Second-order Harmonic Generation in CNT arrays for THz Wave Emission

Two laser beams with frequencies ω₁ and ω₂, wave vectors k₁ and k₂ are transmitted through a network of CNTs placed on a dielectric substrate. When these laser pulses come into contact with nanotubes, a confined plasma is created. Electrons acquire oscillatory velocities as a result. The electrons experience ponderomotive pressure, which results in oscillations in the charge density at 2ω₁ and ω₁-ω₂. The laser applies a ponderomotive force to the free electrons in carbon nanotubes at the frequency 2ω₁-ω₂, which is in the terahertz (THz) zone, resulting in a nonlinear current density. Every nanotube emits THz radiation by acting as an oscillating electric dipole. We determine the THz efficiency controlling formula and its reliance on the CNT spacing, size, amplitude, and angle of laser incidence. At the incident angle θ ≈ 23.5^o, we acquire the greatest peak of THz power. Carbon nanotube terahertz power is directly proportional to their length and radius, meaning that an increase in any of these two factors will result in an increase in terahertz power. THz efficiency rises as the distance between the nanotubes decreases.