Abstract

Near-threshold multimode laser dynamic are being studied to gain some insight into their noise characteristics. Previous studies of a class A dye laser system¹ showed that observed fluctuations were dominated by coherent, deterministic effects. Simple scaling arguments, based on this model, suggest that shortening the laser cavity should increase the relative importance of quantum fluctuations. Our study focuses on class B lasers (e.g., short-cavity dye and Ti:sapphire lasers), in which the cavity loss rate is of the same order as the spontaneous emission rate. Semiclassical equations are derived using Bloch and wave equations. For this system we may adiabatically eliminate the polarization but must retain both the electric field and inversion as dynamic variables. The inversion is then doubly expanded into both temporal and spatial modes. The high-frequency inversion modes are adiabatically eliminated. Finally, a Langevin noise term is added to the electric field-mode and inversion equations. An analysis of the turn-on dynamics of the laser is performed and compared to experimental results from our laboratory and to earlier analytical predictions.²

© 1991 Optical Society of America