Controlling the angular divergence of terahertz radiation generated by single-color filaments using phase optical elements

We have experimentally obtained two-dimensional distributions of terahertz radiation generated by one or four filaments formed by phase optical elements in air. It has been demonstrated that the use of the phase mask reduces the propagation angles of terahertz beam by approximately one and a half times, which is due to the interference of terahertz radiation from four sources. The use of the Dammann grating slightly enlarges these angles.