Femtosecond laser with frequency conversion, pulse shaping, and detection at 100 kHz repetition rate

• Subject Area: Physical Chemistry
• Term: Funded in 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 447563061

We request a new femtosecond laser at 100 kHz repetition rate that will allow us to develop and apply various rapid-scan transient absorption, two-dimensional (2D) spectroscopy, and 2D microscopy techniques with fast data acquisition, improving speed by a factor of up to 100 and allowing new measurement modalities. In particular, we plan to realize shot-to-shot modulation and detection at 100 kHz repetition rate for transient absorption, third-order and fifth-order exciton–exciton-interaction 2D spectroscopy in pump–probe geometry, 2D spectroelectrochemistry, multidimensional multiquantum fluorescence spectroscopy, 2D fluorescence microscopy, ultrafast single-molecule spectroscopy, and quantum control landscape analysis. We propose the 100 kHz repetition rate for all components of the total system, i.e., the laser, frequency conversion via noncollinear optical parametric amplification, a femtosecond pulse shaper, a single-pixel fluorescence detector, a spectrometer-and-camera system for transient absorption detection of probe pulses, and the data acquisition system. Employing rapid-scan methods through 100-kHz shot-to-shot pulse shaping and the associated speed-up in measurement time will facilitate the investigation of kinetically unstable chemical species, additional averaging for improved signal-to-noise ratio, scanning of additional parameters for 3D, 4D, and 5D spectroscopy, accessing higher orders (fourth to tenth) of the response function, micro-spectroscopy of heterogeneous material systems with 300 nm spatial resolution, and other measurement concepts. It is estimated that up to one billion distinct nonlinear signals (i.e., pulse-train time-delay and phase combinations) can be obtained in three hours of data acquisition. Evaluation of the massive data volume is being developed via artificial intelligence approaches (a combination of neural networks and genetic algorithms). Scientific topics to be addressed include the resolution of exciton transport in functional organic materials, exciton annihilation, systematic comparison of exciton diffusion in 1D, 2D, and 3D materials, dynamic processes and charge transfer in biradicals, exciton–phonon coupling in 2D materials, and the investigation of strong coupling in photonic hybrid structures. Currently, the group has no laser system available with the required technical parameters. The proposed device shall form the core of a new laboratory in the “Center for Nanosystems Chemistry” (CNC) at the University of Würzburg. A dedicated microscopy cryostat for ultrafast, spatially resolved 2D experiments will be financed by separate funds to reduce the overall cost of the current proposal.

• DFG Programme: Major Research Instrumentation
• Major Instrumentation: Femtosekundenlaser mit Frequenzkonversion, Pulsformung und Detektion bei 100 kHz Repetitionsrate
• Instrumentation Group: 5700 Festkörper-Laser
• Applicant Institution: Julius-Maximilians-Universität Würzburg
• Leader: Professor Dr. Tobias Brixner