Optical diagnostics on capillary waveguides for extension of laser wakefield acceleration lengths

The electron beams produced from laser wakefield acceleration (LWFA) have been proposed for next generation electron accelerators and can be used for applications in imaging, microwave generation, and x-ray generation. The diffraction length achievable for LWFA can be extended by guiding the focused laser pulse using external guiding structures. This length is a fundamental limitation on the acceleration length and therefore maximum attainable electron energy. Capillary waveguides are used to setup guiding structure by creating a discharge plasma along the direction of laser propagation with varying plasma density radially. Two different waveguide schemes are being explored on the Hercules laser system (Ti:Sapphire, 30 fs, recently upgraded to 300 TW) - a purely ablative capillary discharge and a gas filled capillary discharge. The two schemes provide a range of differing characteristics such as lifetime, ionization state, and complexity. Diagnostics indicate that high intensity can be sustained over a few centimeters, with acceptable laser depletion.