A High Efficiency Soft X-Ray Laser in the 25–30 nm Spectral Region

Abstract

This paper outlines a strategy to obtain a soft X-ray laser providing saturated output in the wavelength region 25–30 nm, pumped by a small-scale subnanosecond driver of energy below 50 J. We will briefly review the basic principles of collisional excitation pumping in neonlike plasmas and discuss the application of prepulse driving in low-Z element slab targets. We summarise the conclusions of detailed computer modelling performed for neonlike iron (Z=26, dominant lasing line at 25.5 nm). This modelling predicts a gain coefficient of ~7cm⁻¹ using driving energies of ≈15 Jcm⁻¹ (assuming a 400 ps pulse, line focused to 100 µm) and thus saturated output should be achievable by double passing a 2 cm long plasma. Preliminary results of an experiment aimed at obtaining a detailed understanding of the parameters of prepulse-created plasma are presented. These data reveal that the nature of the prepulse plasma strongly depends on the target material and their detailed analysis is expected to indicate not only the optimal pumping regime but also the preferred target characteristics.