Generation of high-quality terahertz OAM mode based on soft-aperture difference frequency generation

We demonstrate the generation of high-quality tunable terahertz (THz) vortices in an eigenmode by employing soft-aperture difference frequency generation of vortex and Gaussian modes. The generated THz vortex output exhibits a high-quality orbital angular momentum (OAM) mode with a topological charge of ℓ_THz = ±1 in a frequency range of 2-6 THz. The maximum average power of the THz vortex output obtained was ∼3.3 µW at 4 THz.