ABSTRACT
The lack of available table-top extreme ultraviolet (XUV) sources with high enough fluxes and coherence properties has limited the availability of nonlinear XUV and x-ray spectroscopies to free-electron lasers (FELs). Here, we demonstrate second harmonic generation (SHG) on a table-top XUV source by observing SHG near the Ti M2,3 edge with a high-harmonic seeded soft x-ray laser. Furthermore, this experiment represents the first SHG experiment in the XUV. First-principles electronic structure calculations suggest the surface specificity and separate the observed signal into its resonant and nonresonant contributions. The realization of XUV-SHG on a table-top source opens up more accessible opportunities for the study of element-specific dynamics in multicomponent systems where surface, interfacial, and bulk-phase asymmetries play a driving role.
ABSTRACT
We report a straightforward beam splitter in the soft x-ray spectral range using a thin oxidized aluminum foil. As it allows us to monitor reliably shot-to-shot variations in energy and in energy distribution, this beam splitter is of high interest for the simultaneous use of diagnostics for soft x-rays sources. We measure a transmission of 0.5 and a reflectivity of 0.018 at 22.5° of incidence with a soft x-ray laser working at 32.8 nm. These values are in good agreement with the theory. As the theory predicts a reflectivity and a transmission of both 12% at 52.5° of incidence for 32.8 nm, it can also be useful for experiments that require the division and recombination of a beam, for instance, interferometry or pump-probe technique with an intense soft x-ray source.
ABSTRACT
High-density, collisionally pumped plasma-based soft-x-ray lasers have recently delivered hundreds of femtosecond pulses, breaking the longstanding barrier of one picosecond. To pump these amplifiers an intense infrared pulse must propagate focused throughout all the length of the amplifier, which spans several Rayleigh lengths. However, strong nonlinear effects hinder the propagation of the laser beam. The use of a plasma waveguide allows us to overcome these drawbacks provided the hydrodynamic processes that dominate the creation and posterior evolution of the waveguide are controlled and optimized. In this paper we present experimental measurements of the radial density profile and transmittance of such waveguide, and we compare them with numerical calculations using hydrodynamic and particle-in-cell codes. Controlling the properties (electron density value and radial gradient) of the waveguide with the help of numerical codes promises the delivery of ultrashort (tens of femtoseconds), coherent soft-x-ray pulses.