We report the use of an atomic magnetometer based on nonlinear magneto-optical rotation with frequency modulated light (FM NMOR) to detect nuclear magnetization of xenon gas. The magnetization of a spin-exchange-polarized xenon sample (1.7 cm 3 at a pressure of 5 bar, natural isotopic abundance, polarization 1 %), prepared remotely to the detection apparatus, is measured with an atomic sensor (which is insensitive to the leading field of 0.45 G applied to the sample; an independent bias field at the sensor is 140 µG). An average magnetic field of ∼ 10 nG induced by the xenon sample on the 10-cm diameter atomic sensor is detected with signal-to-noise ratio ∼ 10, limited by residual noise in the magnetic environment. The possibility of using modern atomic magnetometers as detectors of nuclear magnetic resonance and in magnetic resonance imaging is discussed. Atomic magnetometers appear to be ideally suited for emerging low-field and remote-detection magnetic resonance applications.PACS numbers: 07.55. Ge,82.56.Dj,76.60.Pc Nuclear magnetic resonance (NMR) is a versatile technique for the study of structure and dynamics on both molecular and macroscopic scales, and on time scales from nanoseconds to hours. Spin-polarized 129 Xe (nuclear spin-1/2, magnetic moment µ ≈ −0.78 µ N , where µ N is the nuclear magneton) is particularly well suited for NMR and magnetic-resonance imaging (MRI) studies for several reasons. It is possible to polarize it using the laser-optical-pumping techniques [1] to a degree that is orders of magnitude higher than what is possible via thermal polarization in high-field magnets. In contact with various analytes, xenon displays a wide range of relative chemical shifts of up to several hundred ppm [2], which makes it an ideal probe of its local physiochemical environment. Finally, it has a long longitudinal relaxation time of several minutes or longer, even at low fields. Xenon can also be used in solution, and is especially soluble in organic solvents.An important recent development in NMR/MRI is the technique of remote detection [3,4], in which information about an analyte is transferred onto a mobile spinpolarized substance, and is then read out at a different location. This technique allows the separate optimization of the encoding and the detection environment. As the signal in this case is due to the net magnetization of the spin-polarized sample, the task becomes to read out this information efficiently and with high sensitivity. Detection using superconducting quantum interference devices (SQUIDs) [5] and atomic magnetometers [6] provides an alternative to the traditional techniques involving inductive detection. In addition to eliminating the need for a strong magnetic field for the detector, another advantage of these methods is that the time constant of the measurement in this case is limited by the longitudinal relaxation, which could be significantly slower than transverse relaxation limiting induction detection. SQUID detection has already proven useful in NMR experiments [7,8]...
Hyperpolarized 129 Xe can be used as a sensor to indirectly detect NMR spectra of heteronuclei that are neither covalently bound nor necessarily in direct contact with the Xe atoms, but coupled through long-range intermolecular dipolar couplings. In order to reintroduce long-range dipolar couplings the sample symmetry has to be broken. This can be done either by an asymmetric sample arrangement, or by breaking the symmetry of the spin magnetization with field gradient pulses. Experiments are performed where only a small fraction of the available 129 Xe magnetization is used for each point, so that a single batch of xenon suffices for the point-by-point acquisition of a heteronuclear NMR spectrum. Examples with 1 H as analyte nucleus show that these methods have the potential to obtain spectra with a resolution that is high enough to determine homonuclear J couplings. The applicability of this technique with remote detection is discussed.
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