Nonlinear TeraHertz Coherent Excitation of Vibrational Modes of Liquids

TL;DR

This paper demonstrates the first coherent nonlinear excitation of vibrational modes in liquids using terahertz pulses, enhancing spectroscopic capabilities for studying molecular dynamics in condensed phases.

Contribution

It introduces a novel terahertz Kerr effect spectrometer with broader coverage and higher sensitivity, enabling observation of intramolecular vibrational coherences in liquids.

Findings

Vibrational coherences observed at 3.66 THz and 6.50 THz in liquids.

Spectroscopic results match literature values.

Enhanced terahertz spectroscopic techniques developed.

Abstract

We report the first coherent excitation of intramolecular vibrational modes via the nonlinear interaction of a TeraHertz (THz) light field with molecular liquids. A terahertz-terahertz-Raman pulse sequence prepares the coherences with a broadband, high-energy, (sub)picosecond terahertz pulse, that are then measured in a terahertz Kerr effect spectrometer via phase-sensitive, heterodyne detection with an optical pulse. The spectrometer reported here has broader terahertz frequency coverage, and an increased sensitivity relative to previously reported terahertz Kerr effect experiments. Vibrational coherences are observed in liquid diiodomethane at 3.66 THz (122 cm$^{-1}$), and in carbon tetrachloride at 6.50 THz (217 cm$^{-1}$), in exact agreement with literature values of those intramolecular modes. This work opens the door to 2D spectroscopies, nonlinear in terahertz field, that can study the dynamics of condensed-phase molecular systems, as well as coherent control at terahertz frequencies.