Quasi-single-order focusing zone plate with trapezoidal transmittance

We designed a novel zone plate by employing the trapezoidal transmission function. Numerical simulations based on Fresnel-Kirchhoff diffraction theory have demonstrated the quasi-single-order focusing characteristic and different performance of this plate from Fresnel zone plate. The comparison with a binary Gabor zone plate shows that the first-order diffraction efficiency of this plate is about 11.3% higher. Besides, all foci with orders of 2q and 3q(q=1,2,3,) are eliminated for this plate, and the diffraction efficiency of the fifth order is only 1/625 of the first order theoretically. More importantly, due to its symmetric structure and duplicable sectors that have equal width in a half-wave zone, this plate is much easier for nanofabrication.