Optimal focusing for single-color laser filamentation to generate terahertz radiation

We study the influence of the laser beam numerical aperture on the energy of different spectral components of terahertz emission from single-color filament plasma. The parameters of the plasma channel, laser pulse after filamentation, and their correlation with the terahertz energy are analyzed. It is demonstrated that by varying the numerical aperture, the terahertz energy can be increased by more than an order of magnitude, and the optimal focusing of the laser beam corresponds to the transition from filamentation regime with nonlinear focusing to the regime with geometric focusing prevalence.