<p>This paper presents an analytical model for terahertz (THz) generation that examines the interaction of amplitude-modulated laser beams with graphite nanoparticles in the presence of an external electric field and wiggler magnetic field. Our study focuses on the non-linear current dynamics within the NPs, emphasizing the role of anharmonic electron oscillations and the effects of the external applied fields. The findings reveal that the anharmonic response of NPs electrons, coupled with the external electric and magnetic fields, enhances the non-linearity within the system, leading to significantly amplified THz emission. Additionally, we examine how the modulation index, nanoparticle radius, and inter-particle distance affect THz amplitude. This research provides critical insights into optimizing THz generation mechanisms, paving the way for developing compact and efficient THz sources.</p>