Relativistic Terahertz Laser Pulse from Photon Deceleration in Plasma Wakefield

Abstract Terahertz (THz) radiation, spanning the 100 GHz to 10 THz frequency range, offers diverse applications in spectroscopy, material characterization, medical diagnostics, and environmental monitoring. Despite its potential, generating high-intensity, tunable THz radiation remains a significant challenge. In this work, we explore a novel approach to efficient THz generation based on laser-plasma interactions, utilizing photon deceleration principles. When a relativistic CO 2 laser passes through a pre-ionized plasma, the laser induces a nonlinear wakefield, creating a strong refractive index gradient. This gradient, combined with the lower-density region of the wakefield, slows down the laser, facilitating the accumulation of THz radiation. The resulting THz pulse exhibits extreme collimation, high energy efficiency, and tunability. Our work shows that this method can achieve up to 10% conversion efficiency, with optimal plasma density near the critical density. This technique presents a promising solution for overcoming current limitations in THz source development and offers potential for diverse applications.