Magnetic field enhanced terahertz generation from shape-dependent metallic nanoparticles

This communication deals with the analytical study of terahertz (THz) generation via frequency-difference mechanism using two circularly symmetric Gaussian laser beams with slightly different frequencies omega 1 and omega 2 and wave vectors k -> 1 and k -> 2 simultaneously propagating through a mixture of spatially corrugated noble-metal nanoparticles. The mixture, consisting of spherical nanoparticles (SNPs) and cylindrical nanoparticles (CNPs), is placed in a host medium under the influence of an externally applied static magnetic field. The two co-propagating laser beams impart a nonlinear ponderomotive force on the electrons of the NPs, causing them to experience nonlinear oscillatory velocity. Furthermore, the consequent nonlinear current density excites THz radiation at the beat frequency omega (=omega 1-omega 2). Magnetic fields influence the surface plasmon resonance condition associated with electrons of the nanoparticles due to enhancement in ponderomotive nonlinearities, thereby causing an increment in the amplitude of the generated THz field. It is observed that the generated THz radiation has a strong dependence on the shape and size of the NPs in addition to the magnetic field strength. CNPSs provide greater THz amplitude than SNPs due to additional resonance modes, and combining both kinds of nanostructures further enhances the amplitude. THz radiation plays an important role in biomedical and pharmaceutical fields, communications, security and THz spectroscopy.