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Nuclear spin rotates plane polarised laser light. Pic: www.rsc.org

Conventional liquid and solid relies on detecting the net dipolar magnetic field outside a spin-polarised sample, explain Michael Romalis and colleagues at Princeton University, New Jersey. However, this only offers the NMR spectroscopist limited structural and spatial information. As such NMR has been extended with elaborate techniques involving magnetic field gradients and spin correlations. Using a laser beam, which is by definition a polarised light source has provided a new avenue of research - optical NMR. However, until now, this has been limited to quantum dots and other specialists materials. Romalis and his colleagues hoped to extend optical NMR to a much wider field of research. They have carried out measurements on water and liquid xenon-129 that show an easily measurable effect on the plane of polarization of a laser beam by nuclear spins. This effect is most marked when heavy nuclei are present in a sample and the researchers suggest that optical NMR detection could be used to study complex molecules. They add that continuous two-dimensional imaging might be possible, which will provide unprecedented spatial resolution.

Research to improve signal to noise ratio, will allow this proof of principle to become a viable technique. Romalis and his team suggest several areas in which improvements might be made, for instance by decreasing the laser wavelength or using higher power lasers. They add that the sensitivity of rotation measurements might also be improved by using a multi-pass or an optical cavity system. In independent research, scientists including Dmitry Budker in Alexander Pines' lab at the University of California at Berkeley have developed a novel approach to magnetic resonance imaging detection based on optical atomic magnetometry. The success of their laser-based approach to MRI could lead to compact and even portable MRI scanners to complement the large, static machines present in many medical facilities.

"The next step would be to combine the power of NMR and optical spectroscopy and demonstrate optical detection of nuclear spins selectively excited in a high resolution NMR magnet," Romalis told SpectroscopyNOW.

Related links:

Nature, 2006, 442, 1021-1024
Romalis Page
Pines Page
Proc Natl Acad Sci, 2006, 103, 12668-12671

Source: SpectroscopyNow