Terahertz circular Airy vortex beams.

Vortex beams have received considerable research interests both in optical and millimeter-wave domain since its potential to be utilized in the wireless communications and novel imaging systems. Many well-known optical beams have been demonstrated to carry orbital angular momentum (OAM), such as Laguerre-Gaussian beams and high-order Bessel beams. Recently, the radially symmetric Airy beams that exhibit an abruptly autofocusing feature are also demonstrated to be capable of carrying OAM in the optical domain. However, due to the lack of efficient devices to manipulate terahertz (THz) beams, it could be a challenge to demonstrate the radially symmetric Airy beams in the THz domain. Here we demonstrate the THz circular Airy vortex beams (CAVBs) with a 0.3-THz continuous wave through 3D printing technology. Assisted by the rapidly 3D-printed phase plates, individual OAM states with topological charge l ranging from l = 0 to l = 3 and a multiplexed OAM state are successfully imposed into the radially symmetric Airy beams. We both numerically and experimentally investigate the propagation dynamics of the generated THz CAVBs, and the simulations agree well with the observations.