Parameter Optimization of 1-D Multi-FM SSD on the NIF

This work investigates the parameters that affect 1-D Multiple Frequency Modulation (Multi-FM) Smoothing by Spectral Dispersion (SSD) on the National Ignition Facility and demonstrates that a high level of uniformity can be achieved using Multi-FM by employing an optimization procedure. The laser non-uniformity that directly drives an inertial confinement fusion target can imprint on the target's shell during the ablation process, leading to the exponential growth of non-uniformity leading to the shell's destruction. The SSD system mitigates imprint by causing the speckle pattern to evolve continuously, creating many statistically independent patterns that average over time. The 1-D Multi-FM SSD system uses multiple phase modulators with different frequencies in a single dimension. A MATLAB program was developed to optimize 1-D Multi-FM SSD by intelligently varying the parameters to minimize a metric based on time integrated laser non-uniformity and laser system constraints. The MATLAB program's algorithm is based on the Levenberg-Marquadt method to find optimal solutions based on local derivative values. The MATLAB program was able to produce realizations of 1-D Multi-FM SSD that have lower levels of non-uniformity compared to single modulator designs. The OMEGA-EP laser will be used as a test bed for the new designs