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The X-ray emission from hollow atoms produced by collisions of multiply charged ions accelerated by a short pulse laser with a solid or foil is studied theoretically. The possibility of obtaining a high conversion efficiency X-ray source in an ultrafast atomic process~;1 fs! is demonstrated using the multistep-capture-and-loss~MSCL! model. Such an X-ray source has a clear advantage for the spectral range around a few kiloelectron volts over the conventional K a X-ray source. Namely, the number of X-ray photons increases as the laser energy becomes larger and could reach 3 ϫ 10 11 photons for a laser energy of about 10 J.

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The soft x-ray emission fromHe-Iike and H-like were obtained by using the double nozzle gas-puff (Nitrogen, and Oxygen) target irradiated by the laser which delivered a laser energy of 50 mJ in 400 Ps pulse width. Efficient absorption of the incident laser energy into the double gas-puff target was demonstrated experimentally such as 15 %, and 29% for Nitrogen and Oxygen, respectively. The sub keV x-ray emission from He-3 (1s2-ls2p, ls2-ls3p, and is2-ls4p) lines are observed around the 0.4 nm wavelength region by using the double nozzle Argon gas-puff target irradiated by a 5 J ,i ns, 1 jtm laser. Using the gas-puff target irradiated by a femto-second laser pulse, highly ionized ions of Cr-, Fe-and Ni-like Kr at the 5-20 nm wavelength region have been observed in a laser produced plasma. However, the intensity of the x-ray emissions from double nozzle gas-puff target are lower than that from the single nozzle gas-puff targets, using the Krypton gas. Using xenon gas, the intensity of the x-ray emissions from double nozzle gas-pufftarget is equivalent to that from the single nozzle target.

The simulated results for the K x-ray satellite spectra in hollow Ar atoms in the article should be obtained without an extra multiplication factor of the fluorescence yield of L→K in Eq. ͑4͒. So Eq. ͑4͒ and lines between the top and that just above Eq. ͑5͒ in the right column on page 5005 should be replaced by the following: '' . . . time-integrated population for the state. The intensity I k for the kth K x-ray satellite line is given bywhere ⌫ L→K r is the radiative transition rate for the L→K E1 transition. In general the radiative transition rate for the X →Y E1 transition is expressed as . . . ''Consequently, Fig. 2 should be replaced by the figure given here. There are some differences between the present simulated spectra obtained without L→K and the previous one, such as small changes of relative intensities of the K x-ray satellite lines, the value of the magnitude of the intensity, and the value of n M for the strongest line among each group of satellite lines shown in the figure. However, these differences do not lead to serious discrepancies between the simulated and the experimental spectra. Therefore this change does not alter any of the physical considerations and conclusions of the article.We thank Dr. Moribayashi of the Japan Atomic Energy Research Institute ͑JAERI͒ for pointing out this error.FIG. 2. Theoretical K satellite spectra emitted from Ar hollow ions obtained with the MSCL model, and DFS transition energies starting from a KM 4 state whose population is unity at tϭ0. The value of the average rate ␥ c for the electron capture, and the number of M-shell spectator electrons n M in the configuration required for a state to give the largest intensity among lines in each group of satellite spectra, are given. The same symbols used in Fig. 1 to indicate each KL n L satellite line are used in this figure.