Amplified spontaneous emission-application to Nd:YAG lasers

Amplified spontaneous emission can seriously degrade the Q-switched performance of a strong four-level transition such as the 1.064 μm Nd:YAG transition or can even prevent oscillation on a weaker quasi-four-level transition such as the 0.946-μm Nd:YAG transition. To characterize, and thus be able to mitigate, amplified spontaneous emission, a closed-form model is developed. By employing a closed-form solution, the differential equations describing both the evolution and decay of the upper laser manifold population density can be solved exactly. An advantage of this model is the separation of the spectral and spatial portions of amplified spontaneous emission. Gain measurements, as a function of time and pump energy, are compared with the model and good agreement is found. With these principles in mind, a flashlamp-pumped Nd:YAG laser was designed to operate at 0.936 μm. At room temperature, a threshold of 12 J and a slope efficiency of 0.009 was achieved