Direct numerical simulation of quasi-three-level passive Q-switched laser

The Runge–Kutta method is used to solve numerically the rate equations of quasi-three-level passive Q-switched laser directly without any approximate treatment of these differential equations. The 946 nm self-Q-switched Cr,Nd:YAG laser is chosen for example to describe the details. The time-dependence of intra-cavity photon density is obtained and its detailed real-time changing process is reproduced in numerical solution. The curves of laser output parameters such as average output power, pulse width, repetition rate, pulse energy and peak power changing with different cavity conditions such as pump power, output coupler reflectivity, Cr,Nd:YAG crystal length, Nd3+ ion and Cr4+ ion concentrations are simulated according to direct numerical solution rather than analytical expressions. This direct numerical simulation method can be widely used to describe and optimize the quasi-three-level passive Q-switched laser theoretically.

Research Highlights► We solve the rate equations of quasi-three-level passive Q-switched laser directly. ► The real-time process of intra-cavity photon density is simulated and reproduced. ► The curves of laser output parameters changing with cavity conditions are plotted. ► This method can be used to optimize quasi-three-level passive Q-switched laser.