Demonstration of x-ray amplifiers near the carbonKedge

The Ni-like 4d-4p laser scheme has been extended to wavelengths near the K absorption edge of carbon. A gain of 2.3 cm^-1 with a duration of 250 psec was observed in Ni-like Ta at 44.83 {} (a wavelength close to optimal for holographic imaging of live cells). Ni-like W produced a gain of 2.6 cm^-1 with a total of seven gainlengths of amplification at 43.18 {}. This is the first demonstration of an x-ray amplifier on the short-wavelength side of the carbon K edge, within the ``water window.'' Both lasers should be scalable to coherent power sufficient for holographic imaging and other applications.