In the previous example, we explored the basics of using a four-level two-electron model and performed a basic simulation test of the model. In this example we discuss a basic laser simulation employing this model.
A gain structure is placed in the simulation region. In conjunction, a low Q cavity of quality factor of around 400 at the lasing wavelength, 1500 nm, transmitting at the pump wavelength, 750nm, is placed around the thin gain material. The Pump is at 750nm, corresponding to the energy difference between the level 3 and level 0 (E3-E0). The source used is a CW source and for more information how to create one, please refer to the CW source page.The maximum amplitude of the pump is 1e6 V/m. In the post process, the data collected using the monitor placed at the output will have the light at 750 nm and 1500 nm filtered out.
Open the simulation file laser_simulation.fsp. Run the simulation and then run the script file laser_simulation_analysis.lsf. The plots below will be generated. Lasing dynamics can be observed from these plots. After around 6 ps, lasing turns on and we see the oscillation, then stabilizing.
The level population plot shows that levels 2 and 1 initially overshoot, but soon oscillate, then eventually reach steady state. From the zoomed in plot below, we see that small but sufficient population inversion is achieved to maintain lasing.