Improving the rising edge of the temporal contrast of PHELIX by spatial conditioning in an unfolded stretcher

We showcase a new, unfolded stretcher setup at the PHELIX facility that incorporates a beam expander for spatial conditioning of the rising edge in the temporal contrast. With this purely optical technique we are able to improve the rising-edge contrast from 10 -6 achieved with the standard, folded stretcher at PHELIX to 5.7⋅10 −10 ±0.2⋅10 −10 at −30 ps. By comparing between measurements and model predictions based on spectral-phase and -amplitude effects, we are able to determine limiting factors at PHELIX. Those indicate that the achieved improvement is sufficient to make other limiting factors, like the compressor, visible in the rising edge.