PHASE DYNAMICS IN NANOSECOND PULSED DYE-LASER AMPLIFICATION

We examine the evolution of the optical phase in a nanosecond-pumped dye 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 phase is derived. Even for a temporally symmetric pump pulse the amplified pulse has an asymmetric frequency spectrum caused by the contribution of the fluorescence rate to the dynamics of the amplification process. When the injected beam is pulsed, the evolution of the optical phase varies with the relative timing between the input and the pump pulses. The model is tested against experimental results for an amplifier that uses DCM dye dissolved in dimethyl sulfoxide. The rms deviation between the measured and the calculated behavior of the instantaneous frequency is less than 6 MHz.