Orientation independent room-temperature optical 13C hyperpolarization in powdered diamond

TL;DR

This paper presents a room-temperature, orientation-independent method for hyperpolarizing 13C nuclei in powdered diamond using optical and microwave techniques, enabling enhanced NMR sensitivity without requiring crystal alignment.

Contribution

The authors develop a novel approach combining optical illumination and broad microwave sweeps to hyperpolarize diamond powder regardless of crystal orientation.

Findings

Achieved over 0.25% bulk 13C polarization at room temperature.

Demonstrated orientation-independent hyperpolarization in powdered diamond.

Potential applications in biosensing and liquid spin hyperpolarization.

Abstract

Dynamic nuclear polarization via contact with electronic spins has emerged as an attractive route to enhance the sensitivity of nuclear magnetic resonance (NMR) beyond the traditional limits imposed by magnetic field strength and temperature. Among the various alternative implementations, the use of nitrogen vacancy (NV) centers in diamond - a paramagnetic point defect whose spin can be optically polarized at room temperature - has attracted widespread attention, but applications have been hampered by the need to align the NV axis with the external magnetic field. Here we overcome this hurdle through the combined use of continuous optical illumination and a microwave sweep over a broad frequency range. As a proof of principle, we demonstrate our approach using powdered diamond where we attain bulk 13C spin polarization in excess of 0.25 percent under ambient conditions. Remarkably, our technique acts efficiently on diamond crystals of all orientations, and polarizes nuclear spins with a sign that depends exclusively on the direction of the microwave sweep. Our work paves the way towards the use of hyperpolarized diamond particles as imaging contrast agents for biosensing and, ultimately, for the hyperpolarization of nuclear spins in arbitrary liquids brought in contact with their surface.