Effect of the Cassegrain Telescope on the scintillation of Mathieu-Gauss beams

The scintillation index plays a crucial role in the performance of free space optics (FSO) and quantum key distribution (QKD) systems. Enhancement in the scintillation index causes an increase in the bit error rate and a decrease in the key rate. In this paper, we studied the effect of the Cassegrain telescope on the scintillation of Mathieu-Gauss beams (MGB) in a weak turbulent atmosphere. We model the atmosphere by using the random phase screen numerical approach. We benefit from the hard aperture function when modeling the telescope. We compare the point-like scintillation values with and without the Cassegrain telescope. We research even and odd modes of the MGB. We observe that the scintillation index decreases drastically when using the Cassegrain telescope. In addition, we investigate that the scintillation index decreases when the expansion order rises. Similarly, we see that there is an inverse relation between the first complex expansion coefficient at a short distance. An increase in the second complex expansion coefficient shows its advantage at longer distances by mitigating scintillation. We anticipate that our results will be useful for the optical engineers to design FSO and QKD systems.