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A measurement of the 2s 1͞2 -2p 3͞2 x-ray transition in trapped Li-like Bi 801 ions was made that resolved the 0.820 6 0.026 eV hyperfine splitting of the ͑1s 2 2s͒ F4,5 ground configuration, providing the first such measurement in a multielectron highly charged ion. The intensity ratio of the two components is shown to be a new electron density diagnostic. The statistically averaged 2788.139 6 0.039 eV energy of the 2s 1͞2 -2p 3͞2 transition provides the most accurate test of QED in a high-Z ion to date, demonstrating the need for including higher-order terms in the Lamb shift calculations. [S0031-9007(98)

We have demonstrated small signal gain saturation on several transient-gain Ni-like ion x-ray lasers by using a high-power, chirped-pulse amplification, tabletop laser. These results have been achieved at wavelengths from 139-203 A using a total of 5-7 J energy in a traveling-wave excitation scheme. Strong amplification is also observed for Ni-like Sn at 119 A. Gain of 62 cm(-1) and gL product of 18 are determined on the 4d-->4p transition for Ni-like Pd at 147 A with an output energy of 12 &mgr;J. A systematic evaluation of the laser driver parameters yields optimum beam divergence and small deflection angles of 2-5 mrads, in good agreement with simulations.

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Results from a detailed study using the Crystal Ball detector at the SLAC e+e storage ring SPEAR of the inclusive photon spectra from 1.8 X 106 i(t' and 2.2&& 106 J/P decays are presented. Radiative transitions from the P to the 1'2~o states are observed with photon energies of 126.0+0.2+4, 169.6+0.3 +4, and 258.4+0.4+4 Mev and branching ratios 8(i('~y X2, &, p) =(8.0%0.5+0.7)%, (9.0+0.5+0.7)%, and (9.9+0.5+0.8)%, respectively. Values for the natural linew'idths of the p states are obtained: I (p2 l 0)=0.8-4.9, &3.8, and 13-21 MeV, respectively (90% C.L.). Improved values are found for the branchmg ratios 8(g'~yg,) =(0.28+0.06)% and B(J//~yes,) =(1.27+0.36)%, and for the natural width I (g,) =11.524.5 MeV.

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Laboratory x-ray lasers are currently being studied by researchers worldwide. This paper reviews some of the recent work carried out at Lawrence Livermore National Laboratory. Laser action has been demonstrated at wavelengths as short as 35.6 Å while saturation of the small signal gain has been observed with longer wavelength schemes. Some of the most successful schemes to date have been collisionally pumped x-ray lasers that use the thermal electron distribution within a laser-produced plasma to excite electrons from closed shells in neon- and nickel-like ions to metastable levels in the next shell. Attempts to quantify and improve the longitudinal and transverse coherence of collisionally pumped x-ray lasers are motivated by the desire to produce sources for specific applications. Toward this goal there is a large effort underway to enhance the power output of the Ni-like Ta x-ray laser at 44.83 Å as a source for x-ray imaging of live cells. Improving the efficiency of x-ray lasers in order to produce saturated output with smaller pump lasers is also a goal of this work.