Enhanced terahertz emission from the wakefield of CO_{2}-laser-created plasma.

High-field terahertz (THz) pulse generation is investigated through the interaction of an intense single-color CO_{2} laser pulse with helium (He) gas targets. Employing particle-in-cell (PIC) simulations, this study reveals a substantial enhancement in THz generation efficiency, even with a single-color laser pulse interacting with gas targets in the self-modulated-laser-wakefield (SMLWF) regime. Our study demonstrates that in the presence of photoionization, a synergistic interplay of laser self-modulation, self-focusing, and local pump depletion leads to the generation of robust THz pulses polarized parallel to the laser electric field. The dependence of THz generation efficiency on target density, laser intensity, and laser pulse duration has been investigated. Our study identifies a favorable parametric regime for producing THz fields with amplitudes reaching hundreds of GV/m, surpassing those reported in previous studies.