PHOTOEXCITATION OF POTASSIUM 3s WINDOW RESONANCES M. Koide, F. Koike, M.-T. Huang, R. Welitz, B. DePaola,T. Nagata, S. Ohtani, Y. Azuma, Institute for Laser Science, University of Electro-communications, Chofu, Tokyo, Japan School of Medicine, Kitasato University, Sagamihara, Kanagawa, Japan Photon Factory, Institute for Materials Structure Science, KEK, Ibaraki, Tsukuba, Japan Physics Department, Kansas State University, Manhattan, Kansas, U.S.A Department of Science & Technology, Meisei University, Hino, Tokyo, Japan The photoion yield spectrum of K was measured over the 3s-np window resonance region. Striking differences were found compared to the Ar 3s window resonances. In K, the resonances are wide and 3s-4p excitation was strongly enhanced whereas 3s-np (n$B!f(B5) were sharply suppressed. Results were analyzed by performing MCDF calculation.