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DS: Fachverband Dünne Schichten

DS 20: Poster

DS 20.37: Poster

Donnerstag, 12. März 2026, 18:30–20:30, P2

Heterodyne detection of the second harmonic signal in THz pump - optical probe experiments — •Sergei Ovcharenko, Alexey Melnikov, and Georg Woltersdorf — Institut für Physik, Martin-Luther-Universität Halle, 06120 Halle (Saale), Germany

Broadband Terahertz (THz) radiation is a widely used for resonant excitation of magnon modes or spin waves in magnetic materials. Furthermore, studying the THz emission from ferromagnetic (FM) materials allows us to investigate elementary processes in ultrafast spintronic. However, experimental investigation of such effects requires broadband THz detection: the commonly used sampling in electro-optical crystals is limited by phonon absorption, Zeeman-torque sampling requires accurate determination of the magneto-optical constants of a specific FM sample. An alternative approach is the detection of the THz field-induced second harmonic (TFISH) signal, based on third-order nonlinearity χ(3) in ambient air gases. Heterodyne detection, interference between the TFISH and SH light from a reference source, allows retrieval of the full THz pulse profile. The SH heterodyning technique is also applicable to extract weak SH signals, related to THz-induced magnetization dynamics in thin films. Our work reveals a phase modulation effect in the heterodyne TFISH signal: the air gap between TFISH and reference SH sources alters the detected THz pulse shape and spectrum through propagation effect in presence of the THz field. Using the developed instrument, we performed test experiments on heterodyne SH detection of THz-induced magnetization dynamics.

Keywords: THz; Pump-probe; SHG; SH heterodyne detection; TFISH