Speaker
Description
We present progress towards the realization of a coherent extreme ultraviolet (XUV) beamline at IMDEA Nanociencia that images nanoscale phase textures in quantum materials with femtosecond temporal resolution. This is achieved by combining high-harmonic generation (HHG)¹ with coherent imaging methods². The beamline will deliver monochromatized, polarization-controlled XUV radiation for coherent imaging experiments, overcoming the time restrictions of large-scale facility beamtimes and enabling a great control over the experimental conditions, as well as providing a test platform for optimization prior to synchrotron or XFEL experiments.
The driving laser is an Astrella HE amplifier delivering 30 fs pulses at 800 nm with 10 W average power at 1 kHz. These pulses are spectrally broadened in a gas-filled hollow-core fiber (HCF)³ and compressed down to 5 fs, leading to an HHG XUV supercontinuum. This generated supercontinuum, in combination with subsequent stages of the beamline, leads to a fully tunable XUV source. Polarization control of the XUV is achieved by generating circularly polarized HHG via a counter-rotating circularly polarized crossed-beam geometry⁴. To maximize harmonic efficiency in the non-collinear geometry, opposite-sign pulse-front tilts are introduced to the crossing beams to compensate temporal walk-off and improve the spatiotemporal overlap on the HHG target⁵. To this end, we designed a four-wedge compressor combining highly dispersive and birefringent low-dispersive media, allowing us to obtain angular dispersion that remains linear across the full bandwidth, while improving polarization purity. As a result, this approach produces the required spatial chirp for walk-off compensation without compromising few-cycle post-compression using commercially available double-chirped mirrors (DCMs), and avoids the significant energy losses associated with grating-based schemes.
In the next stage, the generated harmonics will be monochromatized using a time-and-polarization-preserving monochromator⁶, delivering tunable XUV radiation with ~250 meV bandwidth, targeting X-ray absorption fine-structure resonances, primarily at the Mn M-edge (~50 eV, ~25 nm) and Fe M-edge (~55 eV, ~22.5 nm). Finally, the beam will be delivered to a scattering chamber equipped with a cryogenically cooled sample manipulator, enabling temperature-controlled resonant scattering and imaging with in situ alignment and external field compatibility. A final spatial resolution of 25 nm and temporal resolution of 50 fs are targeted.
Our beamline will provide a tabletop source of tunable, narrowband (250 meV), polarization-controlled coherent XUV radiation with ultrafast temporal resolution (~50 fs), enabling resonant imaging of a wide variety of quantum materials.
1 Corkum, P. B. et al. Nature Physics, 2007, 3, 381–387.
2 Johnson, A. S. et al. Science Advances, 2021, 7, eabf1386.
3 Travers, J. C. et al. Nature Photonics. 2019, 13, 547–554.
4 Hickstein, D. et al. Nature Photonics, 2015, 9, 743–750.
5 Hernández-García, C. et al. Physical Review A, 2016, 93.4, 043855.
6 Poletto, L. et al. Applied Optics, 2010, 49, 5465–5473.