The goal of this thesis is to take into account the gain saturation that occurs within pulse duration for actively node-locked lasers and to discuss its effects on the generated pulses. The population inversion, obtained analytically using a perturbation scheme, has been found to vary considerably within pulse envelope. An assumingly Gaussian pulse has been followed along its round-trip in the laser cavity through the active medium and the modulator, and by incorporating the time-dependent gain for the first time in the analysis, self-consistency relations have been found. The resulting pulse characteristics* based on typical Nd:YAG laser parameters show a strong dependence of the output pulsewidths on the pump intensity. as well as of the interpulse spacing on the length of the active medium. The population inversion droped by two orders of magnitude within the duration of the incoming pulse and the extent of the depletion was increasing for increasing pump intensities. By varying the input field from 1 up to 1.5x1 V/m the pulsewidth was found to vary from 1.4 to 2.1 psec while the interpulse spacing jittered within 1.7 psec for variations of the length of the active medium from 1 cm to 5 cm.