Effect of magnetic field on terahertz emission using amplitude-modulated lasers from shape-dependent metallic nanoparticles

This study presents an analytical investigation of terahertz (THz) radiation generation resulting from the beat-wave interaction of amplitude-modulated Gaussian laser beams with metallic spherical and cylindrical nanoparticles (NPs) under an externally applied static magnetic field. This scheme involves the resonant excitation of THz radiation through the beat-wave of two lasers in the presence of ponderomotive nonlinearities, which drive a nonlinear current density acting as the primary source of THz emission. The analytical model incorporates the spatial and temporal variations of the ponderomotive force arising from the amplitude modulation, thereby enhancing the nonlinear current response. The incorporation of the magnetic field significantly enhances laser–metal coupling and alters the surface plasmon resonance conditions of the NPs’ electrons, leading to much stronger THz emission. The study systematically examines the influence of magnetic field strength, NP radius and interparticle spacing, and modulation index of the incident laser on the THz amplitude. Results indicate that the THz field strength increases with enhanced magnetic field and larger NP radii, while decreased interparticle spacing promotes stronger near-field interactions, further amplifying the emission. The combined use of spherical and cylindrical NPs introduces multiple plasmonic resonance modes, enabling more efficient energy conversion. This work provides important insights into the optimization of NP-based THz sources for applications in spectroscopy, imaging, and wireless communication.