A theoretical study of the output coupler reflectivity effect on the characteristics of Er+3 laser pulse at passively q-switching

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The objective of this study deal the effect of the output coupler mirror reflectivity of laser system on behavior and characteristics (duration and energy) of erbium passive Q-switching laser pulse was studied theoretically. In the methods of the study, virtual passive Q-switching laser system consist of major elements such as erbium doped silica as an active medium, Cr+4: YAG crystal used as a saturable absorber, and the mirrors of resonator. Mathematical rate equations model has been used to describe the physical relationship between this element has been solved numerically by Rung - Kutta –Fehlberg method. The results showed regarding the pulse behavior, the increasing value of output coupler mirror reflectivity lead to decreasing of rising and falling time of pulse, so the emission of pulse occur in an advanced time. While regarding the pulse characteristics, the pulse was distinguishable by short duration and high energy, resulting high power of pulse when the output coupler mirror reflectivity increasing. Regarding of results discussion, the study attributes the results to a decrease of the initial and final population inversion density of active medium that results from the increasing value of output coupler mirror reflectivity. Therefore, it is possible to conclude in order to improve the characteristics of erbium passive Q-switching laser pulse; it is appropriate increase the value of output coupler mirror reflectivity within acceptable limits.