The dynamics of transverse mode formation time in positive-branch unstable resonators with low magnification (M = 1.32) and typical Fresnel numbers (279 < NT < 2700) used in high-energy lasers has been investigated. The objective was to observe the far-field intensity distribution from the onset of pumping to the settled steady-state diffraction-limited pattern. The research consisted of an experimental and numerical analysis. The experimental measurements of mode formation time were with a pulsed XeF laser having centered resonator optics. Mode formation was deduced from observation of the far field. The analytical effort consisted of a fast Fourier transform wave optics code which modeled the far-field pattern evolution. Results agree with temporal mode formation geometrical predictions of Ananev when laser saturation is achieved around this time.
R. William Jones and James F. Perkins, "Transverse mode formation in low-magnification positive-branch unstable resonators," Appl. Opt. 23, 1361-1368 (1984)