High-power terahertz non-diffractive bessel beams with angular orbital momentum: Generation and application

Using radiation of the Novosibirsk free electron laser (NovoFEL) and silicon binary phase plates with spiral Fresnel zone patterns, we generated for the first time non-diffracting terahertz Bessel beams with angular orbital momentum (“vortex beams”) and topological charges l = ±1,±2. The amplitude and phase characteristics of the beams at a wavelength of 141 μm were thoroughly investigated and showed excellent agreement with numerical modelling based on scalar diffraction theory. We have demonstrated self-reconstruction of the beams passing non-uniform media. We studied the peculiarity of vortex beam diffraction on different apertures, generated surface plasmon polaritons by the end-fire coupling technique, and discovered unusual features in the mechanism of coupling of the vortex beams.