Abruptly autofocusing terahertz waves with meta-hologram.

An abruptly autofocusing ring-Airy beam is demonstrated in the terahertz (THz) waveband with a meta-hologram. The designed meta-hologram is composed of gold C-shaped slot antennas, which can realize both phase and amplitude modulation of the incident THz wave. A THz holographic imaging system is utilized to measure the generated ring-Airy beam; an abrupt focus following a parabolic trajectory is subsequently observed. THz ring-Airy beams with different parameters are also generated and investigated. This method can be expanded to other wavebands, such as the visible band, for which the meta-hologram can replace traditional computer-generated holography to avoid undesirable multiple diffraction orders.