Sunday, April 4, 2021

Abstract-Two-dimensional terahertz spectroscopy of condensed-phase molecular systems

 

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Klaus Reimann,  Michael Woerner. Thomas Elsaesser, 

Setup for three-pulse measurements. BS are beam splitters, Q are quartz glass windows for the vacuum chamber, NL are nonlinear crystals for THz generation (GaSe), ZnTe is the electro-optic crystal, λ/4 is a quarter-wave plate, WP is a Wollaston polarizer, and PD1 and PD2 are silicon photodiodes. The detected signal is the difference of the outputs of PD1 and PD2.

https://aip.scitation.org/doi/full/10.1063/5.0046664

Nonlinear terahertz (THz) spectroscopy relies on the interaction of matter with few-cycle THz pulses of electric field amplitudes up to megavolts/centimeter (MV/cm). In condensed-phase molecular systems, both resonant interactions with elementary excitations at low frequencies such as intra- and intermolecular vibrations and nonresonant field-driven processes are relevant. Two-dimensional THz (2D-THz) spectroscopy is a key method for following nonequilibrium processes and dynamics of excitations to decipher the underlying interactions and molecular couplings. This article addresses the state of the art in 2D-THz spectroscopy by discussing the main concepts and illustrating them with recent results. The latter include the response of vibrational excitations in molecular crystals up to the nonperturbative regime of light–matter interaction and field-driven ionization processes and electron transport in liquid water.

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