@article{14012,
  abstract     = {Monochromatization of high-harmonic sources has opened fascinating perspectives regarding time-resolved photoemission from all phases of matter. Such studies have invariably involved the use of spectral filters or spectrally dispersive optical components that are inherently lossy and technically complex. Here we present a new technique for the spectral selection of near-threshold harmonics and their spatial separation from the driving beams without any optical elements. We discover the existence of a narrow phase-matching gate resulting from the combination of the non-collinear generation geometry in an extended medium, atomic resonances and absorption. Our technique offers a filter contrast of up to 104 for the selected harmonics against the adjacent ones and offers multiple temporally synchronized beamlets in a single unified scheme. We demonstrate the selective generation of 133, 80 or 56 nm femtosecond pulses from a 400-nm driver, which is specific to the target gas. These results open new pathways towards phase-sensitive multi-pulse spectroscopy in the vacuum- and extreme-ultraviolet, and frequency-selective output coupling from enhancement cavities.},
  author       = {Rajeev, Rajendran and Hellwagner, Johannes and Schumacher, Anne and Jordan, Inga and Huppert, Martin and Tehlar, Andres and Niraghatam, Bhargava Ram and Baykusheva, Denitsa Rangelova and Lin, Nan and von Conta, Aaron and Wörner, Hans Jakob},
  issn         = {2047-7538},
  journal      = {Light: Science & Applications},
  keywords     = {Atomic and Molecular Physics, and Optics, Electronic, Optical and Magnetic Materials},
  number       = {11},
  pages        = {e16170--e16170},
  publisher    = {Springer Nature},
  title        = {{In situ frequency gating and beam splitting of vacuum- and extreme-ultraviolet pulses}},
  doi          = {10.1038/lsa.2016.170},
  volume       = {5},
  year         = {2016},
}