Diagnostics of the down-ramp gas and plasma density profiles in a gas jet and a capillary gas cell

Laser-aided plasma diagnostics is a very important tool for laser-driven plasma wakefield acceleration, where a gas jet or a gas cell is used to produce a plasma density of 1018∼1019/cm3. We developed special plasma sources based on a gas jet and a capillary gas cell with a sudden density down-ramp, which can induce easy self-injection of plasma electrons into the laser wakefield. In our research, the Mach-Zehnder laser interferometer with a Ti:sapphire laser of 40 fs pulse duration was used to diagnose the gas and laser-produced plasma densities in the gas jet and the capillary gas cell. The measurement results for the gas and plasma densities are reported in this paper.