Temporal synchronization of GHz repetition rate electron and laser pulses for the optimization of a compact inverse-Compton scattering x-ray source

Abstract

The operation of an inverse-Compton scattering source of x-rays or gamma-rays requires the precision alignment and synchronization of highly focused electron bunches and laser pulses at the collision point. The arrival times of electron and laser pulses must be synchronized with picosecond precision. We have developed an RF synchronization technique that reduces the initial timing uncertainty from 350 ps to less than 2 ps, greatly reducing the parameter space to be optimized while commissioning the x-ray source. We describe the technique and present measurements of its performance.

Free-electron laser inverse-Compton interaction x-ray source

“…The rf receiver portion of the feed-forward system also serves as a general purpose synchronous rf diagnostic tool for visualization of signals from rf pickups on BPMs and high speed optical detectors for laser diagnostics. This system was a critical tool for the synchronization of laser and electron pulses at the inverse-Compton interaction point [31].…”

“…Measurement of the micropulse arrival times at the interaction point is confounded by several factors: high radiation backgrounds, the broad bandwidth of optical transition radiation, low OTR intensity at 3000 nm, the detection of low level IR light, detector bandwidth, etc. The approach for FELICIA compares the rf phase of the visible OTR from a copper mirror inserted into the electron beam with the visible coherent harmonic radiation (CHR) generated by the FEL as previously reported in [31]. Since the CHR is coaligned with the fundamental laser light, it is useful as both a transverse alignment aid and a temporal reference for synchronization.…”