Amplified spontaneous emission - Application to Nd : YAG lasers

Amplified spontaneous emission can seriously degrade the Q-switched perform ance of a strong four-level transition such as the 1.064 Irm Nd:YAG transit ion or can even prevent oscillation on a weaker quasi-four-level transition such as the 0.946-mu m Nd:YAG transition, To characterize, and thus be abl e to mitigate, amplified spontaneous emission, a closed-form model is devel oped. By employing a closed-form solution, the differential equations descr ibing both the evolution and decay of the upper laser manifold population d ensity can be solved exactly. An advantage of this model is the separation of the spectral and spatial portions of amplified spontaneous emission. Gai n measurements, as a function of time and pump energy, are compared with th e model and good agreement is found. With these principles in mind, a flash lamp-pumped Nd:YAG laser was designed to operate at 0.946 mu m. At room tem perature, a threshold of 12 J and a slope efficiency of 0.009 was achieved.