Truncated ionization injection with a chirp laser pulse in laser wakefield acceleration

The ionization injection in laser wakefield acceleration has been a promising injection scheme. Nevertheless, it usually produces electron beam with large energy spread because the ionization injection occurs continuously. By using particle-in-cell (PIC) simulations, we propose a method to truncate ionization injection process with a chirp laser pulse. Due to the dynamically evolving of the chirp laser pulse when it propagating in plasma, the ionization injection length can be decreased to a few hundred micrometers determined by the chirp parameter. As a result, a quasi-monoenergetic electron with the narrow energy spread can be produced. The energy spread is expected to be decreased further by optimizing the quadratic chirp parameter.