Planar Laser-Induced Fluorescence For Custom Laser Plasma Accelerator Targets*

The ability to precisely shape gas jets for controlled injection of electrons in laser plasma accelerators (LPAs) is crucial for developing high quality electron beams. Verifying tailored density profiles has called for more detailed gas density diagnostic than those traditionally used.  Most diagnostics give line-of-sight measurements, integrating over and blurring sharp or asymmetric features. In this study, planar laser-induced fluorescence (PLIF) has been prototyped for characterizing laser plasma accelerator gas jet targets. PLIF has the distinct advantage of isolating a 2-D slice of the jet plume using a laser sheet providing more direct density information at regions of interest. This sheet can be scanned across the jet to map out the entire 3-D gas plume profile. It was shown that PLIF is able to resolve critical features such as gas density shocks.  Blade-in jets under low vacuum were characterized with PLIF and found to change drastically in character with blade position. Changes included change in the axis of the entire gas plume as well as its effective Mach number.