Development and characterisation of gas-jet and discharge capillary targets for LWFA

Laser wakefield acceleration (LWFA) has emerged as a promising concept for the next generation of high energy electron accelerators. Target development and analysis is an important aspect in the further development of LWFA.
For short interaction length, high density LWFA schemes (up to several millimetres interaction length, plasma densities down to ~10¹⁸ cm³) gas-jet targets are used. These targets are analysed by a laser interferometry setup which can resolve phase shifts down to 4 mrad. Tomographic reconstruction enables detection of non-axisymmetrical defects in cylindrical nozzles and analysis of slit-nozzles and nozzles with an induced shock-wave density step.
For lower density and longer interaction length LWFA schemes, high laser intensity must be maintained over distances much longer than the Rayleigh length. Therefore laser guiding is necessary to counteract the diffraction induced divergence of the beam.
For this, a plasma channel is created inside a capillary via the concept of slow capillary discharge and characterised using an interferometric method. It is shown that the plasma channel has a refractive index profile suitable for laser guiding. As the first step, the pressure range and the time window in which guiding can occur are determined by guidance of a He-Ne laser. With the gained knowledge, laser guiding capabilities of a pulsed Ti:Sa laser are shown. The results show a broad, easy to realise parameter window for pressure and time in which a laser intensity transmission of above 75% is achieved.