Nonlinear two-dimensional terahertz photon echo and rotational spectroscopy in the gas phase

Jian Lu, Yaqing Zhang, Harold Y. Hwang, Benjamin K. Ofori-Okai, Sharly Fleischer, Keith A. Nelson

Research output: Contribution to journalArticlepeer-review


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.

Original languageEnglish
Pages (from-to)11800-11805
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number42
StatePublished - 18 Oct 2016


  • Multidimensional coherent spectroscopy
  • Rotational dynamics
  • Terahertz
  • Ultrafast spectroscopy


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