Quasimonoenergetic collimated electron beams from a laser wakefield acceleration in low density pure nitrogen

A laser wakefield acceleration (LWFA) experiment is performed using 30 TW, 30 fs, and 800 nm laser pulses, focused onto pure nitrogen plasma having relatively low densities in the range of 0.8×1018 cm−3 to 2.7×1018 cm−3. Electron beams having a low divergence of ∼3 mrad (full-width at half-maximum) and quasi-monoenergetic peak energies of ∼105 MeV are achieved over 4-mm interaction length. The total electron beam charge reached to 2 nC, however, only 1%–2% of this (tens of pC) had energies >35 MeV. We tried different conditions to optimize the electron beam acceleration; our experiment verifies that lower nitrogen plasma densities are generating electron beams with high quality in terms of divergence, charge, pointing stability, and maximum energy. In addition, if LWFA is to be widely used as a basis for compact particle accelerators in the future, therefore, from the economic and safety points of view we propose the use of nitrogen gas rather than helium or hydrogen.