HIGH-GAIN X-RAY LASERS AT THE WATER WINDOW

We propose a scheme for producing a spatial and temporal averaged gain of 45 cm-1 in nickel-like Ta, including refraction. This result is achieved by irradiating a 40 mug/cm2 target with a low intensity pulse [2omega(lambda=0.53 mum), 5x10(13) W/cm2, 80 ps] to make the plasma subcritical. This is followed by a high intensity pulse (2omega, 2x10(15), 20 ps) to give the proper ionization. Therefore the principle of pulse shaping to achieve high gain using high intensity pump radiation is demonstrated.