Wavelengths of the Ni-like 4d1S0 - 4p1P1 x-ray laser line

We measure the wavelengths of the Ni-like 3d94d1S0 - 3d94p1P1 x-ray laser line in several low-Z Ni-like ions ranging from Y (Z=39) to Cd (Z=48). These wavelengths are compared with optimized level calculations using a multiconfiguration Dirac-Fock code. With the help of these results, we identify this line to very high accuracy in nonlasing plasmas from As (Z=33) to Mo (Z=42). Accurate values of these wavelengths are essential for performing plasma imaging and interferometry experiments with multilayer optics that use the x-ray laser to backlight other plasmas. These results also provide important atomic data that are currently missing about the energy of the 4d1S0 level in the NiI sequence. copyright 1998 The American Physical Society