Beam quality and coherence evolution impulsed lasers

Summary form only given. It is now well established that laser pulses, whose duration is not much larger than the transit time inside the cavity, undergo a beam-parameter evolution (concerning spot size, radius of curvature, far-field divergence, etc.) during the pulse life, from its beginning to its end. In practice, pulsed lasers, such as XeCl excimer lasers generate pulses making only a few transits inside the resonator. As a consequence, the steady state is seldom reached at the end of the pulse and the beam quality of the pulse is worse than that of a steady-state beam.