Mapping LiNbO_{3} Phonon-Polariton Nonlinearities with 2D THz-THz-Raman Spectroscopy

Area of Science:

• Condensed matter physics
• Nonlinear spectroscopy
• Materials science

Background:

• Understanding phonon mode anharmonicities is crucial for controlling material properties.
• Terahertz-terahertz-Raman spectroscopy offers a pathway to probe these anharmonicities.

Purpose of the Study:

• To investigate the anharmonicities of low-energy phonon modes in lithium niobate (LiNbO3).
• To explore nonlinear transitions between specific phonon polaritons using THz-THz-Raman spectroscopy.

Main Methods:

• Utilizing two-dimensional terahertz-terahertz-Raman spectroscopy.
• Performing measurements on lithium niobate (LiNbO3) crystals.
• Analyzing distinct coherence pathways resulting from different THz polarizations.

Main Results:

• Observed nonlinear transitions between E(TO1) and E(TO3) phonon polaritons.
• Identified distinct coherence pathways dependent on THz polarization.
• Attributed the third-order nonlinear responses to mechanical anharmonicities, not electronic ones.
• Confirmed resonant one-photon THz excitation for E(TO1) and E(TO3) phonon polaritons.

Conclusions:

• The study elucidates the origin of nonlinear responses in LiNbO3, attributing them to mechanical anharmonicities.
• Two-dimensional terahertz-terahertz-Raman spectroscopy effectively probes phonon polariton dynamics.
• Findings provide a foundation for developing strategies for coherent control of material properties.