Holographic Generation of Bessel–Gaussian Vortex Beams Using a Ring-Apertured Fork Grating and Topological Charge Measurement via an Astigmatic Grating

In this work, we introduce a holography-based method for generating Bessel–Gaussian vortex beams (BGVBs). The approach embeds a helical phase into a diffraction grating and then applies a ring-shaped transmission function. Embedding the helical phase converts the structure into a fork grating, while multiplication by the ring aperture ensures that the vortex beam produced in the first diffraction order evolves into a BGVB in the far field. The proposed holographic element was fabricated on a glass substrate using lithography, and illumination with a Gaussian beam of suitable waist generated a clear BGVB in the first diffraction order. The measured intensity profile shows excellent agreement with theoretical predictions. To determine the topological charge (TC), we employed an astigmatic grating with locally parallel grooves exhibiting second-order curvature. Introducing astigmatic aberration at an appropriate propagation distance produces elongated intensity fringes, and counting these fringes allows accurate determination of the TC. Numerical simulations and experimental measurements exhibit strong consistency, confirming the effectiveness of the proposed method.

کلیدواژه ها:

Holography-Based Method ، Bessel-Gaussian Vortex Beams (BGVBs) ، Helical Phase ، Topological Charge (TC) ، Astigmatic Grating