We demonstrated a water-window (WW) soft x-ray (SXR) source using a regenerative liquid bismuth target irradiated by a solid-state laser. A tank filled with the solid Bi particles was heated by a band heater to make liquid Bi, and then it was pushed out from the nozzle by the nitrogen gas. A 1064-nm Nd:YAG laser with a pulse duration of 150 ps and a repetition rate of 10 Hz was irradiated to the liquid Bi target. We observed the time-integrated spectrum of SXR with a wavelength shorter than 6 nm using a spectroscopy and energy spectrum of the suprathermal ions emitted from the WWSXR source using a Faraday cup. The number of photons was observed to be about 1 ×1013
photons/nm·sr·pulse at a peak wavelength of 3.9 and 4.2 nm, and 0.4 ×1013 photons/nm·sr·pulse at a peak wavelength of 2.4 nm. The total number of photons emitted in 2.3 – 4.4 nm was about 1×1013 photons/sr·pulse. Suprathermal ions were also emitted with a maximum energy of 140 keV from the hot, dense Bi plasma. These results have the potential to use a short wavelength light source for next-generation lithography systems.
We have demonstrated the spatial separation of extreme ultraviolet (EUV) emission and energetic tin (Sn) ions as debris from a laser-produced plasma (LPP) with a double-laser-pulse irradiation scheme based on a plasma X-ray laser configuration. We used two Nd:YAG lasers operating at a wavelength of 1064 nm for pre- and main pulses. The pre-pulse at a laser intensity of 2×108 W/cm2 was irradiated to the Sn solid planar target to produce a pre-plasma. After 20 ns from pre-pulse irradiation, the main pulse at a laser intensity of 2×1011 W/cm2 was irradiated in a tangential direction to the pre-plasma. We observed the angular distributions of EUV emission and energetic ions using an X-ray diode and a Faraday cup. The EUV was slightly emitted toward the main pulse. On the other hand, energetic ions were emitted toward the prepulse side. Under similar conditions, charge-separated energetic Sn ions were measured using an electrostatic energy analyzer (ESA), and the maximum kinetic energy and maximum valence were reduced.
We evaluated the charge-separated energy spectra of the suprathermal highly charged gadolinium (Gd) ions as debris from a laser-produced plasma (LPP). Laser pulses with pulse durations of 6 ns and 150 ps were irradiated to a solid planar Gd target. Charge-separated suprathermal Gd ions from an LPP were measured using an electrostatic energy analyzer (ESA). The maximum ionic charge state was q = 16, and the maximum energy was about 30 keV (q = 16) at the pulse duration of 150 ps under the laser intensity of IL = 2 × 1012 W/cm2. At the pulse duration of 6 ns under the same laser intensity of IL = 2 × 1012 W/cm2 by a control of a laser pulse energy and a focal spot diameter, the maximum ionic charge state was q = 15, and the maximum energy was 15 keV (q = 10), approximately half of that in the case of the pulse duration of 150 ps.
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