Electron injection in laser wake-field acceleration by using near critical layers

Highlights: • A method for enhancing trapped electrons in the laser wake-field acceleration in dilute plasma is proposed. • In addition to increasing the number of trapped electrons, this mechanism also reduces the energy broadening. • Transverse emittance of the trapped electron bunch in this mechanism decreased. -- Abstract: A method for enhancing trapped electrons in the laser wake-field acceleration in dilute plasma is proposed. In this method, a thin layer with near critical density is placed in front of the dilute plasma. Upon interaction of this layer with a short and high power laser pulse, a relatively large number of layer electrons are injected in dilute plasma. Some of these electrons are trapped in the wake-field of transmitted laser pulse. Particle in cell simulation is used to demonstrate this method. Simulations showed that in addition to increasing the number of trapped electrons, this mechanism also reduces the energy broadening.