Summenfrequenz-Spektrometer

• Subject Area: Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: Funded in 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 549581038

The application is for a "SFG Spectroscopy for Plasma Surface Interaction" measuring station consisting of a tunable infrared laser and a visible laser, the corresponding optics, a measuring cell and measuring electronics. This measuring station will play a central role in the recently appointed "Plasma Interface Physics" working group at Ruhr-Universität Bochum. The main aim is to measure solid and liquid interfaces of surfaces in contact with plasmas. Sum Frequency Generation (SFG) spectroscopy is sensitive to molecules absorbed on the surface that are active in the infrared. These molecules are crucial for the majority of beneficial applications caused by non-equilibrium plasmas, such as etching and coating as well as the new research field of plasma catalysis and biomedical applications. Measurands: Sum frequency generation Vibrational spectroscopy (SFG-VS) is a powerful and versatile method for the in-situ investigation of surfaces and interfaces. In the SFG-VS experiment, a pulsed, tunable infrared (IR) laser beam is mixed with a visible (VIS) beam at a surface to obtain a tunable output beam with the sum frequency. SFG is a second-order non-linear process that only occurs in media without inversion symmetry. At surfaces or interfaces, the inversion symmetry is necessarily broken, which makes SFG extremely surface-sensitive. This means that monolayers can be analyzed on surfaces. When the IR wavelength is scanned, active vibrational modes of the molecules at the interface are excited and give a resonant contribution to the SF signal. The resonance amplification provides spectral information about characteristic surface vibrational transitions. Components: The components for the SFG spectrometer include a tunable IR laser and a visible laser, corresponding optics for focussing, deflection and mixing as well as corresponding detectors and evaluation electronics to generate the spectra. Projects: The majority of the working group's projects will benefit from the measuring station. In one important project, the effect of plasma in contact with conventional catalysts is to be determined as operando as possible. A second project is focussed on the interaction of reactive water plasmas with aqueous solutions for biocatalysis. Other projects in preparation are concerned with the etching properties of reactive fluorine-containing gases on glass surfaces. In addition, the entire SFB is concerned with the interaction of plasmas with surfaces or at interfaces, so that an SFG spectrometer will make a valuable contribution to many sub-projects here.

• DFG Programme: Major Research Instrumentation
• Major Instrumentation: Sum Frequency Generation Spektrometer
• Instrumentation Group: 5700 Festkörper-Laser
• Applicant Institution: Ruhr-Universität Bochum
• Leader: Professorin Dr. Judith Golda