4.7. Laser Diagnostics

A suite of laser diagnostics is in place to provide data on the performance (i.e., power, energy, etc.) of NIF on each shot. The data from individual beams are used to determine the total power and energy and the power and energy balance on any given shot. The diagnostics have been designed to be consistent with the requirement that the rms power imbalance be 8% or less for a 1.8 MJ ≈20 ns total duration ignition pulse. The rms energy balance for that pulse is on the order of 5%. The power and energy balance for different pulse shapes and energies will vary slightly. To accurately measure power and energy balance, the 3ω power is measured to within 4% and the 3ω energy to within 3%.

For each quad on NIF, we have one power sensor in the input sensor diagnostic package (ISP), two 1ω power sensors at the output sensor package (OSP) and one 3ω power sensor in the 3ω drive diagnostic package. Thus, we get a direct measurement of the 3ω power vs time on a quarter of the NIF beams. 3ω power for other beams in a quad is derived using the 1ω power sensor data (from ISP or OSP) and flowing this forward to the 3ω power using LPOM calculations. The flow-forward power is then normalized to the measured 3ω energy. This data is then used to deduce 3ω power accuracy and power balance.