Radiation collimation in a thick crystalline undulator Tobias Nyholm Wistisen, Ulrik Ingerslev Uggerhøj, John Lundsgaard Hansen, Werner Lauth and Pascal Klag Eur. Phys. J. D, 71 5 (2017) 124 Published online: 23 May 2017 DOI: 10.1140/epjd/e2017-70720-y