Optical Nuclear-Spin Polarisation ONP

A well-known and important phenomenon in the area of nuclear-spin resonance (NMR) in gases, liquids, or solid samples is dynamic nuclear-spin polarisation (DNP) (see e.g. [M6]). This term refers to deviations of the nuclear magnetisation from its thermal-equilibrium value, thus a deviation from the Boltzmann distribution of the populations of the nuclear Zeeman terms, which is produced by optical pumping (Kastler [31]), by the Overhauser effect [32], or by the effet solide or solid-state effect [33]. In all these cases, the primary effect is a disturbance of the Boltzmann distribution in the electronic-spin system. In the Overhauser effect and the effet solide, this disturbance is caused for example by saturation of an ESR transition. Owing to the hyperfine coupling, a nuclear polarisation then results from coupled nuclear-electronic spin relaxation processes, whereby the polarisation of the electronic spins is transferred to the nuclear spins. 

Quantitatively, the characteristic parameter for ONP is either the amplification factor V = Mq/Mo -1, or the polarisation 

The mechanism of ONP is based on the hyperfine coupling and on the selection rules for intersystem crossing. In detail, it is complicated. We refer the reader to the relevant literature, which is cited in the article by Hausser and Wolf [29]. 

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