Tapered capillaries applied in laser wakefield acceleration

This paper presents realisation of linearly tapered capillary discharge waveguides (CDWs), manufactured using a femtosecond laser micromachining technique. Waveguiding of a low power, 50 fs duration laser pulse is demonstrated and, despite a slight mismatch of the laser focal spot size with respect to the capillary entrance size, efficient guiding of the Gaussian-shaped laser pulse is obtained. Energy transmission of 80% is obtained for optimal delay of the laser pulse arrival time with respect to the discharge current pulse.