BECKERT ERIK ET AL: 'A space-suitable, high brilliant entangled photon source for satellite based quantum key distribution', PROCEEDINGS OF SPIE, SPIE, 1000 20TH ST. BELLINGHAM WA 98225-6705 USA, vol. 10910, 4 March 2019 (2019-03-04), pages 1091016 - 1091016, XP060118830, ISSN: 0277-786X, ISBN: 978-1-5106-2687-4, DOI: 10.1117/12.2507603