Using an on-shot pulse duration diagnostic in an LPA driven FEL system to directly measure correlations between drive laser and electron beam properties

Laser-plasma-accelerators (LPAs) have emerged as a promising technology to overcome the gradient limitations in conventional accelerators. LPAs are being developed for a broad range of applications, including as a compact source of electrons for free-electron-lasers (FELs), which benefit from their inherently large peak currents and high transverse beam brightness. One of the challenges towards reliable LPA-driven FEL operation are the strict limitations imposed on the bunch properties by the undulator acceptance, which requires high shot-to-shot stability and precise tunability. In this work, we report on implementation of an on-shot diagnostic on the Hundred Terawatt Undulator (HTU) beamline at the BELLA center to directly correlate laser pulse temporal profile and spectral phase, important parameters impacting bunch generation, and stability with electron beam properties, transport, and the undulator performance. Thus, we are able to gain important insights into the underlying dynamics, bringing us closer to effectively matching the electron bunches to the FEL acceptance and thereby towards realizing an application ready LPA driven FEL.