Ultrafast dynamics of coherent phonons and phonon-polaritons in lithium niobate crystals

Abstract

Abstract This study investigates the ultrafast dynamics of coherent phonons and phonon-polaritons in lithium niobate (LiNbO3) crystals using reflective pump–probe spectroscopy with 25 fs time resolution. In addition to several coherent optical phonon modes, the electro-optic (EO) sampling measurements explored the coexistence of phonon-polariton E-modes near 3.8 and 14.9 THz, which agrees considerably with the theoretical phonon-polariton dispersion curves. We also discovered that a time lag ( Δ t ≈ 0.2 ps) between the coherent optical phonon and phonon-polariton originates from the coupling time for propagating phonon-polariton. Our findings provide a possible application of LiNbO3 for ultrafast EO phonon modulators with bandwidths greater than 10 THz.