Gradient index devices for terahertz waves and terahertz surface waves

We demonstrate a variety of gradient index (GRIN) devices for both freely propagating terahertz waves and terahertz surface waves. As a specific example of a static GRIN optics we experimentally investigated and measured the optical properties of a GRIN beam deflector. We measured a maximum deflection angle of 6 deg. The thickness of the beam deflector was only about 100 mu m which is sub-wavelength at a frequency of 1.3 THz. Furthermore, we specifically designed meta-surfaces that support strongly confined terahertz surface waves. We show that the surface waves can be deliberately guided within the plane of propagation by use of GRIN structures. For example, we evidenced the focusing behavior of a meta-surface GRIN lens by near-field mapping of the terahertz field.