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.