3D printed flat optics and InP heterojunction bipolar transistor based-detector for THz imaging

Diffractive optical elements such as hyperbolic lens and quasi-spherical lens converting a divergent terahertz beam into the focal line segment perpendicular to the optical axis was designed. Due to the fact that the length of the line segment was longer than the aperture of the designed elements the non-paraxial approach was used. The structures were designed for the narrowband application as kinoform elements. The theoretical approach, computer simulations and experimental results are presented. In the imaging system, the intensity of the radiation in the focal plane was measured by THz point-like detector based on InP heterojunction bipolar transistor.