Alignment of Pointing beam in the Optical Thomson Scattering Laser at the National ignition Facility

The National Ignition Facility (NIF), the world's largest and most energetic laser, employs 192 laser beams to achieve inertial confinement fusion by irradiating a mm scale fusion target. The optical Thomson scattering (OTS) laser is being deployed to probe the target and understand the target implosion physics using 3 omega and 5 omega probe beams. Understanding of the plasma physics will enable improvements of the fusion performance. OTS is a complex system employing many automated alignment loops. Centroid based approach is one of the common approaches for detecting the position of normal Gaussian beams within the OTS for beam alignment. However, due to several optical effects the alignment beam used for one of the pointing loops is shaped like a comet. The pointing beam exhibits a faint tail and a brighter head. Centroiding with a high threshold usually is able to select the brightest spot located within the head. However, there are cases when the brightest region moves around, in some cases the brightest spot appears in the tail, leading to an oscillation in the beam position with the current centroid-based detection scheme. The purpose of this work is to investigate approaches to find a suitable solution to this oscillation and implement a stable beam positioning algorithm.