Computational model for time development of the EM field in pulsed laser systems

摘要

A computational model, which describes EM field formation in a pulsed laser from a randomly generated initial spontaneous field inside the laser cavity has been developed. The model is based on a two-dimensional fast Fourier transform and describes a real laser system taking into account a lensing and a diaphragm effect of the laser rod. The laser cavity is described by five effective planes, which represent different laser cavity elements-the back and the front mirror, the Q-switch element and the laser rod. At each plane the EM field is calculated in real space and propagation between the planes is achieved in Fourier space by multiplication with an appropriate phase factor. The computational time needed for simulation of a realistic pulse formation is in order of minutes. The model can predict the shape and the integral energy of the pulse, its transverse profile at different distances from the front mirror (including near and far field) and beam divergence. The results of the model were found to be in good agreement with measured parameters for a Q-switched ruby laser system running in stable as well as unstable cavity configurations. The temporal shape of a laser pulse was measured and calculated not only for the ruby laser, but also for a Nd:YAG laser. It was found that FWHM of a pulse produced by ruby laser is three times longer than FWHM of a pulse produced by Nd:YAG laser.