High-brightness soft X-ray generation under optimized laser-cluster interaction

High-brightness soft X-ray emissions are obtained by optimizing the interaction between high-intensity ultrashort optical pulses and Ar clusters. With only 100-mJ pump energy, the yield at 13.8 nm with 0.1-nm bandwidth reaches 0.3 mJ/pulse, while the yield in the spectral range of 11-20 nm reaches 12 mJ/pulse in 4π solid angle. The relation between optimal pulse durations and cluster sizes are found to conform with the nano-plasma expansion model, while the optimal pump beam size is related to the pulse contrast by the condition that prepulse ionization is sufficiently weak to preserve the local plasma density.