Ultrabroadband Terahertz Coherent Detection with Organic Polymeric Materials

Both solid and gaseous media serve as common platforms for coherent terahertz (THz) detection, yet each faces inherent limitations: solid-state methods such as electro-optic sampling and photoconductive antennas exhibit restricted bandwidth, whereas gas-phase detection typically requires high probe-pulse energies. Here, we demonstrate a coherent THz detection scheme based on a new class of organic polymeric materials. Using low-density polyethylene (LDPE) as a representative example, we combine a THz-induced second harmonic (TISH) signal generated in a laser-induced plasma with a controlled second harmonic (CSH) reference, enabling retrieval of full THz time-domain waveforms spanning 0.1–30 THz. Energy- and polarization-dependent measurements reveal that the TISH signal originates from a four-wave mixing process, opening routes to polarization-sensitive detection and systematic optimization. Relative to air-based detection, the polymeric scheme exemplified by LDPE reduces the required probe energy by an order of magnitude while improving detection sensitivity tenfold. Moreover, the proposed ultrabroadband THz detection scheme offers a substantially broader bandwidth than conventional solid-state techniques, including photoconductive antennas and electro-optic sampling. Importantly, this polymeric approach mitigates signal distortion caused by material phonon absorption and avoids reliance on intricate micro- or nanostructured devices. This work not only establishes a new material paradigm for coherent THz detection but also provides a scalable and tunable foundation, offering promising directions for facilitating its integration into next-generation, high-performance THz sensing and imaging systems.