Research on physical processes of xenon hyperpolarization by spin-exchange optical pumping of rubidium atoms in the medium (1 - 3 W) pumping power range


Project Details


The project is devoted to the research and development of optical methods of hyperpolarization of nuclei of noble gas atoms(xenon, helium, etc.). In the hyperpolarized state, the nuclear spins of gas atoms are oriented in one direction, whichincreases the magnetic resonance signal by 4-8 orders of magnitude compared to the equilibrium distribution. One methodof hyperpolarization of noble gases is spin-exchange optical pumping, which consists in polarization of gas nuclear spins dueto interaction with alkali metal atoms (rubidium, cesium, etc.) polarized by optical radiation. The efficiency of this polarizationprocess critically depends on the power and spectral width of the pump radiation line. The emergence of powerful (>100 W)semiconductor lasers with a narrow generation line (~0.1 nm) allowed over the last decade to create commercially availablexenon polarization systems. However, such xenon polarizers do not fully meet all the needs of science and technology. Thisis primarily due to the high cost of such systems (> $100,000), which is primarily determined by the cost of a specializeddiode laser, which limits the prevalence of such systems, secondly, the large size and weight of such installations, and thirdly,such systems are designed to polarize large volumes of gas (~ 1 liter) for use in medicine for magnetic resonance imaging oflungs, brain and other living tissue. At the same time, there is a great need in hyperpolarized xenon for NMR spectroscopy instudies in chemistry, biology, and materials science in studying internal structure and properties of porous materials withnanometer-sized structures, micro and nanostructured materials, nanotubes, polymeric aerogels, modern battery electrodes,porous molecular, dipeptide, and other crystals. This type of research does not require a single large volume of polarized gasand a few tens of milliliters is sufficient for filling sample cuvettes for NMR spectroscopy with a characteristic volume of nomore than 5 ml. In this case, the degree of polarization of the gas and its concentration, as well as the possibility of using thegas immediately after polarization without the need for transportation come to the fore. Thus, an actual research topic is thedevelopment and optimization of methods for high-performance polarization of noble gases in relatively small volumes, which would allow the polarization of the gas in close proximity to the NMR spectrometer.Progress in the field of semiconductor lasers has led to the appearance of commercially available semiconductor amplifierscapable of producing narrowband radiation with wavelengths corresponding to the absorption lines of alkali metals (Rb D2 -780 nm, D1 - 795 nm, Cs - D2 852 nm, D1 894 nm) with powers up to 3 W. The use of such radiation allows highly effectivepolarization of several tens of milliliters of a noble gas. However, this raises a number of fundamental issues associated withthe need to optimize polarization conditions, primarily due to the fact that when reducing the characteristic size of the gascell in which the optical pumping and spin-exchange processes occur, the cell volume decreases as a cube of a given size,and the surface area of the cell as a square. This leads to the fact that the role of spin-relaxation processes increases andpolarization efficiency sharply decreases. That does not allow to create an effective polarizer of small gas volumes by simplescaling of the unit from 100 to 3 W. At the same time, published studies of the factors influencing the efficiency of spinexchangepolarization of noble gases for the medium power range (1 - 10 W) are extremely few and these studies arefragmentary.This project is aimed at studying the processes of spin-exchange interaction between noble gas atoms and rubidium vaporsexcited by narrow-band laser radiation in the 1 - 3 W power range in order to increase the efficiency of xenon hyperpolarization process. Particular attention will be paid to issues related to the practical possibility of creating a compact,highly efficient generator of hyperpolarized xenon for practical purposes of NMR spectroscopy.
Effective start/end date13.01.202231.12.2023


  • 1.03.SY OPTICS


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