Coherent Manipulation of Second-Harmonic Generation via Terahertz-Field Mediated Phonon-Polariton in Zinc Oxide

The coherent control of phonon polaritons (PhPs) in holds transformative potential for nonlinear photonics. We demonstrate terahertz-driven excitation of low-frequency PhPs in zinc oxide (ZnO) crystals, with their nonlinear dynamics resolved via time-resolved second harmonic generation (SHG) spectroscopy. By achieving phase matching via nine sequential reflections within a millimeter-scale crystal, we observe sustained SHG oscillations with 3–4 THz modulation frequencies, achieving optimal extinction ratios of ~18 dB that persist for 90 picoseconds—a temporal span directly governed by polariton propagation dynamics. This work establishes a dual-functionality platform enabling spectral-temporal resolved mapping of quasiparticle interaction dynamics while simultaneously advancing polariton-engineered nonlinear optical modulators through symmetry-broken frequency conversion architectures.