Phase quasi-random squares spiral zone plates with single-focus diffraction.

Due to the existence of orbital angular momentum, an optical vortex generated from spiral zone plates is an important approach for studying physics and detecting matter. However, the unneeded high-order diffraction inherent in traditional spiral zone plates will add background noise, leading to complication in subsequent analysis. In this paper, a single-focus spiral zone plate with an approximately sinusoidal transmittance, called phase quasi-random squares spiral zone plates (PQRSZPs), is designed. The key idea of the PQRSZPs is to transform the three-dimensional sinusoidal structure of the sinusoidal spiral zone plates into a three-dimensional square structure with a phase difference of 2, making it easy to fabricate. Theoretical analysis and experimental results confirm that the PQRSZPs can effectively remove high-order diffraction and increase the diffraction intensity of the wanted order. Moreover, the helical phase structure with multiple topological charges of the output beams is also demonstrated. Due to this unique property, there are widespread applications in astrophysics and imaging.