Based on the generalized Huygens-Fresnel principle, a far-field propagation model of a truncated Gaussian beam through Kolmogorov atmospheric turbulence is proposed. Two parameters, the far-field focal peak intensity and the corresponding mean power density, are used to characterize the energy of the laser beam's long-distance transmission. Furthermore, an optimal truncation of the launch window to maximize the system performance has been investigated by numerical simulation. Several new formulae showing the relationship between the coefficient of the optimal launch window truncation and the turbulence strength are presented, which agree well with the real situation over a considerable turbulence regime. Crown Copyright (C) 2012 Published by Elsevier Ltd. All rights reserved.