Optical vortex generation by volume holographic elements with embedded phase singularity: Effects of misalignments

Based on the linear theory for optical vortex (OV) formation in volume holographic elements (HE) with embedded phase singularity (A. Bekshaev et al., Opt. Commun. 285 (2012) 4005), we analyze theoretically the OV-beams obtained when the incident Gaussian beam axis deviates from the optical axis of the HE. For different displacements of the incident beam with respect to the HE centre, the spatial characteristics of the diffracted beams and their evolution during the post-HE propagation are investigated numerically with allowance for the radiation extinction in the HE depth. A special attention is paid to behaviour of the beam centroid (centre of gravity) trajectory. The sensitivity of the generated OV-beam profile to the incident beam misalignments can be used for the output beam shaping and control, in particular, for compensation of the OV-beam distortions associated with the light extinction.