Ajoy A, Nazaryan R, Druga E, Liu K, Aguilar A, Han B, Gierth M, Oon J T, Safvati B, Tsang R, Walton J H, Suter D, Meriles C A, Reimer J A, Pines A
Department of Chemistry and Materials Science Division, Lawrence Berkeley National Laboratory, University of California Berkeley, Berkeley, California 94720, USA.
Nuclear Magnetic Resonance Facility, University of California Davis, Davis, California 95616, USA.
Rev Sci Instrum. 2020 Feb 1;91(2):023106. doi: 10.1063/1.5131655.
Dynamic Nuclear Polarization (DNP) is a powerful suite of techniques that deliver multifold signal enhancements in nuclear magnetic resonance (NMR) and MRI. The generated athermal spin states can also be exploited for quantum sensing and as probes for many-body physics. Typical DNP methods require the use of cryogens, large magnetic fields, and high power microwave excitation, which are expensive and unwieldy. Nanodiamond particles, rich in Nitrogen-Vacancy (NV) centers, have attracted attention as alternative DNP agents because they can potentially be optically hyperpolarized at room temperature. Here, unraveling new physics underlying an optical DNP mechanism first introduced by Ajoy et al. [Sci. Adv. 4, eaar5492 (2018)], we report the realization of a miniature "optical nanodiamond hyperpolarizer," where C nuclei within the diamond particles are hyperpolarized via the NV centers. The device occupies a compact footprint and operates at room temperature. Instrumental requirements are very modest: low polarizing fields, low optical and microwave irradiation powers, and convenient frequency ranges that enable miniaturization. We obtain the best reported optical C hyperpolarization in diamond particles exceeding 720 times of the thermal 7 T value (0.86% bulk polarization), corresponding to a ten-million-fold gain in averaging time to detect them by NMR. In addition, the hyperpolarization signal can be background-suppressed by over two-orders of magnitude, retained for multiple-minute long periods at low fields, and deployed efficiently even to C enriched particles. Besides applications in quantum sensing and bright-contrast MRI imaging, this work opens possibilities for low-cost room-temperature DNP platforms that relay the C polarization to liquids in contact with the high surface-area particles.
动态核极化（DNP）是一套强大的技术，可在核磁共振（NMR）和磁共振成像（MRI）中实现信号增强数倍。所产生的非热自旋态还可用于量子传感以及作为多体物理的探针。典型的DNP方法需要使用低温冷却剂、强磁场和高功率微波激发，这些既昂贵又不便于使用。富含氮空位（NV）中心的纳米金刚石颗粒作为替代的DNP试剂引起了关注，因为它们有可能在室温下被光学超极化。在此，通过揭示Ajoy等人[《科学进展》4，eaar5492（2018）]首次提出的光学DNP机制背后的新物理原理，我们报告了一种微型“光学纳米金刚石超极化器”的实现，其中金刚石颗粒内的碳原子核通过NV中心被超极化。该装置占地面积小，且在室温下运行。仪器要求非常适度：低极化场、低光学和微波辐照功率以及便于实现小型化的合适频率范围。我们在金刚石颗粒中获得了目前报道的最佳光学碳超极化，超过热平衡7T值的720倍（体极化率为0.86%），这相当于通过NMR检测它们的平均时间增益了一千万倍。此外，超极化信号的背景可被抑制两个数量级以上，在低场下可保持数分钟，甚至能有效地应用于富含碳的颗粒。除了在量子传感和亮对比度MRI成像中的应用外，这项工作还为低成本室温DNP平台开辟了可能性，该平台可将碳极化传递给与高表面积颗粒接触的液体。
