ساره عبد الحسين شدودأ.د. عبد الكريم مهدي صالح النيازي2024-10-292024-10-292024-09-12https://dspace.utq.edu.iq/handle/123456789/142Based on models of rate equations of passive Q- switching which were prepared in previous studies and containing three or four equations. In this study, a proposal was made to formulate a model of coupled rate equations with six first-order differential equations to simulate the passive Q-switching technique in laser systems whose effective mediums are characterized by a range of spectral lines. That constitute more than a system of energy levels for those spectral lines as is the case of rare- earth element neodymium which doped YAG crystal (Nd +3: YAG). This model was tested in the utilization of neodymium ions spectral lines 4F3/2, 4I11/2 , 4I9/2, which constitute a four-levels energy system and the semi three-levels energy system for a single active medium with the crystal Cr+4: YAG as a saturable absorber material, using Rung-Kutta-Fahlberg numerical method in a software computer program prepared in this study. The results obtained showed a good agreement with concerning to the behavior and construction of both pulse photons, the behavior of population inversion density of active medium ions, and the temporal variation of saturable absorber energy level population with theoretical bases of passive Q-switching method, and the single pulse behavior generated by the use of previous equations models. This enhances the reliability of the physical basis and mathematical formula of the equations model. The effect of important essential parameters on the construction, generation, and characteristics of dual pulses generated has been studied. The results showed that the increasing of ions density of SA leads to an increase in the energy of the dual passive q-switching laser pulses, while the duration decrease as a function of ions density of the SA, which provides a high-power laser pulses. The results showed that the gradual buildup of both pulses and the pulses reached to maximum photons density in later time when the value of lam increase, The results also showed an increase in pulse duration and decrease in each other's energy and power while increasing the effective medium length. An increase in the length of the SA leads to the construction and release of pulses in advanced (earlier) time, decreased in their duration, and increased energy and the power of both pulses. The results showed the construction and release the pulses in late times as the value of output coupler mirror reflectivity increased, and the results showed the increase of energy and the power values of both pulses . The instantaneous temporal behavior of the absorption activity shown by the saturable absorber material toward the photons of both passive Q-switching pulses as a function of the ion's number density was studied. The results showed that the steady state of absorption activity or loss in the photons of both pulses within the cavity, and the state of optical bleaching which represents the conversion of absorbent material to transparent status in relation to its absorption of photons are occur at an advanced time with the increasing of ions number density of saturable absorber material ions.entext::thesis::doctoral thesis