Enhanced terahertz phonon polariton in lithium niobate wafer

Abstract Terahertz (THz) phonon polariton, a fundamental quasi-particle that couples phonon and electromagnetic fields in THz frequencies, is present in diverse materials, imparting multifarious functionalities to comprehend THz electromagnetic wave-matter interactions while enabling diverse THz optoelectronic devices and integrated systems. Despite the potential of THz phonon polariton, its proliferation is hampered by the absence of strong-field THz sources and highly sensitive electromagnetic spectra detection tools in the THz region. In this study, we showcase the efficient generation and amplification of THz phonon polaritons in lithium niobate wafers via optical-to-THz phase matching employing tilted pulsefront technique. The THz phonon polariton is imaged using spatiotemporal phase contrast imaging, with lateral pumping and phase matching allowing for the extension of the effective interaction length in lithium niobate wafers exceeding several millimeters. The observed THz phonon polariton in lithium niobate using tilted pulsefront phase matching unlocks new nonlinear THz optics possibilities. We envision that it may lead to potential applications in on-chip THz photonic devices and systems based on lithium niobate materials and its integrated heterostructures.