Speaker
Description
Focusing few-TW or even sub-TW laser pulses into a sub-mm-long, dense gas cell opens up opportunities for realizing laser wakefield acceleration of electrons with 100-nA-level currents driven by modern high-repetition-rate lasers. Although the use of pure nitrogen in the cell facilitates the routine generation of 10-MeV-scale electron beams, the strong ionization of nitrogen ions toward higher states and the resulting excessively high electron density in the axial region can lead to significant defocusing of the pump pulse, which tends to inhibit LWFA and cause the loss of high-energy electrons. Therefore, this study aims to improve the properties of electron beams from LWFA driven by a 1-TW pulse by varying the nitrogen concentration ratio ρ, ranging from 0% (pure helium) to 5%, in an N₂–He mixture filled into a 400-µm-long gas cell. Compared to the electron beams generated from the pure nitrogen cell, which exhibit pointing fluctuations of 4.5 mrad and 11.9 mrad in the horizontal and vertical directions, respectively, using an N₂–He mixture with a low nitrogen concentration of ρ = 0.5% significantly reduces the pointing fluctuation to 3.8 mrad in both directions. More importantly, this gas mixture facilitates the generation of more high-energy electrons, accompanied by a distinct peak consistently appearing at 10 MeV in the dispersed energy spectra—markedly different from the continuous spectra observed with the pure nitrogen cell. Therefore, introducing an N₂–He mixture with a low nitrogen concentration ratio into a sub-mm gas cell presents a promising approach to further enhance the properties of electron beams from few-TW LWFA, primarily by reducing beam pointing fluctuations and increasing the charge of high-energy electrons.
