Simultaneous acquisition of multi-nuclei enhanced NMR/MRI by solution-state dynamic nuclear polarization

Dynamic nuclear polarization （DNP） has become a very important hyperpolarization method because it can dramatically increase the sensitivity of nuclear magnetic resonance （NMR） of various molecules. Liquid-state DNP based on Overhauser effect is capable of directly enhancing polarization of all kinds of nuclei in the system. The combination of simultaneous Overhauser multi-nuclei enhancements with the multi-nuclei parallel acquisitions provides a variety of important applications in both MR spectroscopy （MRS） and image （MRI）. Here we present two simple illustrative examples for simultaneously enhanced multi-nuclear spectra and images to demonstrate the principle and superiority. We have observed very large simultaneous DNP enhancements for different nuclei, such as XH and 23Na, 1H and 31p, 19F and 31p, especially for the first time to report sodium ion enhancement in liquid. We have also obtained the simultaneous images of 19H and 31p, 19F and 31p at low field by solution-state DNP for the first time.

Optical nuclear spin polarization in quantum dots

Hyperfine interaction between electron spin and randomly oriented nuclear spins is a key issue of electron coherence for quantum information/computation. We propose an efficient way to establish high polarization of nuclear spins and reduce the intrinsic nuclear spin fluctuations. Here, we polarize the nuclear spins in semiconductor quantum dot(QD) by the coherent population trapping(CPT) and the electric dipole spin resonance(EDSR) induced by optical fields and ac electric fields. By tuning the optical fields, we can obtain a powerful cooling background based on CPT for nuclear spin polarization. The EDSR can enhance the spin flip–flop rate which may increase the cooling efficiency. With the help of CPT and EDSR, an enhancement of 1300 times of the electron coherence time can be obtained after a 10-ns preparation time.

Optical pumping nuclear magnetic resonance system rotating in a plane parallel to the quantization axis

A model of an optical pumping nuclear magnetic resonance system rotating in a plane parallel to the quantization axis is presented. Different coordinate frames for nuclear spin polarization vector are introduced, and theoretical calculation is conducted to analyze this model. We demonstrate that when the optical pumping nuclear magnetic resonance system rotates in a plane parallel to the quantization axis, it will maintain a steady state with respect to the quantization axis which is independent of rotational speed and direction.

Dynamic nuclear self-polarization of Ⅲ–Ⅴsemiconductors

Ⅲ–Ⅴ semiconductors exhibit dynamic nuclear self-polarization(DYNASP) owing to the contact hyperfine interaction(HFI) between optically excited conduction electrons and lattice nuclei. In the self-polarization process at a low temperature, electron spin state and the nuclear polarization(magnetization) exchange a positive feedback, increasing energy splitting of the conduction electron states, thereby a large nuclear polarization. This phenomenon was theoretically predicted previously for conduction electrons excited linearly and elliptically polarized light. The polarization of the conduction electrons was represented by a parameter α in a formula for nuclear polarization(Eq.(9) in Ref. [1]); however, the effect of external magnetic fields on the nuclear polarization was not considered. Therefore, this study introduces this effect by further extending the previous studies. Herein, α′represents the combination of the effects of elliptically polarized electrons and an external magnetic field, which is used in the equations presented in previous studies. When α′ = 0, a large nuclear polarization is obtained below critical temperature Tc, but no polarization occurs above Tc. When α′ > 0, the nuclear polarization is enhanced above Tc. Below Tc, the nuclear polarization follows a hysteresis curve when α′ is partially manipulated by adjusting the degree of the polarization of the exciting laser.