"Coherent Surface Plasmon Polariton Amplification via Free Electron Pumping" (2022) Ye Tian, Dongdong Zhang, Yushan Zeng, Yafeng Bai, Zhongpeng Li, and 1 more https://doi.org/10.21203/rs.3.rs-1572967/v1

> Abstract: Surface plasmonic with its unique confinement of light is expected to be a cornerstone for future compact radiation sources and integrated photonics devices. The energy transfer between light and matter is a defining aspect that underlies recent studies on optical surface-wave-mediated spontaneous emissions. But coherent stimulated emission, being omnipresent in every laser system, remains to be realized and revealed in the optical near fields unambiguously and dynamically. Here, we present the coherent amplification of Terahertz surface plasmon polaritons via free electron stimulated emission. We demonstrate the evolutionary amplification process with a frequency redshift and lasts over 1-mm interaction length. The complementary theoretical analysis predicts a 100-order surface wave growth when a properly phase-matched electron bunch is used, which lays the ground for a stimulated surface wave light source and may facilitate capable means for matter manipulation, especially in the Terahertz band.

Polariton: https://en.wikipedia.org/wiki/Polariton

Surface plasmon polaritons : https://en.wikipedia.org/wiki/Surface_plasmon_polaritons :

> [...] Application of SPPs enables subwavelength optics in microscopy and photolithography beyond the diffraction limit. It also enables the first steady-state micro-mechanical measurement of a fundamental property of light itself: the momentum of a photon in a dielectric medium. Other applications are photonic data storage, light generation, and bio-photonics.[2][3][4][5]