Study of Active Medium Length Effect on Characteristics of Passive QSwitching and Stokes with Anti-Stokes Pulse

Objective: To study the effect of active medium length on the characteristics of passive Q-switching pulses, Stokes pulses, and anti-Stokes pulses generated by laser-Raman medium interaction in optical systems, theoretically. Methods: The optical system consists of Nd+3:YVO4, PbWO4, and Cr+4:YAG as active mediums, Raman medium, and saturable absorber materials, respectively. The rate equations model has been used in the study, and the Rung-Kutta-Fehelberg numerical method was used to solve the rate equations. Finding: The result shows that, decreasing of the active medium length leads to emit high power pulses at advanced time. It also leads to increase in initial value and the maximum value of population inversion density, and leads to increase in the energy of passive Q-switching pulses, Stokes pulses, and anti-Stokes pulses. So the decreasing of the active medium length leads to decrease in the pulses duration and the final population inversion density. To increase the power of the three generated pulses, the length of the active medium used in the system must be decreased. Novelty: The characteristics of two pulses generated by Laser-Raman interaction (passive Q-switching pulse and Stokes pulse) have been of interest in some studies. This study investigates the effect of the active medium length on the characteristics of three pulses generated (anti-Stokes pulse with Stokes pulse as well as the passive Q-switching pulses) by the optical system rather than two pulses. Keywords: Laser; Nd+3 :YVO4; passive Q-­switching pulse; Stokes and anti-­Stokes pulses 1