Tuneable Femtosecond Laser Sources for Time-Resolved Ultrafast Spectroscopy

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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.