Ultraviolet prepulse for enhanced x‐ray emission and brightness from droplet‐target laser plasmas

We show that an ultraviolet prepulse significantly enhances the water‐window x‐ray emission and brightness for a droplet‐target laser plasma. By combining a 65 mJ, 120 ps, λ=532 nm main pulse with an up to 3 mJ prepulse, the emitted x‐ray photon flux may be increased more than eight times. The resulting C VI λ=3.37 nm line emission is more than 3×1012 photons/sr⋅pulse, corresponding to a conversion efficiency above 3%/line. The integrated spectral brightness is increased two times and is found to reach its maximum for different prepulse parameters than those resulting in maximum photon flux.