3D gain modeling of LMJ and NIF amplifiers

A 3D ray-trace model has been developed to predict the performance of flashlamp-pumped laser amplifiers. The computer program, written in C++, Includes a graphical display option using the Open inventor library, as well as a parser and a loader allowing the user to easily model complex multi-segment amplifier systems. It runs both on a workstation cluster at LLNL (using PVM), and on the T3E Gray at CEA. We will discuss how we have reduced the required computation time without changing precision by optimizing the parameters which set the discretization level of the calculation. As an example, the sampling of calculation points is chosen to fit the pumping profile through the thickness of amplifier slabs. We will show the difference in pump rates with our latest model as opposed to those predicted by our earlier 2.5D code AmpModel. We will also present the results of calculations which model surfaces (e.g. AR coatings on blastshields) and other 3D effects such as top and bottom reflector positions and reflectivity which could not be included in the 2.5D model. This new computer model also includes a fall 3D calculation of the amplified spontaneous emission rate in the laser slab, as opposed to the 2.5D model which tracked only the variation in the gain across the transverse dimensions of the slab. We will present the impact of this evolution of the model on the predicted stimulated decay rate and the resulting gain distribution. Comparison with most recent AmpLab experimental results will be presented, in the different typical NIF and LMJ configurations ("Diamond", "X", and '"Inner").