The present work presents the analysis of a photonic device. Starting from a laser model, it is shown that, if a two-level simplification is used and both low pumping and no losses are assumed, a second-order control system model is obtained. This model no longer describes a laser, but only a photonic device. The system response to a step input is analyzed and the results are compared with experimental data obtained when pumping a neodymium crystal with a diode laser. Both theoretical and experimental results are then compared with the analyzed photonic device. A good qualitative agreement is shown between the analytical, experimental, and computational results.