Focal Fluctuations in the Hundred Terawatt Thomson Laser Plasma Accelerator at BELLA

Fast pointing jitter fluctuations in the focal point of high power laser systems can be detrimental for precision experiments and applications especially where more than one beam is involved.\^{A} Thomson scattering experiments on narrow energy spread MeV photon beams, with applications including nuclear nonproliferation, utilize two high power lasers with 2.7 and 0.6 J respectively (on target) at 5 Hz and \^{a}\textasciiperthousand \textyen 40 fs. Focal fluctuations are seen at $+$/- 10 \^{A}\textmu m (peak to valley) and 4 \^{A}\textmu m RMS on a spot size of 20 \^{A}\textmu m. We have used a kHz co-propagating laser to look at the fluctuation frequencies of both the electron drive laser and the scatter laser. Fluctuations caused by building and optic vibrations are observed in the 10 - 200 Hz range. This supports\^{A} identification of pointing jitter sources in the system, the correlation of both, and to inform future plans to actively stabilize the lasers.