synchronized `Light Conversion' TOPAS Optical Parametric Amplifiers which provide broadly tuneable fs pulses. One of these must have higher energy output in order to permit the less efficient generation of fs VUV pulses. This RTI benefits from an existing femtosecond Ti:Sa (i.e. non-tuneable, 800 nm) pump laser and optical table installed at uOttawa. The requested TOPAS systems are essential for the continuation of Dr. Stolow's TRPES research program at uOttawa: without the ability to broadly tune fs laser pulses, this TRPES research program cannot effectively continue. The requested TOPAS units will be used in each and every TRPES experiment (> 80 hours/month) and will play a central role in the training of HQPs in nonlinear optics and ultrafast spectroscopy: they will be routinely used by all students.

分子和材料内电子的超快动态运动是光合作用、视觉和太阳能转换（光伏）基本过程的基础。电子电荷转移必然涉及电子与振动运动的耦合。这些非绝热（非玻恩-奥本海默）过程发生在 10 飞秒的时间尺度上，在电子激发分子态中普遍存在。例子包括电荷转移、异构化和光化学反应。尽管具有这一根本重要性，超快电子非绝热动力学仍然是物理化学中最具挑战性的问题之一。在 NRC 工作期间（1992-2014 年），Stolow 博士开创了飞秒时间分辨光电子能谱 (TRPES) 的强大技术，该技术可以解开电子激发分子中耦合的电子振动动力学。该方法基于用可调谐飞秒泵浦脉冲共振激发分子，然后用延迟可调谐飞秒探测脉冲对不断变化的激发态进行光电离。由此产生的能量-角度时间分辨光电子谱显然包含有关激发态电子过程及其非绝热耦合的大量细节。尽管斯托洛的项目最初位于 NRC，但已于 2021 年秋季完全转移到渥太华大学。因此，需要 NSERC 支持的可调谐飞秒激光器，而渥太华大学并不存在。 Stolow 的 NSERC 支持的 TRPES 技术要求以足够的脉冲能量生成 UV 或 VUV 范围内的两个独立可调的 fs 泵浦和探测脉冲。所研究的每个分子都有特定的共振跃迁，因此必须将泵浦激光器调谐到该分子。同样，由于电离势也会变化，因此还需要独立可调谐的 fs 探针激光脉冲。因此，该 RTI 请求是针对两个独立但同步的“光转换”TOPAS 光学参量放大器，它们提供广泛可调的 fs 脉冲。其中之一必须具有更高的能量输出，以允许较低效率地生成飞秒 VUV 脉冲。该 RTI 受益于渥太华大学安装的现有飞秒 Ti:Sa（即不可调谐，800 nm）泵浦激光器和光学平台。所要求的 TOPAS 系统对于 Stolow 博士在渥太华大学的 TRPES 研究计划的继续至关重要：如果没有广泛调谐飞秒激光脉冲的能力，该 TRPES 研究计划就无法有效地继续。所要求的 TOPAS 装置将用于每个 TRPES 实验（> 80 小时/月），并将在非线性光学和超快光谱学 HQP 培训中发挥核心作用：它们将被所有学生常规使用。