High-resolution binary zone plate in double-sided configuration for terahertz radiation focusing

A double-sided phase-reversal binary zone plate is numerically investigated and experimentally characterized at the frequency of 1 THz.The double-sided zone plate has a novel design based on a binary phase-reversal zone plate, in which the total zone thickness is split into two halves located at a distance optimized by means of numerical simulations.The samples are fabricated by a three-axis milling technique on slabs of an ultralow-loss cyclo-olefin polymer.The lenses' characterization at the frequency of 1 THz is performed by means of a terahertz time-domain spectrometer, in terms of both focal length and spatial resolution.The focusing properties of the double-sided zone plate are compared with those of a conventional binary zone plate.The double-sided zone plate features $2.4 imes $ smaller focal spot, $1.25 imes $ higher focusing efficiency, and an approximately $10lambda -mathbf 0$ longer depth of field than the conventional binary configuration