The researchers in Heidelberg made various conceptional and experimental tricks in order to detect the time dilation at fast moving ions.

One trick is to prepare the ions as the moving observer (with a velocity of six percent of the speed of light in vacuum) and to use as a source a laser whose frequency can be varied and propagates head-on with the ions. A second laser beam with fixed frequency propagates in the same direction as the ion beam.

By these tricks one is able not only to focus the ions with a single fixed velocity, but is also capable to discriminate the Doppler effect from the relativistic effect by the anti-parallel configuration of the two lasers.