An optical vortex carries an annular intensity spatial profile and an orbital angular momentum characterized by a topological charge, ℓ, which allows us to explore various research fields, including optical trapping, optical telecommunication, fabrication of structured materials and super-resolution microscopy. In particular, terahertz (THz) vortex will provide new advanced spectroscopic technologies, such as 2-dimesional identification of the biomaterials with a high spatial resolution beyond the diffraction limit.

The generation of THz vortices was already demonstrated by using several optical devices based on wavefront conversion, such as a molded phase plate composed, and a spiral phase plate (SPP). However, these devices are typically designed for a specific frequency, which inherently constrains the wavelength tunability of the THz vortices.

In this presentation, we report a tunable THz vortices generation with a frequency range of 2-6 THz at a topological charge of ℓTHz = ± 1, based on the 1.5μm optical vortex pumped difference frequency generation (DFG) from a 4ʼ-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST) crystal.