Coherent pulse propagation in a Nd: YLF laser amplifier

Transient amplification of short Nd-glass laser pulses (1.15 ps) in a Nd: YLF amplifier stage is investigated for small (≈20 nJ) and moderately large (1.4 μJ) input amplitudes. Coherent pulse reshaping, stretching (factor of 2.4) and corresponding spectral gain narrowing are studied as functions of amplification factor. Homogeneous broadening of the YLF laser transition at 1.054 μm is inferred from the approximately exponential decay of the trailing pulse wing. A quantitative analysis of the coherent propagation effect yields the dephasing time. T₂=0.90±0.05 ps, and a negligible inhomogeneous broadening of ≤5%. Pulses of duration ≥2.5 ps and energy ≥ 100μJ are shown to be feasible for a hybrid glass-YLF laser system with 15 Hz repetition rate.