Effect of laser contrast ratio on electron beam stability in laser wakefield acceleration experiments

Laser wakefield accelerators offer the possibility of compact electron acceleration. However one of the key outstanding issues with the results reported to date is the electron beam stability. Experiments on two laser systems reveal that the contrast ratio between the ASE pedestal and main pulse is an important factor in determining the quality of the electron beam. With a high contrast ratio (108) the electron beam profile is a well collimated single beam having a low pointing instability (< 10 mrad rms). With a lower contrast (10(6)) the beam profile contains multiple beamlets which exhibit a large pointing instability (similar or equal to 50 mrad rms). A high contrast ratio not only improves the beam pointing stability (similar or equal to 6 mrad) but also stabilizes the electron beam energy reproducibility (5%).