For wave front distribution measurements of excimer laser radiation, a Hartmann–Shack wave front sensor with 40×30 subapertures and a field of view adapted to the lateral laser beam profile was utilized. The peak-to-valley wave front resolution is λ/12 and the dynamic range 100λ per subaperture at 248 nm. Time-averaged propagation characteristics were determined for several combinations of resonator configuration and laser medium from the ns down to the fs pulse length regime. Above that, time-resolved measurements were carried out on a KrF excimer laser, showing a reduction of the beam divergence during the laser pulse by a factor of 1.6. This transient behavior is discussed on the basis of a simple geometrical model. The theoretical results are in qualitative agreement with the experiment.