Laser wakefield acceleration of 10-MeV-scale electrons driven by 1-TW multi-cycle laser pulses in a sub-millimeter nitrogen gas cell

By focusing conventional 1-TW 40-fs laser pulses into a dense 450-μm-long nitrogen gas cell, we demonstrate the feasibility of routinely generating electron beams from laser wakefield acceleration (LWFA) with primary energies scaling up to 10 MeV and a high charge in excess of 50 pC. When electron beams are generated with a charge of ≈30 pC and a beam divergence of ≈40 mrad from the nitrogen cell having a peak atom density of 7.6 × 10 18 cm-3, increasing the density inside the cell by 25% -controlled by tuning the backing pressure of fed nitrogen gas -can induce defocusing of the pump pulse that leads to a twofold increase in the output charge but with a trade-off in beam divergence. Therefore, this LWFA scheme has two preferred regimes for acquiring electron beams with either lower divergence or higher beam charge depending on a slight variation of the gas/plasma density inside the cell. Our results identify the high potential for implementing sub-millimeter nitrogen gas cells in the future development of high-repetition-rate LWFA driven by sub-TW or few-TW laser pulses.