Pulse Propagation in a High-Gain Laser Amplifier: Pulse Waveform and Saturation
The resonant pulse propagation is applied to a high-gain helium xenon 3.5 μm laser amplifier with a partially homogeneously broadened lineshape, with emphasis on the saturation effect and pulse waveform. This problem has been studied in a linear gas laser amplifier for determining the line-shape parameters in the limited case when the spectrum of the incident pulse is narrow enough near and around the line-center frequency of the gain medium. Here, we shall find the formulas of resonant pulse propagation which are applicable to the general case, even if the width of the spectrum is comparable with or greater than the spectral width of the gain medium. Including the saturation, our particular interests are in the formulas of the incremental intensity gain at the pulse peak γI, the increments of the pulse delay time ∂T/∂z, and of the pulse duration ∂τ’/∂z per unit plasma length. Using the experimental results of the value of ∂T/∂z, we shall determine the saturation intensity Is of the gain medium. The value of Is, obtained by applying a quasi-CW treatment to pulse propagation, is compared with the above results.
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