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@ARTICLE{Sfke:828746,
      author       = {Süfke, Martin and Lehmkuhl, Sören and Liebisch, Alexander
                      and Blümich, Bernhard and Appelt, Stephan},
      title        = {{P}ara-hydrogen raser delivers sub-millihertz resolution in
                      nuclear magnetic resonance},
      journal      = {Nature physics},
      volume       = {13},
      issn         = {1745-2481},
      address      = {Basingstoke},
      publisher    = {Nature Publishing Group},
      reportid     = {FZJ-2017-02612},
      pages        = {568–572},
      year         = {2017},
      abstract     = {The precision of nuclear magnetic resonance spectroscopy1
                      (NMR) is limited by the signal-to-noise ratio, the
                      measurement time Tm and the linewidth Δν = 1/(πT2).
                      Overcoming the T 2 limit is possible if the nuclear spins of
                      a molecule emit continuous radio waves. Lasers and masers
                      are self-organized systems which emit coherent radiation in
                      the optical and micro-wave regime. Both are based on
                      creating a population inversion of specific energy states.
                      Here we show continuous oscillations of proton spins of
                      organic molecules in the radiofrequency regime (raser5). We
                      achieve this by coupling a population inversion created
                      through signal amplification by reversible exchange (SABRE)
                      to a high-quality-factor resonator. For the case of 15N
                      labelled molecules, we observe multi-mode raser activity,
                      which reports different spin quantum states. The
                      corresponding 1H-15N J-coupled NMR spectra exhibit
                      unprecedented sub-millihertz resolution and can be explained
                      assuming two-spin ordered quantum states. Our findings
                      demonstrate a substantial improvement in the frequency
                      resolution of NMR.},
      cin          = {ZEA-2 / IEK-9},
      ddc          = {530},
      cid          = {I:(DE-Juel1)ZEA-2-20090406 / I:(DE-Juel1)IEK-9-20110218},
      pnm          = {131 - Electrochemical Storage (POF3-131) / HITEC -
                      Helmholtz Interdisciplinary Doctoral Training in Energy and
                      Climate Research (HITEC) (HITEC-20170406)},
      pid          = {G:(DE-HGF)POF3-131 / G:(DE-Juel1)HITEC-20170406},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000402604200017},
      doi          = {10.1038/nphys4076},
      url          = {https://juser.fz-juelich.de/record/828746},
}