Direct Observation and Ultrafast Optical Manipulation of Intermode Exciton‐Polariton Parametric Scattering Lasing

ABSTRACT The hybrid light‐matter character of exciton‐polaritons gives rise to distinct polariton parametric scattering (PPS) processes, which hold promise for frontier applications in polaritonic quantum devices. However, the stable excitation and coherent optical manipulation of PPS remain challenging due to scattering bottlenecks and rapid dephasing in polariton many‐body systems. In this study, we first report the direct observation and optical amplification of non‐degenerate intermode PPS lasing at room temperature (RT). The specific polariton branch of strong‐coupled nanobelt planar microcavity is resonantly excited by a near‐infrared (NIR) femtosecond laser via two‐photon absorption (TPA) scheme, and the non‐degenerate signal‐ and idler‐states are stimulated. Angle‐resolved dispersion patterns clearly reveal the evolution of the pump‐, signal‐, and idler‐states under different excitation powers. Based on our self‐constructed ultrafast femtosecond resonant optical trigger setup, a selective enhancement and modulation of the signal‐state is realized. Furthermore, the dynamic measurements of nonlinear signal‐state enhancement process demonstrate a sub‐picosecond response time (0.4 ps), confirming its potential for ultrafast optical manipulation. Our work establishes a platform for exploring TPA‐driven PPS laser and provides a novel optical modulation route for polariton‐based optoelectronic devices.