Nonlinear mixing-based terahertz emission in inclined rippled density plasmas

Abstract

We propose to investigate the THz field generation using nonlinear mixing mechanism of laser beat wave with inclined rippled density plasmas. Two laser pulses with frequencies (ω 1, ω 2) and wave vectors (k 1, k 2) co-propagate and resultant laser beat wave forms at beat frequency (ω 1–ω 2). Laser beat wave imparts a nonlinear force on the ambient electrons and pushes them outward with nonlinear velocity v NL. Coupling of induced density perturbation and nonlinear velocity v NL generates nonlinear currents at laser beat frequency that further generates electromagnetic field E (ω 1–ω 2) in terahertz (THz) range. In the present scheme, density ripples are introduced at an angle with respect to laser propagation and flat Gaussian index (f) is introduced in laser field profile that transform curved top of Gaussian field envelope into flat top field envelope. The combined effect of flat laser pulses with inclined density ripples in plasmas shows 10-fold enhancement in THz field amplitude when flat-Gaussian index (f) varies from 1 to 4. Also, the THz field intensifies when density ripples inclination increases upto a certain angle and then decreases.