ABSTRACT
M.. Tanaka, M. Nishikino, T. Kawachi, N. Hasegawa, ML Kado, M.. Kishimoto, K. Sukegawa, Y. Ochi, K. Nagashima, Y. Kato Advanced Photon Research Centre, Japan Atomic Energy Research Institute, 8-1-1-2, Umemidai, Kizu-cho, Souraku-gun, Kyoto, 619-0215, Japan
1. Introduction Recently, x-ray lasers are extensively used as soft x-ray sources for several measurements, such as soft x-ray scattering [1] and interferometry [2, 3]. For these measurements, pulse duration, intensity and coherence of the x-ray laser are important. The transient collisional excitation (TCE) x-ray lasers have been intensively studied, because they can achieve a high gain of a few tens per centimeter [4, 5] and picosecond pulse duration [6, 7] using a tabletop laser system. However, the beam divergence of the TCE x-ray laser is large and spatial coherence is quite low, due to refraction from the density gradient of the plasma and the large Fresnel number of the gain medium.
