Optimizing the density of Stark decelerated radicals at low final velocities: a tutorial review Dominik Haas, Sebastian Scherb, Dongdong Zhang and Stefan Willitsch EPJ Techn Instrum, 4 1 (2017) 6 Published online: 25 September 2017 DOI: 10.1140/epjti/s40485-017-0041-x