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@ARTICLE{Fleischer:1021164,
      author       = {Fleischer, Simon and Lehmkuhl, Sören and Lohmann, Lars and
                      Appelt, Stephan},
      title        = {{A}pproaching the {U}ltimate {L}imit in {M}easurement
                      {P}recision with {RASER} {NMR}},
      journal      = {Applied magnetic resonance},
      volume       = {54},
      number       = {11-12},
      issn         = {0937-9347},
      address      = {Wien [u.a.]},
      publisher    = {Springer},
      reportid     = {FZJ-2024-00610},
      pages        = {1241 - 1270},
      year         = {2023},
      abstract     = {Radio-frequency Amplification by Stimulated Emission of
                      Radiation (RASER) is a promising tool to study nonlinear
                      phenomena or measure NMR parameters with unprecedented
                      precision. Magnetic fields, J-couplings, and chemical shifts
                      can be recorded over long periods of time without the need
                      for radiofrequency excitation and signal averaging. One key
                      feature of RASER NMR spectroscopy is the improvement in
                      precision, which grows with the measurement time, unlike
                      conventional NMR spectroscopy, where the precision increases
                      with. However, when detecting NMR signals over minutes to
                      hours, using available NMR magnets (ppb homogeneity), the
                      achieved frequency resolution will eventually be limited by
                      magnetic field fluctuations. Here, we demonstrate that full
                      compensation is possible even for open low-field
                      electromagnets, where magnetic field fluctuations are
                      intrinsically present (in the ppm regime). A prerequisite
                      for compensation is that the spectrum contains at least one
                      isolated RASER line to be used as a reference, and the
                      sample experiences exclusively common magnetic field
                      fluctuations, that is, ones that are equal over the entire
                      sample volume. We discuss the current limits of precision
                      for RASER NMR measurements for two different cases: The
                      single-compartment RASER involving J-coupled modes, and the
                      two-compartment RASER involving chemically shifted species.
                      In the first case, the limit of measurable difference
                      approaches the Cramér-Rao lower bound (CRLB), achieving a
                      measurement precision Hz. In the second case, the measured
                      chemical shift separation is plagued by independently
                      fluctuating distant dipolar fields (DDF). The measured
                      independent field fluctuation between the two chambers is in
                      the order of tens of mHz. In both cases, new limits of
                      precision are achieved, which paves the way for sub-mHz
                      detection of NMR parameters, rotational rates, and
                      non-linear phenomena such as chaos and synchrony.},
      cin          = {ZEA-2},
      ddc          = {620},
      cid          = {I:(DE-Juel1)ZEA-2-20090406},
      pnm          = {622 - Detector Technologies and Systems (POF4-622)},
      pid          = {G:(DE-HGF)POF4-622},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:001064997700002},
      doi          = {10.1007/s00723-023-01597-w},
      url          = {https://juser.fz-juelich.de/record/1021164},
}