An improved double-pulse non-normal incidence pumping geometry for transient collisionally excited soft X-ray lasers

In this manuscript an optimized pumping geometry for transient collisionally excited soft x-ray lasers is presented. In contrast to the standard scheme, where a nanosecond pre-pulse under normal incidence is assumed to provide the optimal plasma preparation and a picosecond pulse under grazing incidence performs the final heating-and excitation process, two picosecond pulses of equal duration under non-normal incidence are applied. Both pulses are produced in the front-end of the CPA pump laser. They are focused collinearly onto the target with the same spherical mirror under non-normal incidence, optimized for efficient traveling wave excitation for the main-pulse. X-ray lasing was achieved on Ni-like palladium (14.7 nm) at less than 500 mJ total pump energy on the target. This proves that this configuration is at least as favorable as the standard scheme, providing much simpler and more reliable operation. Moreover using this concept x-ray lasing was realized on Ni-like Samarium (7.3 nm)