Laser interaction and terahertz radiation generation in a longitudinally inhomogeneous plasma

Abstract This study demonstrates an analytic framework for generating terahertz (THz) radiation through the nonlinear interaction of frequency-varying lasers with a longitudinally nonuniform plasma. When two lasers beat the plasma density gradient at an angle, it imparts an oscillatory velocity to the plasma electrons. Variation in laser amplitude creates a non-linear ponderomotive force that oscillates at the beating frequency of the laser, typically within the THz range. This force drives a non-linear current density in the plasma, with its transverse component contributing to the generation of THz radiation. Using a frequency-varying laser prolongs the interaction time between the laser and the plasma, leading to the production of broadband THz radiation. Optimizing key factors, such as the angle of the laser relative to the plasma, its time-dependent frequency, and its intensity, allows the control of the THz radiation power. These optimized conditions are essential for developing efficient THz sources for various practical applications.