Tuneable Femtosecond Laser Sources for Time-Resolved Ultrafast Spectroscopy

电子在分子和物质中的超快动力学运动是光合作用、视觉和太阳能转换（光合作用）的基本过程的基础。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的fs的时间尺度上，是普遍存在的电子激发分子状态。实例包括电荷转移、异构化和光化学反应。尽管有这样的基本重要性，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），Stolow博士开创了fs时间分辨光电子能谱（TRPES）的强大技术，该技术允许在电子激发分子中解开耦合的电子振动动力学。该方法是基于共振激发一个分子与可调飞秒泵浦脉冲，然后光电离的发展与延迟可调飞秒探测脉冲的激发态。由此产生的能量-角度-时间分辨光电子能谱包含了大量关于激发态电子过程及其非绝热耦合的细节。虽然Stolow的计划最初位于NRC，但在2021年秋季完全过渡到uOttawa。因此，需要在uOttawa不存在的NSERC支持的可调谐fs激光器。Stolow的NSERC支持的TRPES技术要求在UV或VUV范围内产生两个独立可调的fs泵浦和探测脉冲，并具有足够的脉冲能量。每一个被研究的分子都有特定的共振跃迁，因此泵浦激光必须被调谐到该分子上。同样，由于电离势也会变化，因此也需要可独立调谐的fs探测激光脉冲。因此，RTI要求两个独立但同步的“光转换”TOPAS光学参量放大器，它们提供宽可调谐fs脉冲。其中之一必须具有较高的能量输出，以允许效率较低的fs VUV脉冲的产生。该RTI受益于现有的飞秒Ti：Sa（即不可调谐的800 nm）泵浦激光器和安装在uOttawa的光学台。所要求的TOPAS系统对于继续Stolow博士在uOttawa的TRPES研究计划至关重要：如果没有广泛调谐fs激光脉冲的能力，这个TRPES研究计划就不能有效地继续下去。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的HQP培训中发挥核心作用：所有学生都将定期使用。

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.