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面对宽幅地形测绘和空基大气测量等应用的需求, 迫切需要发展能够适应机载平台的低功耗的小型化单光子探测系统. 超导纳米线单光子探测器(SNSPD)因性能优异, 已被应用到量子信息、深空通信和远程激光雷达等领域. 然而, 常规SNSPD所需低温系统的体积和重量均较大, 不易于应用到机载平台. 截至目前, 国际上还未出现应用于机载平台的SNSPD的相关报道. 本文设计并制备了工作温度为4.2 K的SNSPD. 超导探测器芯片是光敏面积为60 μm × 60 μm的四通道光子数可分辨器件, 通过光束压缩系统耦合到直径200 μm的光纤, 在温度为4.2 K时量子效率大于50%@1064 nm. 最后, 测试了单个通道的时间特性, 在不同光子数响应的情况下得到了不同的时间抖动, 其中四光子响应时的时间抖动最小, 半高宽为110 ps. 该工作不仅可支撑机载应用, 而且对于推动发展通用的小型化SNSPD系统及其应用具有积极意义.
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关键词:
- 超导纳米线单光子探测器 /
- 液氦温区 /
- 光子数分辨 /
- 机载平台
Facing the demand for applications such as wide-area terrain mapping and space-based atmospheric measurements, there is an urgent need to develop miniaturized single-photon detection systems with low power consumption that can be adapted to airborne platforms. Superconducting nanowire single-photon detectors (SNSPDs) have been applied to quantum information, bioimaging, deep space communication and long-range lidar with the advantages of high quantum efficiency, low dark count rate and fast detection rate. However, traditional SNSPD usually operates at 2.1 K or even lower, and the required cryogenic systems are large in size and weight, which are not easy to apply to airborne platforms. Up to now, there has been no report on SNSPD applied to airborne platforms. How to apply SNSPD to airborne platforms is an urgent problem to be solved. In this work, we design and make an SNSPD with an operating temperature of 4.2 K. The superconducting detector chip is a four-channel photon-number-resolving device with a photosensitive area of 60 μm × 60 μm, which is coupled to a 200-μm-diameter fiber by a beam compression system with a quantum efficiency of 50% at 1064 nm and a temperature of 4.2 K. Finally, the time characteristics of a single channel are tested in response to different photon numbers. The timing jitter of four-photon response is smallest, and the half-height width is 110 ps. This work not only supports airborne applications, but also has positive implications for promoting the development of general-purpose miniaturized SNSPD systems and their applications. 1. 引 言
近年来, 单光子探测技术凭借着极高的单光子灵敏度和皮秒量级时间分辨率的优势, 打破了传统激光雷达只能通过增大激光功率和增大望远镜口径来提高探测系统信噪比的技术禁锢, 为激光雷达带来了突破性进展. 单光子激光雷达在目标探测、大气测量和地形测绘等应用中发挥了重要作用, 其中面向宽幅地形测绘和空基大气测量等应用的机载平台激光雷达需要小型化的单光子探测器. 目前, 常用工作在盖革模式下的雪崩光电二极管探测器(Geiger-mode avalanche photodiode, GM-APD)[1,2]取代传统工作在线性模式的光电二极管探测器, 极大地提高了系统的探测灵敏度, 其在微弱信号探测领域具有明显优势. 然而, GM-APD只能通过响应区分光子的有无, 而无法区分光子数量, 即无法辨别信号强弱. 为实现光子数探测, 研究人员通常采用多周期累加技术[3]进行目标识别和探测, 导致建立统计直方图所需时间周期较长. 超导纳米线单光子探测器(superconducting nanowire single photon detectors, SNSPD)[4-8]具有探测效率高、时间精度高、探测速度快和暗计数率低等特点, 且通过探测器结构设计后具备光子数分辨的能力[9-12], 目前已广泛应用于量子通信[13]、激光雷达[14]、荧光寿命成像[15], 以及与纳米光子电路的芯片集成[16].
国际上已经开发并设计出了小型平台应用的低功耗和紧凑型闭环冷却低温恒温器, 技术支撑大致分为液氦杜瓦和机械式制冷, 所达基础温度约为4.0 K. 根据大气环境温度与海拔高度的关系[17], 机载设备飞行高度在10—20 km之间, 对应大气压从31000 Pa降至9000 Pa. 液氦在常压下的温度为4.2 K, 且随着大气压的减小液氦的温度可以降至更低[18], 在大气压从31000 Pa降至9000 Pa的过程中, 液氦温度可以降至3 K以下. SNSPD常用的超导材料主要有NbN, NbTiN, MoSi[19,20], YBCO[21]和MgB2[22]等. 目前国内外报道液氦温区SNSPD的相关结果如表1所列, 其中, NbN和NbTiN具备较高的超导转变温度, 较窄的超导转变宽度, 良好的热稳定性和导热性, 因而被广泛应用于超导探测器. MoSi的超导能隙更低, 探测灵敏度更高, 尤其在中远红外波段, MoSi器件有很大的优势, 但其需工作在较低温度. YBCO和MgB2有更高的超导转变温度, 但其薄膜质量受制备工艺限制, 目前尚未有较好的探测效果. 对于宽幅地形测绘和空基大气测量等应用, 通过匹配大口径的光学系统可以提高光耦合和探测回波光子的效率, 因此使用的探测器需要具备大光敏面面积.
表 1 液氦温区SNSPD国内外研究进展Table 1. Progress of domestic and international research on SNSPD in liquid helium temperature region.针对机载环境及探测需求, 迫切需要开发工作在液氦温区的大光敏面SNSPD. 根据Ginzburg-Landau理论, 由公式
Ic∝[1−(T/Tc)2]3/2 可知SNSPD的超导转变电流(Ic)随温度(T)的升高而降低, 进而导致探测效率下降. 针对此问题, 一种解决方法为提高超导薄膜的超导转变温度(Tc); 另一种即采用窄线宽纳米线方式, 使SNSPD具有较长的饱和量子效率区间[27,28].2. 器件制备
本文制备的探测器芯片以NbN作为超导材料, NbN薄膜厚度为7 nm, 制备流程如图1所示. 芯片设计为四通道阵列结构, 总面积为60 μm × 60 μm, 单个通道由4个面积为15 μm × 15 μm的像元串联组成, 共计16像元. 探测器芯片采用串联纳米线并联电阻方式实现光子数分辨, 每个纳米线像元采用传统SNSPD的蜿蜒结构, 并在纳米线两端并联一个电阻Rp. 当一个纳米线像元吸收光子时, 破坏其局部超导性, 在纳米线截面上产生千欧姆量级的电阻区域Rn(t). 如果Rp的值远小于Rn(t), 则偏置电流被转移到并联电阻中, 并产生电压脉冲. 当更多的光子被不同像元吸收, 偏置电流流入相应的并联电阻(多个电阻Rp串联), 所有这些电阻上产生的电压在输出端叠加, 产生一个幅值与吸收光子数量成正比的脉冲[11]. 实验表明, 在不同的入射光功率下, 该结构共可实现16个光子的分辨.
探测器芯片制备过程主要包括以下7个步骤. 1)采用等离子体增强化学的气相沉积(PECVD)方法在Si衬底上沉积134 nm厚的Si3N4层. 2)薄膜制备: 采用磁控溅射在Si3N4上制备NbN薄膜(工艺参数Ar:N2 = 70 sccm∶10 sccm (1 sccm = 1 mL/min), 气压2 mTorr (1 mTorr = 0.133 Pa), 溅射电流1.05 A). 通过透射电子显微镜和原子力显微镜测得NbN薄膜的厚度为 7 nm, 平均粗糙度为 0.14 nm. 经测试得7 nm厚度NbN的Tc约为8.2 K, 方阻Rsq = 271 Ω/square. 3)电极制备: 采用紫外光刻法制备Au电极. 4)纳米线制备: 采用聚甲基丙烯酸甲酯(PMMA)电子束光刻胶, 通过电子束曝光(EBL)和反应离子刻蚀(RIE)制备纳米线条, 如图2所示, 线宽为65 nm ± 2 nm, 分布较为均匀. 刻蚀条件: 刻蚀气体SF6/CHF3参数为20/40 sccm, 工作压强4 Pa, 刻蚀功率80 W, 刻蚀时间30 s. 5)并联电阻Rp制备: 通过EBL和显影后得到并联电阻图案, 再利用磁控溅射生长钛(Ti)作为并联电阻材料, 制备的并联电阻Rp = 50 Ω. 6)光学腔制备: 利用PECVD在纳米线上方生长180 nm厚的SiO2层作为SiO2光学腔, 此方法可以增加纳米线的光学吸收率[29]. 7)反射镜制备: 在SiO2光学腔上方制备一层Au反射镜, 以减小透射光损耗. 首先利用EBL在纳米线区域制备反射镜图案, 后用磁控溅射生长100 nm厚的Au层, 并剥离出Au反射镜.
图 2 纳米线扫描电子显微镜图: 总面积为60 μm × 60 μm, 共四个通道, 每个通道包括4个像元(①②③④). 红色圆虚线表示入射光斑大小, 直径为60 μm. 绿色线框表示1号通道左、中、右3个位置处的纳米线, 线宽为65 nm ± 2 nm, 分布较为均匀Fig. 2. Scanning electron microscopy of nanowires: total area is 60 μm × 60 μm, four channels, each channel includes four pixels (①②③④). The red dotted line is the size of the incident light spot, with a diameter of 60 μm. The green line frame is the nanowire at the left, middle and right of Channel 1, with a line width of 65 nm ± 2 nm and relatively uniform distribution.3. 器件性能表征
本文实验采用1064 nm脉冲激光器作为光源, 使用可调衰减器衰减入射光功率以获得单光子信号. 从芯径为200 μm的光纤末端输出的单光子信号还需经过放大倍率为0.3倍的光学透镜组聚焦后穿过厚度为500 μm的 Si衬底耦合至探测器光敏面. 入射光经耦合透镜组聚焦至探测器上的光斑直径为60 μm, 略小于探测器芯片的光敏面积. 其中, 厚度为500 μm的Si衬底对1064 nm波段光的透过率为61%. 将探测器安装在可控温的GM(Gifford-Mcmahon)制冷机中, 最低工作温度可达2.1 K. 电流-电压(I-V)特性体现了SNSPD最基本的超导特性, 决定了探测器的正常工作范围, 偏置电流(Ib, 提供给探测器的电流, 最大值受超导临界电流限制)的大小直接影响探测器的探测效率、暗计数率和脉冲幅度等基本特性. 探测效率是SNSPD最主要的特性之一, 通过对GM制冷机进行控温, 分别测量在3.0, 3.5, 4.2 K 这3个温度下器件的系统效率和量子效率. 综合考虑探测系统中光路的耦合与连接等导致光损耗的因素, 系统效率ηsystem具体表示为: ηsystem = ηcouplingηabsorptionηquantum, 其中, ηquantum表示量子效率, ηabsorption表示纳米线吸收入射到纳米线表面的光子的效率, ηcoupling表示光耦合效率. 本文实验结果表明, 在暗计数率为1000 counts/s时, 3.0, 3.5 K温度下的系统效率分别为47%, 46%.
量子效率如图3(a)所示, 随着温度的上升, Ic有所下降, 但在3.0, 3.5 K温度下4个通道的ηquantum 均达饱和, 即ηquantum接近于1. 当温度升至4.2 K时, 量子效率未达到饱和. 根据Fano涨落理论, ηquantum与偏置电流Ib的关系为[30]: ηquantum
=12erfc(Ic0−IbΔI) . 其中, Ic0为RPCR/RPCRsaturation = 0.5时所对应的偏置电流, RPCR为光子计数率, RPCRsaturation为饱和光子计数率; ηquantum在偏置电流上的转变宽度ΔI可计算为: ΔI = Ib (ηquantum = 80%) – Ib (ηquantum = 20%). 图3(a)中橙色系列实线表示对实验结果的拟合, 实验结果表明在温度为4.2 K时4个通道的量子效率均大于50%. 从图3(a)可看出4个通道的结果一致性不足, 主要是偏置电流大小不一致. 超导临界电流的大小受到纳米线区域中最小线宽影响, 而纳米线线宽的均匀性主要受纳米线制备工艺方面影响. 对于整个纳米线区域, 4个通道中任意位置处的纳米线线宽不一致, 则超导临界电流不一致, 导致偏置电流(Ib)也不一致. 同时也可能受到耦合光斑位置的影响, 这里制备的探测器光敏面略大于耦合光斑大小, 但是耦合光斑中心位置可能略有偏差, 作为一个整体, 对系统效率等指标影响很小.
图 3 器件性能测试 (a) 器件在不同温度下的量子效率, 在温度小于3.5 K时四通道量子效率均达饱和, 但饱和区间长度随着温度上升而减小, 当温度升至4.2 K时, 通过对实验结果的拟合, 得到4个通道的量子效率均大于50%; (b) 光子响应幅值分布统计, 呈现4个高斯分布, 统计分布的中心值分别为56 , 72, 87, 98 mV, 分别对应单光子、双光子、三光子和四光子响应情况; (c) 通过示波器采集不同光子数响应的脉冲信号, 单光子响应时的信噪比为56 mV/20 mV ≈ 2.8Fig. 3. Device performance test: (a) Quantum efficiency test of the device at different temperatures. The quantum efficiency of all four channels saturates at temperatures less than 3.5 K, but the length of the saturation interval decreases as the temperature rises. When the temperature rises to 4.2 K, the quantum efficiency of the four channels is obtained by fitting the experimental results, which is greater than 50%; (b) the statistics of photon response amplitude distribution, showing four Gaussian distributions with the center values of statistical distributions of 56 , 72 , 87 and 98 mV, corresponding to the single-photon, two-photon, three-photon and four-photon response cases, respectively; (c) the acquisition of different photon number response by oscilloscope, and the signal-to-noise ratio of single photon response is 56 mV/20 mV ≈ 2.8.本文利用示波器统计响应信号幅值的分布, 设置鉴别电平为高于噪声幅值的30 mV. 控制制冷机温度为4.2 K, 将1通道的偏置电流设置为7.5 μA进行测试. 利用常温放大器提供50 dB增益, 并调节入射光功率使探测器工作在多光子响应模式. 图3(b)展示了示波器采集的信号幅值的分布, 共采集了3万次左右的光子响应计数, 此统计图呈现出4个高斯分布, 分别对应单光子、双光子、三光子和四光子响应情况, 幅值分布的中心值分别为56, 72, 87和98 mV. 本文制备了四通道并行读出的阵列光子数分辨SNSPD, 单个通道实现了4个光子数分辨, 4个通道可实现16个光子数分辨. 利用示波器采集不同光子数响应的脉冲信号波形, 脉冲恢复时间(t)半高宽为90 ns, 单光子响应时的信噪比为56 mV/20 mV ≈ 2.8, 如图3(c)所示.
时间抖动描述了光子到达探测器的时间与输出脉冲时间之间的波动. 将飞秒激光器输出光源经分束器分成两路: 一路经过衰减器后作为SNSPD的输入光信号, 另外一路接入高速示波器作为参考时间信号. 测量SNSPD响应信号和参考信号之间的时间延迟Δt并统计时间抖动值. 本文实验测量了其中一个通道的时间抖动, 将入射光衰减至单光子水平, 以保证每个光脉冲的到来只有一个像元响应. 该器件单个通道由4个像元串联组成, 因此测量时间抖动时, 不同像元之间信号传输线长度不同, 导致信号传输时间不同, 在时间轴上即表现为4个高斯分布, 拟合得到每个高斯分布的半高宽均在200 ps左右, 如图4(a)所示. 同时, 由于传输电缆长度的差异, 各像元的信号输出时间略有差异, 大约在百皮秒量级. 在实际使用中, 这个差异可以通过更换不同长度电缆, 或者增加延迟电路等措施克服. 在多光子响应模式, 由于存在双光子、三光子和四光子响应多种状态, 在时间轴上无明显的分布特征, 如图4(b)所示. 由于图4(a)和图4(b)的幅值分布都存在交叠, 无法得到一个准确的抖动值. 提高示波器触发电平, 只统计四光子响应的脉冲信号, 如图4(c)所示, 故只存在一个高斯分布. 四光子响应时的幅值最高, 所以信噪比较高, 有利于降低时间抖动, 这与实测的110 ps抖动一致.
图 4 时间特性测试 (a) 单光子响应模式下时间抖动测量; 由于器件单通道包含了4个像元, 不同像元之间信号传输线的长度不同, 导致信号传输时间不同, 在时间轴上表现为4个高斯分布的叠加; (b) 多光子响应时时间抖动测量; 由于存在双光子、三光子和四光子响应多种状态, 在时间轴上无明显的分布特征; (c) 四光子响应时间抖动测量; 只存在4个像元同时响应的情况, 因此只有一个高斯分布, 此时抖动最小, 高斯分布半高宽110 psFig. 4. Time characteristic test: (a) Timing jitter measurement in single-photon response mode. Because the single channel of the device contains four pixels, the length of signal transmission lines between different pixels is different, resulting in different signal transmission time, which is shown as the superposition of four Gaussian distributions on the time axis. (b) Measurement of timing jitter in multi-photon response. Due to the existence of two-photon, three-photon and four-photon response states, there is no obvious distribution characteristics on the time axis. (c) Four-photon response timing jitter measurement. Only four pixels respond at the same time, so there is only one Gaussian distribution. At this time, the jitter is minimum, and the half-height width of the Gaussian distribution is 110 ps.为了应对机载测试中的发射加速、剧烈振动和冲击等机械环境的考验, 设计了抗冲击和振动的超导芯片封装系统, 得到完整的机载单光子探测系统. 然后按照测试标准GJB150.16 A-2009《军用装备实验室环境试验方法 第16部分: 振动试验》和GJB150.16 A-2009《军用装备实验室环境试验方法 第18部分: 冲击试验》进行整机测试, 将整个系统固定在水平振动平台和垂直振动平台上, 共3个方向(水平x/y轴, 垂直z轴), 每个方向振动1 h. 这3 h的测试过程中, 探测器一直有稳定的输出信号, 说明电路和系统均完好.
4. 结 论
本文基于NbN超导薄膜设计并制备出了四通道结构且能分辨16个光子数的SNSPD, 光敏面积为60 μm × 60 μm, 在温度低于3.5 K时4个通道量子效率均达到饱和, 在温度为4.2 K时4个通道量子效率均大于50%. 器件设计采用窄线宽纳米线来提高探测器的量子效率, 增加了效率的饱和区间长度, 并克服了因温度上升导致量子效率下降的问题, 成功将SNSPD的工作温度提高至液氦温区. 本文制备的器件还通过并联电阻的方式实现了光子数分辨功能, 有助于探测系统获取更多信息从而提高探测精度, 可为机载探测器件提供复杂机载环境下目标的高精度探测数据.
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图 2 纳米线扫描电子显微镜图: 总面积为60 μm × 60 μm, 共四个通道, 每个通道包括4个像元(①②③④). 红色圆虚线表示入射光斑大小, 直径为60 μm. 绿色线框表示1号通道左、中、右3个位置处的纳米线, 线宽为65 nm ± 2 nm, 分布较为均匀
Fig. 2. Scanning electron microscopy of nanowires: total area is 60 μm × 60 μm, four channels, each channel includes four pixels (①②③④). The red dotted line is the size of the incident light spot, with a diameter of 60 μm. The green line frame is the nanowire at the left, middle and right of Channel 1, with a line width of 65 nm ± 2 nm and relatively uniform distribution.
图 3 器件性能测试 (a) 器件在不同温度下的量子效率, 在温度小于3.5 K时四通道量子效率均达饱和, 但饱和区间长度随着温度上升而减小, 当温度升至4.2 K时, 通过对实验结果的拟合, 得到4个通道的量子效率均大于50%; (b) 光子响应幅值分布统计, 呈现4个高斯分布, 统计分布的中心值分别为56 , 72, 87, 98 mV, 分别对应单光子、双光子、三光子和四光子响应情况; (c) 通过示波器采集不同光子数响应的脉冲信号, 单光子响应时的信噪比为56 mV/20 mV ≈ 2.8
Fig. 3. Device performance test: (a) Quantum efficiency test of the device at different temperatures. The quantum efficiency of all four channels saturates at temperatures less than 3.5 K, but the length of the saturation interval decreases as the temperature rises. When the temperature rises to 4.2 K, the quantum efficiency of the four channels is obtained by fitting the experimental results, which is greater than 50%; (b) the statistics of photon response amplitude distribution, showing four Gaussian distributions with the center values of statistical distributions of 56 , 72 , 87 and 98 mV, corresponding to the single-photon, two-photon, three-photon and four-photon response cases, respectively; (c) the acquisition of different photon number response by oscilloscope, and the signal-to-noise ratio of single photon response is 56 mV/20 mV ≈ 2.8.
图 4 时间特性测试 (a) 单光子响应模式下时间抖动测量; 由于器件单通道包含了4个像元, 不同像元之间信号传输线的长度不同, 导致信号传输时间不同, 在时间轴上表现为4个高斯分布的叠加; (b) 多光子响应时时间抖动测量; 由于存在双光子、三光子和四光子响应多种状态, 在时间轴上无明显的分布特征; (c) 四光子响应时间抖动测量; 只存在4个像元同时响应的情况, 因此只有一个高斯分布, 此时抖动最小, 高斯分布半高宽110 ps
Fig. 4. Time characteristic test: (a) Timing jitter measurement in single-photon response mode. Because the single channel of the device contains four pixels, the length of signal transmission lines between different pixels is different, resulting in different signal transmission time, which is shown as the superposition of four Gaussian distributions on the time axis. (b) Measurement of timing jitter in multi-photon response. Due to the existence of two-photon, three-photon and four-photon response states, there is no obvious distribution characteristics on the time axis. (c) Four-photon response timing jitter measurement. Only four pixels respond at the same time, so there is only one Gaussian distribution. At this time, the jitter is minimum, and the half-height width of the Gaussian distribution is 110 ps.
表 1 液氦温区SNSPD国内外研究进展
Table 1. Progress of domestic and international research on SNSPD in liquid helium temperature region.
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[1] Henriksson M, Jonsson P 2018 Opt. Eng. 57 093104
[2] Kong H J, Kim T H, Jo S E, Oh M S 2011 Opt. Express 19 19323
Google Scholar
[3] Cohen L, Matekole E S, Sher Y, Istrati D, Eisenberg H S, Dowling J P 2019 Phys. Rev. Lett. 123 203601
Google Scholar
[4] Chang J, Los J W N, Tenorio-Pearl J O, Noordzij N, Gourgues R, Guardiani A, Zichi J R, Pereira S F, Urbach H P, Zwiller V, Dorenbos S N, Esmaeil Zadeh I 2021 APL Photonics 6 036114
Google Scholar
[5] Korzh B, Zhao Q Y, Allmaras J P, Frasca S, Autry T M, Bersin E A, Beyer A D, Briggs R M, Bumble B, Colangelo M, Crouch G M, Dane A E, Gerrits T, Lita A E, Marsili F, Moody G, Peña C, Ramirez E, Rezac J D, Sinclair N, Stevens M J, Velasco A E, Verma V B, Wollman E E, Xie S, Zhu D, Hale P D, Spiropulu M, Silverman K L, Mirin R P, Nam S W, Kozorezov A G, Shaw M D, Berggren K K 2020 Nat. Photonics 14 250
Google Scholar
[6] Reddy D V, Nerem R R, Nam S W, Mirin R P, Verma V B 2020 Optica 7 1649
Google Scholar
[7] Shibata H, Shimizu K, Takesue H, Tokura Y 2015 Opt. Lett. 40 3428
Google Scholar
[8] Zhang W, Huang J, Zhang C, You L, Lv C, Zhang L, Li H, Wang Z, Xie X 2019 IEEE Trans. Appl. Supercond. 29 2200204
Google Scholar
[9] Cahall C, Nicolich K L, Islam N T, Lafyatis G P, Miller A J, Gauthier D J, Kim J 2017 Optica 4 1534
Google Scholar
[10] Divochiy A, Marsili F, Bitauld D, Gaggero A, Leoni R, Mattioli F, Korneev A, Seleznev V, Kaurova N, Minaeva O, Gol'tsman G, Lagoudakis K G, Benkhaoul M, Lévy F, Fiore A 2008 Nat. Photonics 2 302
Google Scholar
[11] Mattioli F, Zhou Z, Gaggero A, Gaudio R, Leoni R, Fiore A 2016 Opt. Express 24 9067
Google Scholar
[12] Zhu D, Zhao Q Y, Choi H, Lu T J, Dane A E, Englund D, Berggren K K 2018 Nat. Nanotechnol. 13 596
Google Scholar
[13] Liao S K, Cai W Q, Liu W Y, Zhang L, Li Y, Ren J G, Yin J, Shen Q, Cao Y, Li Z P, Li F Z, Chen X W, Sun L H, Jia J J, Wu J C, Jiang X J, Wang J F, Huang Y M, Wang Q, Zhou Y L, Deng L, Xi T, Ma L, Hu T, Zhang Q, Chen Y A, Liu N L, Wang X B, Zhu Z C, Lu C Y, Shu R, Peng C Z, Wang J Y, Pan J W 2017 Nature 549 43
Google Scholar
[14] Guan Y, Li H, Xue L, Yin R, Zhang L, Wang H, Zhu G, Kang L, Chen J, Wu P 2022 Opt. Lasers in Eng. 156 107102
Google Scholar
[15] Borst J W, A Visser 2010 Meas. Sci. Technol. 21 102002
Google Scholar
[16] Sprengers J P, Gaggero A, Sahin D, Jahanmirinejad S, Frucci G, Mattioli F, Leoni R, Beetz J, Lermer M, Kamp M, Hofling S, Sanjines R, Fiore A 2011 Appl. Phys. Lett. 99 181110
Google Scholar
[17] Korner C 2007 Trends Ecol. Evol. 22 569
Google Scholar
[18] Pobell F 2007 Matter and Methods at Low Temperature (Verlag, Berlin, Heidelberg: Springer)
[19] Caloz M, Perrenoud M, Autebert C, Korzh B, Weiss M, Schonenberger C, Warburton R J, Zbinden H, Bussieres F 2018 Appl. Phys. Lett. 112 061103
Google Scholar
[20] Chen Q, Ge R, Zhang L, Li F, Zhang B, Jin F, Han H, Dai Y, He G, Fei Y, Wang X, Wang H, Jia X, Zhao Q, Tu X, Kang L, Chen J, Wu P 2021 Sci. Bull. 66 965
Google Scholar
[21] Kuzanyan A A, Nikoghosyan V R, Kuzanyan A S 2017 Proc. SPIE 10229 102290P
[22] Velasco A E, Cunnane D P, Frasca S, Melbourne T, Acharya N, Briggs R, Beyer A D, Shaw M D, Karasik B S, Wolak M A, Verma V B, Lita A E, Shibata H, Ohkubo M, Zen N, Ukibe M, Xi X X, Marsili F 2017 Conference on Lasers and Electro-Optics October 26, 2017, San Jose, CA, USA p1
[23] Salvoni D, Ejrnaes M, Parlato L, Yang X Y, You L X, Wang Z, Pepe G P, Cristiano R 2020 J. Phy.: Conf. Ser. 1559 012014
Google Scholar
[24] Gourgues R, Los J W N, Zichi J, Chang J, Kalhor N, Bulgarini G, Dorenbos S N, Zwiller V, Zadeh I E 2019 Opt. Express 27 24601
Google Scholar
[25] Wollman E E, Verma V B, Beyer A D, Briggs R M, Korzh B, Allmaras J P, Marsili F, Lita A E, Mirin R P, Nam S W, Shaw M D 2017 Opt. Express 25 26792
Google Scholar
[26] Gemmell N R, Hills M, Bradshaw T, Rawlings T, Green B, Heath R M, Tsimvrakidis K, Dobrovolskiy S, Zwiller V, Dorenbos S. N, Crook M, Hadfield R H 2017 Supercond. Sci. Technol. 30 11LT01
Google Scholar
[27] Hofherr M, Rall D, Ilin K, Siegel M, Semenov A, Hubers H W, Gippius N A 2010 J. Appl. Phys. 108 014507
Google Scholar
[28] Marsili F, Najafi F, Dauler E, Bellei F, Hu X L, Csete M, Molnar R J, Berggren K K 2011 Nano lett. 11 2048
Google Scholar
[29] Li F, Han H, Chen Q, Zhang B, Bao H, Dai Y, Ge R, Guo S, He G, Fei Y, Yang S, Wang X, Wang H, Jia X, Zhao Q, Zhang L, Kang L, Wu P 2021 Photonics Res. 9 389
Google Scholar
[30] Kozorezov A G, Lambert C, Marsili F, Stevens M J, Verma V B, Allmaras J P, Shaw M D, Mirin R P, Nam S W 2017 Phys. Rev. B 96 054507
Google Scholar
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