Lateral terahertz emission from shaped plasma excited by colliding laser pulses

Plasma-based terahertz (THz) sources are generally limited by a saturation effect and consequent optical-THz conversion efficiency. Extending plasma volume is an effective approach to mitigate the saturation effect and increase THz generation efficiency. By reshaping gas plasma using two pairs of cylindrical lens to focus two counter-propagating laser pulses, we demonstrate enhanced broadband coherent THz radiation through the interaction of colliding laser pulses with gas plasma. The use of the cylindrical lens pairs changes the plasma shape to mitigate the THz saturation and increase the THz generation efficiency. The peak THz amplitude generated by cylindrical lens pairs is more than twice of that by spherical lenses. This method provides an important option for the development of promising terahertz sources.