A table-top near-edge
X-ray absorption fine structure (NEXAFS)
spectroscopy system consisting of a soft X-ray source and an integrated
spectrometer with a significantly improved resolution is presented.
The soft X-ray source is based on a long-term stable and nearly debris-free
picosecond laser-induced plasma generated in a pulsed krypton gas
jet target. Photon energies ranging from 250 to 1000 eV can be used
for the absorption spectroscopy of thin samples. The newly designed
spectrometer accomplishes a spectral resolution of E/ΔE = 1535 at 430 eV, being close to typical
synchrotron setups. Moreover, a simultaneous multi-edge analysis is
possible. The performance of the new system is demonstrated by investigating
the fine structure of the K- and L-absorption edges of various elements
(carbon, calcium, oxygen, iron, nickel, and copper) for different
types of samples. An excellent agreement with synchrotron spectra
is achieved.
Two methods improving the brilliance of laser-induced plasmas emitting in the extreme UV (EUV) and soft x-ray (SXR) regions were investigated, using three different gases (nitrogen, krypton, and xenon) from a pulsed gas jet. Utilizing a newly designed piezoelectric valve, up to almost ten times higher gas pressures were applied, resulting in increased target densities and thus, higher conversion efficiencies of laser energy into EUV and SXR radiation. Secondly, geometrically reducing the angle between the incoming laser beam and the observed plasma emission minimizes reabsorption of the emitted short wavelength radiation. Combining both methods, the source brilliance is increased by a factor of 5 for nitrogen. Furthermore, a compact EUV focusing system for metrological applications is presented utilizing the optimized plasma source. An energy density of 1 mJ/cm2 at wavelength λ = 13.5 nm in the focal spot of an ellipsoidal mirror is achieved with xenon as the target gas being sufficient for material removal of PMMA samples with an ablation rate of 0.05 nm/pulse.
We present a new nozzle design for an improved brilliance of laser-produced gas plasmas emitting in the soft X-ray and extreme ultraviolet spectral regime. A rotationally asymmetric gas jet is formed by employing two closely adjacent nozzles facing each other under the angle of 45°. The generated three-dimensional gas density distribution is tomographically analyzed using a Hartmann-Shack wavefront sensor. A comparison with numerical simulations accomplishes an optimization of the nozzle arrangement. The colliding gas jets create an optimized gas distribution with increased density, leading to a significant brilliance enhancement of the extreme ultraviolet, soft X-ray plasma.
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