Laser spot control via plasma lensing in optically formed plasma channels

Laser plasma accelerators (LPAs) have potential to enable compact light sources and high energy linear colliders due to their extremely high acceleration gradients. Intense laser pulses are required which necessitates tight focusing to reach sufficient intensities and guiding in plasma channels to maintain intensity over the acceleration length. The laser pulse must be properly matched with the plasma channel to optimize the efficiency of the LPA and laser spot size is one of the important parameters. While the matched configuration is desired for guiding, the mismatched configuration leads to laser spot size oscillation during propagation, enabling the potential for spot size control in laser systems that are typically fixed. At the BErkeley Lab Laser Accelerator (BELLA) Center, we have studied laser spot size and mode evolution in plasma waveguides, specifically over the first few cms, using optical field-ionized plasma channels [1-2] to improve our understanding of lensing with plasma waveguides. Here we will present results on plasma lensing with optically formed plasma channels using the BELLA PW laser system.