Two methods of measuring the gain medium parameters of a laser are presented (Hodgson N and Weber H 1997 Optical Resonators–Fundamentals, Advanced Concepts and Applications (Berlin: Springer) pp 583–91). The first method used measured only the output power of the CO₂ laser (10.6 μm is the wavelength used) using three separate output couplers, each having different couplings. Once the three different output powers were measured, the results were used in the Rigrod equation to solve for two separate Rigrod equations knowing all the variables except for two unknowns; the small signal gain coefficient and the saturation intensity. The second method was a single-pass measurement where a very low power CO₂ laser was injected into the high power CO₂ laser in question. Power readings were made before and after the injection to determine the gain. Both methods agree with each other well, within 5%, for the small signal gain calculation, which provides confidence that the calculation for saturation intensity in the first method is correct as well.