Laser- and Detectionsystem for transient absorption spectroscopy with two excitation pulses

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The proposed spectrally tunable femtosecond laser system and detection system for time-resolved transient absorption spectroscopy with the optional use of a second excitation pulse will enable the time-resolved characterization with fs time resolution of ultrafast light-driven processes in photoactive systems. The proposed device will strengthen the strategic research field of the RPTU Kaiserslautern-Landau for investigating the interaction of light, spin and matter, specifically addressed in the profile area of the Research Initiative of the Federal State of Rhineland-Palatinate within the Center for Optics and Materials Sciences (OPTIMAS). One focus of the planned projects in the applicants working groups in the Department of Chemistry, in which the proposed device will be used, is the investigation of light-induced processes in materials for light-driven redox catalysis, e.g. the generation of hydrogen by reducing water. With the planned laser and detection system, the fundamental light-driven processes in colloidal semiconductor nanostructures, e.g. quantum dots and nanorods, such as exciton relaxation processes, charge carrier localization and recombination, and energy and charge carrier transfer between the components of hybrid materials based on these nanostructures will be investigated. The general goal of the work is to understand the basic mechanisms that lead to a desired function and to use the knowledge gained to improve the systems based on the derived structure-dynamics-function relationships. The option of using multiple excitation pulses will make it possible to study specific processes involving multiple charge carriers from a new perspective. The transfer of several charge carriers requires either a step-by-step consecutive charge transfer through successive excitation/charge transfer sequences or a simultaneous generation of several charge carriers and their quasi-simultaneous transfer to a suitable reaction center. These scenarios are to be investigated in photoactive hybrid materials based on colloidal semiconductor nanostructures with the proposed system. In addition, the laser system will enable the investigation of ultrafast molecular processes such as charge, energy, and spin transfer in functional transition metal compounds in both, the condensed phase by transient absorption spectroscopy and in the gas phase by observing fragmentation dynamics.