Generation of Small-Divergence Soft X-Ray Laser by Plasma Waveguiding with a Curved Target

Abstract
We have studied plasma waveguiding in soft x-ray laser experiments. A curved-slab target was used in order to compensate for x-ray refraction in a gradient-density plasma. In addition to significant increase in the x-ray laser intensity in single-pass amplification, a small beam divergence of less than 1 mrad has been stably generated in double-pass amplification with the curved target. The angular intensity distribution of the double-passed beam indicates that the x-ray laser has been amplified in a plasma waveguide.