Ultrafast 1 MHz vacuum-ultraviolet source via highly cascaded harmonic generation in negative-curvature hollow-core fibers

The vacuum ultraviolet (VUV) spectral region, covering approximately 6–15 eV, has a unique ability to probe physical and chemical processes.  This range of the electromagnetic spectrum is often used as an ionization source in angle-resolved photoelectron spectroscopy (ARPES) and photoionization mass spectrometry (PIMS), or to initiate chemical reactions relevant to atmospheric science in a controlled environment.  In the referenced paper, the authors demonstrate the efficient generation of coherent VUV laser light at MHz repetition rates using highly cascaded four-wave mixing processes in a negative-curvature hollow-core photonic crystal fiber, a patent-pending technology integrated within the KMLabs Hyperion VUV laser system. Both even and odd order harmonics are generated up to the 15th harmonic (69 nm, 18.0 eV), with high energy resolution of ~40 meV. In contrast to direct high harmonic generation, this highly cascaded harmonic generation process is possible at much lower peak intensities and therefore can operate at higher repetition rates, driven by a robust ~10 W fiber-laser system in a compact setup. Additionally, numerical simulations that explore the fundamental capabilities and spatio-temporal dynamics of highly cascaded harmonic generation are presented. The Hyperion VUV source can significantly enhance the capabilities of high resolution photoelectron spectroscopies of molecular and quantum materials, such as photoionization mass spectrometry, and time-, angle-, and spin-resolved photoemission.  The high MHz repetition rate from this source is also appealing for laser-assisted atom probe tomography experiments for increased imaging throughput. 

Read the full article:  https://doi.org/10.1364/OPTICA.395688.