Excitation of tunable terahertz radiation from a mixture of nanoparticles in static magnetic field

Abstract

This communication deals with the analytical study of terahertz (THz) generation via beat-wave mechanism of two circularly symmetric Gaussian laser beams with frequencies \({\omega }_{1}\) and \({\omega }_{2}\) and wave vectors \({\overrightarrow{k}}_{1}\) and \({\overrightarrow{k}}_{2}\)simultaneously propagating through a mixture of spatially corrugated noble-metal nanoparticles (NPs). The mixture, consisting of spherical and cylindrical nanoparticles, is placed in argon gas under the influence of a static magnetic field. The two co-propagating laser beams impart a nonlinear ponderomotive force on electrons of the NPs, causing them to experience nonlinear oscillatory velocity. Further, the consequent nonlinear current density excites terahertz radiation at the beat frequency \(\omega (={\omega }_{1}-{\omega }_{2})\). Magnetic field influences 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 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. Cylindrical nanoparticles provide greater THz amplitude than spherical nanoparticles due to additional resonance modes, and combining both kinds of nanostructures further enhance the amplitude. THz radiations play an important role in biomedical and pharmaceutical fields, communications, security and THz spectroscopy.