PHASE DYNAMICS IN NANOSECOND PULSED DYE-LASER AMPLIFICATION

We examine the evolution of the optical phase in a nanosecond-pumped d ye amplifier and show that the time-dependent gain introduces optical phase distortions. For the case of uniform pumping and weak input-beam intensity an analytic expression for the evolution of the optical pha se is derived. Even for a temporally symmetric pump pulse the amplifie d pulse has an asymmetric frequency spectrum caused by the contributio n of the fluorescence rate to the dynamics of the amplification proces s. When the injected beam is pulsed, the evolution of the optical phas e varies with the relative timing between the input and the pump pulse s. The model is tested against experimental results for an amplifier t hat uses DCM dye dissolved in dimethyl sulfoxide. The rms deviation be tween the measured and the calculated behavior of the instantaneous fr equency is less than 6 MHz.