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图 3a中描绘了实验过程中在不同激发条件下所收集到的典型光谱。其中仅在抽运光(信号光)作用下收集到的自发辐射光信号光强Ip(Is)用橙色(红色)实线的曲线表示,而蓝色虚线的曲线则表示抽运光和信号光共同作用下收集的既含有自发辐射光又含有受激辐射光同时还有入射光的信号光强Is, p。可以用增益系数α来表征其放大的特性:
$ \alpha=\frac{I_{\mathrm{s}, \mathrm{p}}(637)-I_{\mathrm{s}}(637)-I_{\mathrm{p}}(637)}{I_{\mathrm{s}}(637)} \times 100 \% $
(1) 式中,Ip(637), Is(637)和Is, p(637)分别表示上述3种不同激发条件下收集到的波长在637nm处的信号。在图 3a中它们的值分别为0.14,0.71和0.91,因而其增益系数的值为8.5%。而图 3b中则是通过金刚石侧面的光纤光谱仪监测到的荧光衰弱信号Id:
$ I_{\mathrm{d}}=I_{\mathrm{s}, \mathrm{p}}^{\prime}-I_{\mathrm{s}}^{\prime}-I_{\mathrm{p}}^{\prime} $
(2) 式中,Is′, Ip′和Is, p′分别表示在仅有抽运光、仅有信号光、以及抽运光和信号光同时激发金刚石这3种情况下光纤光谱仪所接收到的光强。可以看出,NV色心在信号光的作用下,其自发辐射荧光的强度降低了。因为处于NV色心激发态的粒子有一部分在信号光的作用下通过受激辐射返回到基态,因而抑制了发生自发辐射跃迁的概率,从而自发辐射荧光强度发生衰减。观察到荧光衰减的现象从侧面也反映出NV色心在信号光的作用下产生了受激辐射。此外,荧光衰减信号在637nm处观察到了一个微弱的尖峰,这应该归因于信号光有小部分散射到光纤光谱仪的方向,因而也收集到了部分受激辐射的信号。
为了尽可能地提高增益系数,首先通过旋转HWP1和HWP2来改变抽运光和信号光的偏振角度θp和θs,探究受激辐射的偏振特性对增益系数的影响,并且作者将抽运光在固定功率下激发NV色心得到荧光强度最强时的抽运光偏振方向定义为0°,而增益系数受到光的偏振角度影响可以用偏振对比度P表征:
$ P=\frac{\alpha_{\max }-\alpha_{\min }}{\alpha_{\max }+\alpha_{\min }} \times 100 \% $
(3) 在实验过程中,首先将抽运光和信号光的功率分别固定在1.25W和2.00μW,然后固定HWP2的角度,随后逐步旋转HWP1并记录每次旋转后增益系数的大小,探究增益系数与θp的关系(见图 4a),得到偏振对比度为10.2%;接着固定HWP1,再通过旋转HWP2得到增益系数与θs的关系(见图 4b),得到偏振对比度为6.9%。可以看出,增益系数会因抽运光和信号光偏振方向的改变而发生变化。这是因为沿(100)面生长的金刚石中NV色心只能有[111], [111], [111]和[111]晶向这几个固定的取向,其吸收截面和发射截面都会受到光偏振方向的影响,从而影响放大的特性。
在将抽运光和信号光的角度调整到最佳位置后,作者对增益系数与抽运光功率Pp和信号光功率Ps之间的关系展开了研究。在1.00μW~5.50μW范围内调节信号光功率,并在0.39W~2.51W的范围来调节抽运光功率优化增益系数。图 5a是增益系数受抽运光功率和信号光功率影响的等值线图。其中横坐标表示抽运光功率的大小,纵坐标表示信号光功率的大小,而旁边的颜色标尺指出了图中不同颜色所对应的增益系数的大小。图 5b中描绘了信号光为2.00μW时,增益和抽运光的关系。从图中可以很直观地看出,增益系数随抽运光功率增加而增加,这与之前初步调查的结果是一致的; 而信号光则在2.00μW左右增益系数有最大值,并在抽运光最大时(2.51W)得到了10.5%的增益系数,且呈现出增益饱和趋势。作者用一条功率饱和曲线对图 5b中的数据进行了拟合:
$ \alpha\left(P_{\mathrm{p}}\right)=\frac{\alpha_{\infty} \times P_{\mathrm{p}}}{P_{\mathrm{p}}+P_{\mathrm{sat}}} $
(4) 式中,α∞是抽运光功率为无穷大时的饱和增益系数,Psat是饱和抽运功率。从拟合曲线中能得出α∞和Psat的值分别为11.4%±0.4%和0.32W±0.06W,因此,理论上目前这套系统的增益系数极限可以达到11.4%。
金刚石氮-空位色心零声子线的受激辐射放大
Amplification of stimulated radiation on the zero-phonon line of nitrogen-vacancy color centers in diamond
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摘要: 为了解决在基于金刚石氮-空位(NV)色心的磁场高灵敏度测量中,高速获取磁场信号引起的NV色心发光强度的微小变化的技术瓶颈问题,自行设计出一套能够实现金刚石NV色心自发辐射和受激辐射信号同步测量的光学系统,并利用一个长焦距透镜收集金刚石NV色心受激辐射信号,从而尽最大可能地滤除金刚石NV色心的自发辐射信号,提高测量受激放大增益的信噪比。实验中成功观察到NV色心零声子线的受激辐射放大,分析了抽运光功率、信号光功率、抽运光偏振方向和信号光偏振方向对放大特性的影响。结果表明,通过对抽运光和信号光相关参量的优化调整,最终获得了10.5%的受激辐射增益。该研究为实现NV光放大远程磁场监测奠定了研究基础。Abstract: In order to solve the technical bottleneck of the sensitive detection of the optically detected magnetic resonance (ODMR) signal from the nitrogen vacancy (NV) color centers in the diamond by taking the advantage of the directional amplification of stimulated radiation, an optical amplification system was set up to investigate the stimulated radiation of NV color centers in diamond, where the maximum amplification efficiency reached 10.5%. Besides, it is found that the amplification efficiency is related to the pump laser power and signal laser power as well as the polarization states of the two lasers. The results show that it is promising to use the amplification of stimulated radiation to replace the fluorescence in the ODMR measurement with NV color centers in the application of remote sensing.
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[1] KITCHING J. Chip-scale atomic devices[J]. Applied Physics Review, 2018, 5(3): 031302. doi: 10.1063/1.5026238 [2] TANG J J, ZHAI Y Y, CAO L, et al. High-sensitivity operation of a single-beam atomic magnetometer for three-axis magnetic field mea-surement[J]. Optics Express, 2021, 29(10): 15641-15652. doi: 10.1364/OE.425851 [3] HUANG Sh, ZHANG W, XI Q, et al. Fabrication imperfection effect on Si/SiO2-InP micropillar cavities for 1.55μm single photon source[J]. Laser Technology, 2020, 44(5): 532-537(in Chinese) [4] CHEN Y C, GRIFFITHS B, WENG L, et al. Laser writing of individual nitrogen-vacancy defects in diamond with near-unity yield[J]. Optica, 2019, 6(5): 662-667. doi: 10.1364/OPTICA.6.000662 [5] RONG Y Y, JU Zh P, MA Q, et al. Efficient generation of nitrogen vacancy centers by laser writing close to the diamond surface with a layer of silicon nanoballs[J]. New Journal of Physics, 2020, 22(1): 013006. doi: 10.1088/1367-2630/ab6351 [6] JU Zh P, LIN J J, SHEN S, et al. Preparations and applications of single color centers in diamond[J]. Advances in Physics, 2021, X6(1): 1858721. [7] BARRY J F, SCHLOSS J M, BAUCH E, et al. Sensitivity optimization for NV-diamond magnetometry[J]. Reviews of Modern Physics, 2020, 92(1): 015004. doi: 10.1103/RevModPhys.92.015004 [8] THIEL L, WANG Z, TSCHUDIN M A, et al. Probing magnetism in 2D materials at the nanoscale with single-spin microscopy[J]. Science, 2019, 364(6444): 973-976. doi: 10.1126/science.aav6926 [9] XAVIER J, YU D Sh, JONES C, et al. Quantum nanophotonic and nanoplasmonic sensing: towards quantum optical bioscience laboratories on chip[J]. Nanophotonics, 2021, 10(5): 1387-1435. doi: 10.1515/nanoph-2020-0593 [10] TIMO W, CHRISTIAN G, FLORIAN F, et al. Determination of the three-dimensional magnetic field vector orientation with nitrogen vacany centers in diamond[J]. Nano Letters, 2020, 20(5): 2980-2985. doi: 10.1021/acs.nanolett.9b04725 [11] BIAN K, ZHENG W T, ZHENG X Zh, et al. Nanoscale electric-field imaging based on a quantum sensor and its charge-state control under ambient condition[J]. Nature Communications, 2021, 12(1): 2457. doi: 10.1038/s41467-021-22709-9 [12] SMITH J M, MEYNELL S A, JAYICH A C B, et al. Colour centre generation in diamond for quantum technologies[J]. Nanophotonics, 2019, 8(11): 1889-1906. doi: 10.1515/nanoph-2019-0196 [13] MURZIN D, MAPPS D J, LEVADA K, et al. Ultrasensitive magnetic field sensors for biomedical applications[J]. Sensors, 2020, 20(6): 1569. doi: 10.3390/s20061569 [14] CASOLA F, VAN DER SAR T, YACOBY A. Probing condensed matter physics with magnetometry based on nitrogen-vacancy centres in diamond[J]. Nature Reviews Materials, 2018, 3(1): 17088. doi: 10.1038/natrevmats.2017.88 [15] ASHFOLD M N R, GOSS J P, GREEN B L, et al. Nitrogen in diamond[J]. Chemical Reviews, 2020, 120(12): 5745-5794. doi: 10.1021/acs.chemrev.9b00518 [16] SUBEDI S D, FEDOROV V V, PEPPERS J, et al. Laser spectroscopic characterization of negatively charged nitrogen-vacancy (NV-) centers in diamond[J]. Optical Materials Express, 2019, 9(5): 2076-2087. doi: 10.1364/OME.9.002076 [17] FRACZEK E, SAVITSKI V G, DALE M, et al. Laser spectroscopy of NV- and NV0 colour centres in synthetic diamond[J]. Optical Materials Express, 2017, 7(7): 2571-2585. doi: 10.1364/OME.7.002571 [18] JESKE J, LAU D W, VIDAL X, et al. Stimulated emission from nitrogen-vacancy centres in diamond[J]. Nature Communications, 2017, 8: 14000. doi: 10.1038/ncomms14000 [19] NAIR S R, ROGERS L J, VIDAL X, et al. Amplification by stimulated emission of nitrogen-vacancy centres in a diamond-loaded fibre cavity[J]. Nanophotonics, 2020, 9(15): 4505-4518. doi: 10.1515/nanoph-2020-0305 [20] ZHAO X, DONG J, GAO W, et al. Progresses of surface enhanced fluorescence[J]. Laser Technology, 2018, 42(4): 511-520(in Chinese). [21] ARDAKANI S B, FAEZ R. Tunable spherical graphene surface plasmon amplification by stimulated emission of radiation[J]. Journal of Nanophotonics, 2019, 13(2): 026009.