Effect of chirped pulse on electron acceleration in the inverse free-electron laser

Electron acceleration by a chirped laser pulse is studied numerically in the presence of helical magnetic wiggler in vacuum. The type of chirp is linear and positive. It is shown that for specific value of chirp parameter, inverse free-electron resonance condition can be maintained for longer duration and electron can gain much higher energy. It is shown that chirp parameter, the initial phase of laser and laser intensity have a strong influence on the electron acceleration