title: On the tuning of high-resolution NMR probes.
abstract: Three optimum conditions for the tuning of NMR probes are compared: the conventional tuning optimum, which is based on radio-frequency pulse efficiency, the spin noise tuning optimum based on the line shape of the spin noise signal, and the newly introduced frequency shift tuning optimum, which minimizes the frequency pushing effect on strong signals. The latter results if the radiation damping feedback field is not in perfect quadrature to the precessing magnetization. According to the conventional RLC (resistor-inductor-capacitor) resonant circuit model, the optima should be identical, but significant deviations are found experimentally at low temperatures, in particular on cryogenically cooled probes. The existence of different optima with respect to frequency pushing and spin noise line shape has important consequences on the nonlinearity of spin dynamics at high polarization levels and the implementation of experiments on cold probes.
authors.affiliation: Institute of Organic Chemistry, Johannes Kepler University Linz, Altenbergerstraße 69, 4040 Linz (Austria), Fax: (+43) 732-2468-8747.
authors.forename: Maria Theresia
authors.initials: MT
authors.lastname: Pöschko
authors.forename: Judith
authors.initials: J
authors.lastname: Schlagnitweit
authors.forename: Gaspard
authors.initials: G
authors.lastname: Huber
authors.forename: Martin
authors.initials: M
authors.lastname: Nausner
authors.forename: Michaela
authors.initials: M
authors.lastname: Horničáková
authors.forename: Hervé
authors.initials: H
authors.lastname: Desvaux
authors.forename: Norbert
authors.initials: N
authors.lastname: Müller
keywords: NMR spectroscopy; analytical methods; magnetic properties; radiation damping; spin noise