Fractal spiral zone plate with high-order harmonics suppression

We extend the concept of fractal spiral zone plates and define a new family of Cantor sequence spiral zone plates (CSSZPs) by removing the interference of high-order harmonics. In this typical design, apart from combining the spiral zone plates and Cantor fractal structure together, the desired physical properties have been realized by using a two-parameter modified sinusoidal apodization window along the azimuthal direction to eliminate the high-order harmonics. Numerical simulation reveals that the intensity of high diffraction orders of the CSSZPs can be effectively suppressed by at least 3 orders of magnitude, while the shapes of the sequences of focused optical vortices surrounding the first primary focal length are maintained, similar to those of the fractal spiral zone plates. The demonstration experiment, based on a spatial light modulator, has been also carried out to confirm the desired characteristics. This new kind of diffractive elements may offer potential alternatives for 3D optical tweezers, optical imaging, and lithography.