Optical injection of electrons into a laser wakefield accelerator by colliding a strong drive laser pulse and an orthogonally propagating and perpendicularly polarized weaker injection pulse(-s) is investigated using 2D and 3D particle-in-cell simulations. Within this contribution, we will present recent results of improvement in the fundamental scheme with single injection pulse by its specific modifications. Low-intensity injection pulses can generate sub-femtosecond electron bunches. Introduction of a second injection pulse perpendicular to the plasma-wave-driving pulse leads to a decrease in emittance and increase in charge. Moreover, we suggest introducing the negatively chirped pulses to drive the accelerating plasma wave in the configurations with controlled injection. It is demonstrated that the negative chirp effectively suppresses the presence of the dark current which is generally difficult to control. Thus, it amends the electron bunch parameters considerably.
Low-energy-spread laser wakefield acceleration using ionization injection with a tightly focused laser in a mismatched plasma channel