Analysis of Spectral Limitations and Spectral Evolution in Short Pulse Amplification With a Regenerative Amplifier

This paper presents a new understanding of the gain narrowing mechanism in short-pulse amplification. Spectral and temporal bandwidth measurements of the amplified pulse, extracted from a chirped pulse amplification system, indicates clearly that gain narrowing occurs during the initial roundtrips in a regenerative amplifier, but during the later round trips, the pulse gains spectral bandwidth. This evolution of the pulse and its spectrum in a Nd:glass regenerative amplifier has been explained with a simulation code. The simulation is based on the Frantz-Nodvik model that has been generalized to a spectral domain and applied to Nd:glass, the active medium of the regenerative amplifier. The results also confirm the inhomogeneous gain profile of the active medium and the slow cross relaxation rates.