Recent progress of research on x-ray lasers at the institute of physics, CAS

The transient nature of x-ray laser is studied. For a drive pulse even as short as 500fs, the x-ray laser gain still shows a quasi-steady state behavior. A real transient nature can only be seen when the x-ray laser is driven by a laser pulse with a duration as short as tens of femtoseconds. A femtosecond laser pulse driven collisional Ne-like Ti x-ray laser at 32.6 nm is numerically investigated. By using the optimized drive pulse configuration, a gain of 40 cm(-1) can be generated from a 5 mm x 50 mum line focus using about 1 J pump energy. Effects of delay time on transient collisional excitation nickle-like x-ray lasers are investigated analytically using a simple model. The calculations show that the longer delay time can greatly relax the density gradient. Similarly, increasing the intensity of the short pulse or extending the duration can also raise the electron temperature, resulting in higher gain coefficient. Our results indicate that extending the short pulse duration is more efficient than that of increasing the intensity.