Use of the prepulse technique to enhance the weak 18.2-nm laser line in neonlike selenium

We report strong lasing in selenium on the neonlike 3p ? 3s, J = 0 ? 1 transition at 18.2 mn when the prepulse technique of using a low-intensity prepulse before the main optical drive pulse is used to illuminate the selenium target. Without the use of the prepulse, this line is 2 orders of magnitude weaker. The usual J = 2 ? 1 lines at 20.6 and 20.9 nm are observed to dominate the spectra both with and without the use of the prepulse. These experiments may provide important clues to help our understanding of why the 18.2-nm line, which was predicted to dominate the laser output, was always observed weakly in previous experiments.