Focal spot smoothing by amplification of reduced coherence pulse in the high-power Nd-glass Phebus laser

The Nd-glass Phebus laser has the capability of delivering 2 X 10 kJ in a 1.3 ns pulse when using the usual narrow band oscillator. For the purpose of focal spot smoothing the coherence of the pulse is reduced by injecting the beam of a 1 nm bandwidth oscillator into a step index optical fiber. The use of the optical fiber at the laser front end changes the common point laser source into an extended source. The required optical arrangement taking into account the divergence of the extended source beam is described. The smoothing efficiency is measured by the reduction of one order of magnitude of the contrast of the energy modulations in the focal spot. It is experimentally established that non linear effects limit the power density in the amplifying medium to a value depending on the geometrical extension of the source. The identification of the relevant non linear effects is discussed.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.