Generation of single-photon states with orbital angular momentum in the process of spontaneous parametric down-conversion in a cavityDinislam Turyikhanov, Andrey Shkalikov, Ilnur Latypov and Aleksey KalachevEPJ Web Conf., 161 (2017) 03018DOI: https://doi.org/10.1051/epjconf/201716103018