A multipass laser system for free-free experiments

A multipass laser system is being developed for an electron scattering apparatus that will be used for laser-assisted free-free electron scattering experiments. The basic idea is that a gated Pockels cell is used to rotate horizontally polarized light, in an injection mode, to vertically polarized light which is then trapped in a repetitive path using mirrors and a polarizing beam-splitter cube. A test bed has proved the feasibility of this technique: 20 passes have been observed with a 20\% loss per round trip; this would correspond to in an increase of a factor of 5 in data collection. The system is now being installed on the scattering apparatus with similar initial results; we will present a progress report on this multipass system. We hope to increase the efficiency of the system so that there is only 10\% loss per round trip in order to achieve an order of magnitude improvement in data collection compared to that of a single pass set up.