A quasi-supercontinuum source in the extreme ultraviolet (XUV) is demonstrated using a table-top femtosecond laser and a tunable optical parametric amplifier (OPA) as a driver for high-harmonic generation (HHG). The harmonic radiation, which is usually a comb of odd multiples of the fundamental frequency, is generated by near-infrared (NIR) laser pulses from the OPA. A quasi-continuous XUV spectrum in the range of 30 to 100 eV is realized by averaging over multiple harmonic comb spectra with slightly different fundamental frequencies and thus different spectral spacing between the individual harmonics. The driving laser wavelength is swept automatically during an averaging time period. With a total photon flux of 4×109 photons/s in the range of 30 eV to 100 eV and 1×107photons/s in the range of 100 eV to 200 eV, the resulting quasi-supercontinuum XUV source is suited for applications such as XUV coherence tomography (XCT) or near-edge absorption fine structure spectroscopy (NEXAFS).
Scientific and technological progress depend substantially on the
ability to image on the nanoscale. In order to investigate complex,
functional, nanoscopic structures like, e.g., semiconductor devices,
multilayer optics, or stacks of 2D materials, the imaging techniques
not only have to provide images but should also provide quantitative
information. We report the material-specific characterization of
nanoscopic buried structures with extreme ultraviolet coherence
tomography. The method is demonstrated at a laser-driven broadband
extreme ultraviolet radiation source, based on high-harmonic
generation. We show that, besides nanoscopic axial resolution, the
spectral reflectivity of all layers in a sample can be obtained using
algorithmic phase reconstruction. This provides localized,
spectroscopic, material-specific information of the sample. The method
can be applied in, e.g., semiconductor production, lithographic mask
inspection, or quality control of multilayer fabrication. Moreover, it
paves the way for the investigation of ultrafast nanoscopic effects at
functional buried interfaces.
Time-and angle-resolved photoemission spectroscopy of solids in the extreme ultraviolet at 500 kHz repetition rate Review of Scientific Instruments 90, 023104 (2019);
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