title: Nonlinear two-dimensional terahertz photon echo and rotational spectroscopy in the gas phase.
abstract: Ultrafast 2D spectroscopy uses correlated multiple light-matter interactions for retrieving dynamic features that may otherwise be hidden under the linear spectrum; its extension to the terahertz regime of the electromagnetic spectrum, where a rich variety of material degrees of freedom reside, remains an experimental challenge. We report a demonstration of ultrafast 2D terahertz spectroscopy of gas-phase molecular rotors at room temperature. Using time-delayed terahertz pulse pairs, we observe photon echoes and other nonlinear signals resulting from molecular dipole orientation induced by multiple terahertz field-dipole interactions. The nonlinear time domain orientation signals are mapped into the frequency domain in 2D rotational spectra that reveal J-state-resolved nonlinear rotational dynamics. The approach enables direct observation of correlated rotational transitions and may reveal rotational coupling and relaxation pathways in the ground electronic and vibrational state.
authors.affiliation: Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139.
authors.forename: Jian
authors.initials: J
authors.lastname: Lu
authors.affiliation: Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139.
authors.forename: Yaqing
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139.
authors.forename: Harold Y
authors.initials: HY
authors.lastname: Hwang
authors.affiliation: Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139.
authors.forename: Benjamin K
authors.initials: BK
authors.lastname: Ofori-Okai
authors.affiliation: Department of Chemical Physics, Tel-Aviv University, Tel Aviv 69978, Israel.
authors.forename: Sharly
authors.initials: S
authors.lastname: Fleischer
authors.affiliation: Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139; kanelson@mit.edu.
authors.forename: Keith A
authors.initials: KA
authors.lastname: Nelson
keywords: multidimensional coherent spectroscopy; rotational dynamics; terahertz; ultrafast spectroscopy