  We present a study of a very seldom used way of measuring magnetic domain
wall velocity, which makes it possible to have a real-time probing of the
domain movement in the area illuminated by a laser spot. We have compared this
method to the most usual one: although the velocities are similar, the
different method do not give the same results if the laser spot is too small.
It can be explained by a dendritic shape of the domain wall. By changing the
size spot, we propose a basic model which describes quite well the transit time
in the laser spot as a function of its size and makes it possible to extract
the velocity and the depth of the dendrites.
