Zone plate designs for terahertz frequencies (Invited Paper)

TLDR: The phase-correcting Fresnel zone plate provides lens-like focusing and imaging of electromagnetic waves by means of diffraction instead of refraction, often referred to as diffraction optics.

Abstract: The phase-correcting Fresnel zone plate provides lens-like focusing and imaging of electromagnetic waves by means of diffraction instead of refraction, often referred to as diffraction optics The zone plate has seen extensive investigation and use at microwave and millimeter-wave frequencies, and recently has been applied in the terahertz region These cases have dealt principally with large-angle designs, where the focal length (F) and diameter (D) are comparable (F/D = 03 to 25), unlike the typical optical examples The planar zone plate, in particular, offers the advantages of simplicity of design and construction, low loss, low weight, and low cost, while giving performance similar to that of a refractive lens As one goes to terahertz frequencies, ease of construction becomes more difficult The attenuation in conventional low-loss materials increases at higher frequencies, and dimensional tolerances become smaller, making fabrication more difficult Although earlier designs employing polystyrene have been built and tested at frequencies up to 280 GHz, higher frequency designs are simpler to fabricate and have lower loss if low dielectric constant materials are used This investigation addressed designs for terahertz frequencies The optimization of the zone plate has also been examined, and improvement has been found for radial compression, where the radii of the zone boundaries are slightly shortened