Pump-Probe Spectrometer with 3rd Pulse for Transient Absorption and Stimulated Raman Spectroscopy

• Subject Area: Chemical Solid State and Surface Research
• Term: Funded in 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 542544322

The requested device is a transient absorption pump-probe spectrometer for the measurement of ultrafast dynamics on the timescale of 200 fs to 4 ns in the visible range of the spectrum, with an additional, third, narrow-band laser pulse to conduct femtosecond stimulated Raman scattering (FSRS) spectroscopy. The grant application includes a femtosecond pulsed laser, two optical parametric amplifiers (OPA) and second harmonic generators (SHG) for femtosecond and picosecond pulses with variable wavelength, a pump-probe spectrometer with white light generation and delay stage, third laser beam delivery module, and a software solution for data analysis. Transient absorption spectroscopy is a pump-probe method, in which an absorbing sample is excited by an ultrashort laser pulse, followed after a time delay by a white light pulse to obtain an absorption spectrum of the excited state. The difference spectra between the ground and excited state absorption yield valuable information on the electronic structure, while the variable delay between pump and probe pulse gives information on the kinetics of the relaxation process back to the ground state. The spectrometer will form a core competence of the newly established Photonic Nanomaterials group at the University of Rostock, where it will be used extensively to investigate photo-excited charge carrier dynamics in colloidal nanocrystals and nano-heterostructures, particularly across heterointerfaces. The third pulse option will be employed for FSRS, in which the probe pulse is over-lapped with a longer pulse with narrow bandwidth. This causes stimulated Raman scattering of either the ground or an excited state with exceptional time resolution (50-150 fs) and a much better signal-to-noise ratio than for normal Raman spectra. The method will be employed to develop a new method for mapping the position and spatial extent of excited electron/hole pairs (excitons) to the chemical structure of a nano-material. This shall be accomplished by resonantly exciting the particles and exploiting exciton-phonon coupling to correlate the resulting Raman modes with the material in which the exciton resides. Furthermore, FSRS will form the basis for numerous collaborations within the University of Rostock, neighbouring institutes like the Leibnitz Institute for Catalysis, and beyond.

• DFG Programme: Major Research Instrumentation
• Major Instrumentation: Pump-Probe-Spektrometer mit 3. Puls für transiente Absorptions- und stimulierte Raman-Spektroskopie
• Instrumentation Group: 5700 Festkörper-Laser
• Applicant Institution: Universität Rostock
• Leader: Professor Dr. Klaus Boldt