Ultrahigh-gain Ni-like Kr soft X-ray laser by optical-field-induced-ionization initiated transient excitation scheme Y. Nagata, O. Maya, M. Obara, Y. Aoyagi et K. Midorikawa J. Phys. IV France, 11 PR2 (2001) Pr2-193-Pr2-196 DOI: 10.1051/jp4:2001236