Luminescence and laser measurements an energy meter. Below the lasing threshold (approximately 1.2 mJ), the system exhibits primarily spontaneous emission. Once the threshold is exceeded, a rapid transition to stimulated emission occurs, characterized by a sharp increase in output power and a marked reduction in linewidth to around 7 nm. The laser power output from the plane mirror is about five times higher than that from the concave mirror, as expected, based on the ratio of mirror reflectivities.