基于金刚石氮-空位(NV)色心的温度传感技术, 通过测量其基态子级之间的零场劈裂值(D)来实现对温度的感测。 由于金刚石稳定性高, 抗干扰能力强, 可制成不同尺寸, NV色心测温方法被视为解决微纳米尺度温度高精度测量难题的一种重要技术途径, 具有良好的应用前景。 实验测量中, 首先使用激光对色心进行电子自旋极化, 然后使用微波对电子自旋进行调控, 进而探测电子跃迁发出的荧光得到光学探测磁共振(ODMR)光谱, 对谱线进行拟合分析获得D值。 激光功率波动是重要的实验噪声来源之一, 为了获得较高的极化率, 需要足够的激光功率, 然而较大激光功率下, 光功率波动会影响电子自旋极化率, 从而降低电子跃迁所发出荧光强度的稳定性, 增加光谱的噪声, 最终增大数据测量的误差。 在常规测量中, 不使用任何归一化参考的直接拟合法会将激光功率的波动直接反映在ODMR光谱上。 为降低激光功率波动产生的误差, 提出了一种特定编码的脉冲序列测量方法, 可以在实验过程中获得不受微波调控的光子数参考值, 对所探测的受到微波调控的光子数相对于参考值做归一化, 从而输出归一化光谱。 在实验室搭建的ODMR测量系统上开展了控温300 K的对比实验, 考虑对脉冲编码序列两个时间参数的优化, 确定了0.8 s的计数时间和0.001 s的准备时间。 在不同的激光功率下, 分别采用直接拟合法、 数学归一化法和脉冲编码归一化法测得三组D值。 数据分析结果表明, 相较于直接拟合法和数学归一化法, 脉冲编码归一化法将激光功率波动引入的噪声有效地抑制到了直接拟合法的62.5%, 得到D值的误差从直接拟合法的179 kHz和数学归一化法的165 kHz减小到了56.9 kHz。 该方法可为金刚石NV色心测温技术提供一种抑制激发激光功率影响的有效途径, 提高D值测量分辨力, 为金刚石NV色心测温技术的实用化发展奠定基础。

Thermometry based on nitrogen-vacancy (NV) center in diamond realizes temperature sensing by measuring the zero-field splitting parameter (D) between the sublevels of its ground state. Since diamond has high stability, the resistance to interference, and can be processed into different sizes, thermometry is regarded as a feasible solution to high-precision temperature measurement on the micro-nano scale, which has the potential to be developed into practical application. In the measurement of D, the laser is applied to excite spin polarization and a microwave is then used to manipulate the electron spin. The optically detected magnetic resonance (ODMR) spectrum is obtained by detecting fluorescence released in the transition of the electrons, and the spectral lines are fitted to determine the values of D. Fluctuation of laser power is one of the important sources of experimental noise. To realize a high probability of spin polarization applying laser with high power is necessary. However, the fluctuation at a relatively high laser power will influence the probability of spin polarization, decrease the stability of the fluorescence intensity detected, and increase the error of data. The traditional method, which outputs the photon count rate directly without any reference for normalization, will reflect the fluctuation of laser power in the spectrum. This paper proposes a method to reduce the laser-induced error, in which a reference value of photon count without effective manipulation of microwave can be measured at each count using a specifically-encoded pulse sequence, and normalized fluorescence intensity will be obtained in the spectrum after normalizing the photon count under the manipulation of microwave to the reference. In this way, the effect of the laser power fluctuation on the spectrum will be weakened. The comparative experiments were carried out at 300 K on the ODMR measurement system built in the laboratory. A count time of 0.8 s and a preparation time of 0.001 s were determined considering the optimization of the two time-related parameters. Under different laser powers, three groups of D values were measured by the direct fitting, mathematical, and pulse code normalization methods. The experimental results demonstrate that using pulse code to obtain reference for normalization can effectively suppress laser-induced error to 62.5% of that without any reference, and improve the data accuracy from 179 kHz with no reference and 165 kHz with mathematical reference to 56.9 kHz by comparison. The method can effectively suppress the laser-induced error, improve the resolution of the determination of D, and lay a foundation for the practical development of thermometry based on NV centers.