THz generation by non-linear mixing of laser and its second order harmonic on CNT array inlaid over dielectric substrate

Abstract

A network of CNTs embedded on a dielectric substrate is used to transmit two laser beams with frequencies \({\upomega }_{1}\) and \({\upomega }_{2}\) and wave vectors \({\text{k}}_{1}\) and \({\text{k}}_{2}\) respectively. These laser pulses cause a localized plasma to develop when they contact with nanotubes. As a result, electrons develop oscillatory velocities. By applying ponderomotive pressure to the electrons, it causes oscillations in the charge density at \(2{\upomega }_{1}\) and \({\upomega }_{1}-{\upomega }_{2}\) frequencies. At the frequency \(2{\upomega }_{1}-{\upomega }_{2}\), which is in the terahertz (THz) region, the laser exerts a ponderomotive force on the free electrons of carbon nanotubes causing a nonlinear current density. Each nanotube functions as an oscillating electric dipole that emits THz radiation. We establish the governing equation for THz efficiency and its dependence on laser incidence angle, amplitude, nanotube size, and CNT spacing. We obtain maximum peak of THz power at incident angle \({\uptheta }_{0}\approx 23.{5}^{^\circ }\). The terahertz power of carbon nanotubes is highly dependent on their radius and length, so as these parameters increase, their terahertz power increases as well. Whereas on decreasing separation between the nanotubes, THz efficiency increases.

Graphical abstract