Highly Directive 18.9 nm Nickel-like Molybdenum X-Ray Laser Operating at 150 mJ Pump Energy

We experimentally demonstrate that by longitudinally pumping 2 mm long molybdenum preformed plasma with high-intensity 475 fs duration laser pulse, a highly directive soft-x-ray laser at 18.9 nm wavelength is generated. The divergence of the beam is evaluated to be of the submilliradian order, and only requires a pump laser energy of 150 mJ.