The spatial contrast challenge for intense laser-plasma experiments

Achieving the highest peak intensity possible is a key requirement of a majority of laser-plasma experiments. This requires confining laser energy to a small volume. The experimental determination of the spatial focus distribution is therefore important, especially to connect theoretical and experimental results. In this paper, we revise a new method to evaluate the spatial performance of a laser focus. Obtaining low- and high-dynamic-range (LDR/HDR) images of the laser focus profile is described for a typical high-intensity laser setup, and present data from our case study. We compare standard evaluation procedures based on both images quantitatively and determine the accuracies and associated errors. A spread out intensity distribution below the detection limit of the LDR is observed in the HDR acquisition. Our evaluation reveals that only considering LDR can overestimate the enclosed energy as well as the peak intensity by factors of 1.5. With our method we estimate the required dynamic range for this case to 4 orders of magnitude. Our discussion sheds light on possible causes for the deteriorative effect to targets in the vicinity of the primary focal spot.