Broadband terahertz wave generation from an epsilon-near-zero material

Abstract

Terahertz radiation: thin film enhancement A new method for generating terahertz waves exploits the low-permittivity properties of an ultrathin film. Terahertz radiation, falling between the infrared and microwave range, has emerging applications in imaging, communications and materials inspection, and is usually generated through the rectification of optical signals in nonlinear crystals. Yuanmu Yang at Tsinghua University in Beijing and co-workers tried an alternative approach, directing a near-infrared laser onto commercially available films of indium tin oxide just 19 nanometres thick. They observed a large enhancement in the terahertz generation when they tuned the laser to hit the film’s ‘epsilon-near-zero’ state—a point where the permittivity of the thin film becomes vanishingly small. The method is relatively inefficient, but the researchers suggest that it could be enhanced by using other thin films in conjunction with metamaterials.