Relaxometry schemes employing nitrogen-vacancy (NV) centers in diamonds are essential in biology and physics to detect a reduction of the color centers' characteristic spin relaxation ($T_1$) time caused by, e.g., paramagnetic molecules in proximity. However, while only the negatively-charged NV center is to be probed in these pulsed-laser measurements, an inevitable consequence of the laser excitation is the conversion to the neutrally-charged NV state, interfering with the result for the negatively-charged NV centers' $T_1$ time or even dominating the response signal. In this work, we perform relaxometry measurements on an NV ensemble in nanodiamond combining a $520\,$nm excitation laser and microwave excitation while simultaneously recording the fluorescence signals of both charge states via independent beam paths. Correlating the fluorescence intensity ratios to the fluorescence spectra at each laser power, we monitor the ratios of both charge states during the $T_1$-time measurement and systematically disclose the excitation-power-dependent charge conversion. Even at laser intensities below saturation, we observe charge conversion, while at higher intensities, charge conversion outweighs spin relaxation. These results underline the necessity of low excitation power and fluorescence normalization before the relaxation time to accurately determine the $T_1$ time and characterize paramagnetic species close to the sensing diamond.
Quantum relaxometry for detecting biomolecular interactions with single NV centers
University of Science and Technology of China（中国科学技术大学）；Anhui Province Key Laboratory of Scientific Instrument Development and Application, University of Science and Technology of China（中国科学技术大学安徽省科学仪器开发与应用重点实验室）；School of Biomedical Engineering and Suzhou Institute for Advanced Research, University of Science and Technology of China（中国科学技术大学生物医学工程学院苏州高等研究院）；Zhejiang University（浙江大学）；Nanjing University（南京大学）；Nankai University（南开大学）；Hefei National Laboratory, University of Science and Technology of China（中国科学技术大学合肥国家实验室）；Hefei National Research Center for Physical Sciences at the Microscale, Department of Polymer Science and Engineering, University of Science and Technology of China（中国科学技术大学高分子科学与工程系微尺度物质科学国家研究中心）
Removing inhomogeneous broadening in cross-relaxation spectra via hole burning
University of Science and Technology of China（中国科学技术大学）；Hefei National Research Center for Physical Sciences at the Microscale（合肥微尺度物质科学国家研究中心）；Hefei National Laboratory（合肥国家实验室）
Quantum Relaxometry Under Continuous Wave Excitation
HUN-REN Wigner Research Centre for Physics（匈牙利科学院维格纳物理研究中心）；György Hevesy Doctoral School, Institute of Chemistry, ELTE Eötvös Loránd University（ELTE厄特沃什·罗兰大学化学研究所乔治·海切伊博士学院）；Department, Voevodsky Institute of Chemical Kinetics and Combustion SB RAS（俄罗斯科学院西伯利亚分院沃耶沃德斯基化学动力学与燃烧研究所系）；Budapest University of Technology and Economics（布达佩斯技术与经济大学）；MTA-WFK Lendület “Momentum” Semiconductor Nanostructures Research Group（匈牙利科学院-维格纳物理中心Lendulet“动量”半导体纳米结构研究组）
