Time-dependent EM field characterization in pulsed lasers

The development of the EM field in pulsed solid-state lasers is analyzed with a two-dimensional fast-Fourier transform computational model. The model is designed to enable on-line characterization of the EM field starting from a randomly generated initial spontaneous field. The temporal variation of the laser beam quality together with the power spiking behavior is studied, showing sharp brightness peaks at the beginning of the free generated laser pulse. The instantaneous beam pattern is followed throughout the laser pulse duration. Some important characteristics of the formation of resonator modes are given and the influence of the mode competition on the formation of typical patterns in the integrated beam is analyzed. Intensity pattern oscillations which can be attributed to the previously observed vortex formation were clearly detected, showing well-defined oscillation frequencies of the local EM field, unrelated to transverse intermode beat frequencies. Experiments were carried out on an Er:YAG laser confirming the beam pattern formation and showing good agreement with the computational model.