Setup for nonlinear multi-terahertz spectroscopy

• Subject Area: Condensed Matter Physics
• Term: Funded in 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 497211903

The goal of this proposal is to build an experimental setup to conduct nonlinear multi-terahertz spectroscopy of condensed matter. Central feature are intense femtosecond laser pulses with tunable center frequency from the far-infrared to the visible spectral range. The focus is on electromagnetic pulses in the multi-terahertz (THz) range with center frequencies from 1 to 50 THz and field strengths of 10 MV/cm and 3 T and beyond. By applying such pulses to solids, we will selectively trigger and interrogate the dynamics of electrons, their spins and the crystal lattice. The goal of this pump-probe approach is to reveal and understand the coupling mechanisms between the various degrees of freedom. An important example is the interaction between magnetic order and the crystal lattice (i.e. phonons). Using the same approach, we will also investigate solvents to gain new insights into the collective motions of the molecules and their couplings. Potential applications of these experiments are the selective writing and transport of magnetic information in solids and the preparation of new solvent states, which may enable more efficient chemical reactions. To build such a setup, (i) sources of intense laser pulses in the visible, infrared and THz frequency range, (ii) components to characterize the pulses and steer them to the experiment as well as (iii) components for the low-noise detection and computer-based acquisition of the signals are necessary. Point (i) requires an amplified titanium:sapphire laser system (pulse energy ~7 mJ, pulse duration 35 fs, pulse repetition rate 1 kHz, center wavelength 800 nm) with two subsequent infrared-optical parametric amplifiers (wavelength range 1.16-1.6 µm and 1.6-2.6 µm for signal and idler, respectively, and conversion efficiency 25% for signal+idler) and two frequency mixers (sum and difference frequency) as well as suitable nonlinear-optical crystals and optical and opto-mechanic components (such as mirrors, lenses, polarization optics and translation/rotation stages). For (ii), power meters, spectrometers, an autocorrelator and cameras are needed, while (iii) requires components such as photodetectors, oscilloscopes, electrical amplifiers and hardware for computer-based data acquisition. The proposed setup is essential for the implementation of running, submitted and planned third-party-funded projects. Because the applicant’s research group has significant experience with multi-THz pump-probe experiments, a time-efficient building of the setup is expected.

• DFG Programme: Major Research Instrumentation
• Major Instrumentation: Messplatz für nichtlineare Multi-Terahertz-Spektroskopie
• Instrumentation Group: 5700 Festkörper-Laser
• Applicant Institution: Freie Universität Berlin
• Leader: Professor Dr. Tobias Kampfrath