Switching the sign of the topological charge of vortex beams via changing the fork grating resolution

We demonstrate the effect of the resolution of forked-diffractive optical elements (DOEs) on the helicity of the topological charge (TC) of the orbital angular momentum (OAM) beams. To aim that, the forked-DOEs are designed with the same TC while they are different in resolution. Changing the resolution allows the fork direction to be switched. Interestingly, switching the sign of the TC is the consequential achievement for the OAM beams, generated by the fork grating elements with specific resolutions. Furthermore, changing the resolution make the fork gratings to be designed for generating petal-like beams in which the magnitude of the TC tends to zero. Finally, three criteria are calculated for all intensity distributions to quantify the generated beams' quality and investigate where the helicity of the TC changes. Consequently, we demonstrate the emphasis on selecting the resolution of DOEs which plays a pivotal role in optical systems, for instance in optical tweezers where the OAM beams need to be generated with a desired sign of TC.

Automated summary

In this study, we demonstrate the control of the TC helicity of OAM beams by changing the resolution of forked-DOEs. By adjusting the resolution, the fork direction and the sign of TC can be switched. Moreover, changing the resolution allows the design of petal-like beams with TC approaching zero. The research highlights the importance of selecting the appropriate resolution of DOEs in optical systems.