Dark count rate and band to band tunneling optimization for single photon avalanche diode topologies

This paper proposes two optimal designs of single photon avalanche diodes(SPADs) minimizing dark count rate(DCR). The first structure is introduced as p^+/pwell/nwell, in which a specific shallow pwell layer is added between p^+and nwell layers to decrease the electric field below a certain threshold. The simulation results show on average 19.7%and 8.5% reduction of p^+/nwell structure’s DCR comparing with similar previous structures in different operational excess bias and temperatures respectively. Moreover, a new structure is introduced as n+/nwell/pwell, in which a specific shallow nwell layer is added between n+and pwell layers to lower the electric field below a certain threshold. The simulation results show on average 29.2% and 5.5% decrement of p^+/nwell structure’s DCR comparing with similar previous structures in different operational excess bias and temperatures respectively. It is shown that in higher excess biases(about 6 volts), the n+/nwell/pwell structure is proper to be integrated as digital silicon photomultiplier(dSiPM) due to low DCR. On the other hand, the p^+/pwell/nwell structure is appropriate to be utilized in dSiPM in high temperatures(above 50?C) due to lower DCR value.

Modification of spontaneous emission rate of micrometer-sized light sources using hollow-core photonic crystal fibers

We investigate numerically and experimentally the modification of the spontaneous emission rate for micrometersized light sources embedded in a hollow-core photonic crystal fiber （HCPCF）. The diameter of the light source is deliberately chosen such that they could be easily introduced into the central hole of the hollow-core photonic crystal fiber by capillary force. The photoluminescence from the microparticles is measured by using an inverted microscope in combination with a spectrometer. The modification of the spontaneous emission rate is observed in a wavelength region where there is no band gap. The experimental observations are consistent with the simulation results obtained by the plane wave expansion and finite-difference time-domain techniques.

Study of the Photon Flux and the Dose Rate in the Vicinity of a 60Co Gamma Irradiator

The present work presents an overview of the study of some dosimetric quantities in the vicinity of the Tunisian Gamma Irradiation Facility. Firstly, we have confirmed our previous calculation of the photon flux and the dose rates, using a simulation with GEANT 4. A good agreement between calculation and simulation was obtained, which well confirmed the modeling of the CNSTN extended source by a pencil-like source. Secondly we have determined the isodose curves in the vicinity of the irradiator using a straightforward calculation. Finally, we have presented many comments for some published work concerning the methods used to determine these dosimetric quantities.

Significance of functional hepatic resection rate calculated using 3D CT/^(99m)Tc-galactosyl human serum albumin singlephoton emission computed tomography fusion imaging

AIM: To evaluate the usefulness of the functional hepatic resection rate(FHRR) calculated using 3D computed tomography(CT)/^(99m)Tc-galactosyl-human serum albumin(GSA) single-photon emission computed tomography(SPECT) fusion imaging for surgical decision making. METHODS: We enrolled 57 patients who underwent bi- or trisectionectomy at our institution between October 2013 and March 2015. Of these, 26 patients presented with hepatocellular carcinoma, 12 with hilar cholangiocarcinoma, six with intrahepatic cholangiocarcinoma, four with liver metastasis, and nine with other diseases. All patients preoperatively underwent three-phase dynamic multidetector CT and ^(99m)Tc-GSA scintigraphy. We compared the parenchymal hepatic resection rate(PHRR) with the FHRR, which was defined as the resection volume counts per total liver volume counts on 3D CT/^(99m)Tc-GSA SPECT fusion images.RESULTS: In total, 50 patients underwent bisectionectomy and seven underwent trisectionectomy.Biliary reconstruction was performed in 15 patients, including hepatopancreatoduodenectomy in two. FHRR and PHRR were 38.6 ± 19.9 and 44.5 ± 16.0, respectively; FHRR was strongly correlated with PHRR. The regression coefficient for FHRR on PHRR was 1.16(P < 0.0001). The ratio of FHRR to PHRR for patients with preoperative therapies(transcatheter arterial chemoembolization, radiation, radiofrequency ablation, etc.), large tumors with a volume of > 1000 m L, and/or macroscopic vascular invasion was significantly smaller than that for patients without these factors(0.73 ± 0.19 vs 0.82 ± 0.18, P < 0.05). Postoperative hyperbilirubinemia was observed in six patients. Major morbidities(Clavien-Dindo grade ≥ 3) occurred in 17 patients(29.8%). There was no case of surgeryrelated death.CONCLUSION: Our results suggest that FHRR is an important deciding factor for major hepatectomy, because FHRR and PHRR may be discrepant owing to insufficient hepatic inflow and congestion in patients with preoperative therapies, macroscopic vascular invasion, and/or a tumor volume of > 1000 m L.

室温下高探测效率InGaAsP/InP单光子雪崩二极管

描述了一种高性能平面InGaAsP/InP单光子雪崩二极管(SPAD),该二极管具有单独的吸收、分级、电荷和倍增(SAGCM)异质结构。通过电场调节和缺陷控制,SPAD在293 K的门控模式下工作,光子探测效率(PDE)为70%,暗计数率(DCR)为14.93 kHz,后脉冲概率(APP)为0.89%。此外,在死区时间为200 ns的主动淬灭模式下工作时,室温下实现了12.49%的PDE和72.29 kHz的DCR。

488nm泵浦的自发参量下转换特性研究

自发参量下转换的光谱、光子数率和时间相关性对宽波段光电探测器定标具有重要意义。本文理论模拟了488 nm连续激光泵浦偏硼酸钡(BBO)晶体的光谱和光子数率的分布,搭建了光谱、光子数率和时间相关性测量的实验系统。基于理论研究,BBO晶体的相位匹配角选择24.3184°,可实现605~2523 nm连续宽波段相关光子制备,光子数率最大值为4.2716×10^(7) s^(-1)。采用CMOS相机和光电倍增管测量相关光子圆环和光子数率,根据波长和探测器响应波段来选择相应的光电探测器,以测量时间相关性。实验测量得到605~1000 nm波段的相关光子光谱,光子数率的实测值与理论值偏差在1个量级内,并观察到710~1560 nm波段的符合峰。实验结果验证了所建立的理论模型的正确性、自发参量下转换过程的宽光谱特性和时间相关性,为实现可见-近红外波段的宽光谱相关光子定标提供了研究基础。

SOI基横向SAMBM APD三维建模与特性研究

为更好表征器件的工作过程,为后续器件工艺制备实现提供更精确的理论支撑,采用SEN-TAURUS软件对SOI基横向多缓冲区SAM雪崩光电二极管进行三维建模仿真与特性研究。对器件的雪崩电压、光暗电流、响应度、雪崩增益、雪崩发生概率、光子探测效率以及暗计数率进行研究分析。仿真结果表明,器件雪崩电压为8.0 V,在偏置电压为4 V时,器件暗电流为5.31×10^(-16)A;当入射光波长为400 nm,光功率为0.001 W/cm^(2)时,响应度为170 A/W,增益为308.6;过偏压为1 V时,光子探测效率峰值为42.3%,暗计数率为476 Hz。

全身骨显像中肾脏显影异常的病因浅析

目的探讨全身骨显像中肾脏显影异常的发生情况并初步分析病因。方法回顾性分析2021年11月至2022年7月在我院行骨显像的患者1674例,对肾区不同类型的显影异常结合患者其他相关影像检查及临床资料进行定性评估。结果共发现肾脏显影异常147例(8.78%),其中肾实质显影明显54例(3.23%),肾脏集合系统(肾盏肾盂或输尿管)异常显影61例(3.64%),单肾不显影14例(0.84%),双肾不显影23例(1.37%),肾脏位置异常8例(0.48%)等异常,并对不同类型显影异常的可能病因进行了分析。结论骨显像中肾脏显影出现异常,可提示肾脏结构异常、尿路排泄障碍以及肾脏功能异常等情况,可引导临床按需要行进一步检查,以明确疾病的原因,对临床诊治具有一定的指导意义。

Explore QCD phase transition with thermal photons

This pilot study was to assess the high temperature and zero baryon density region of quantum chromodynamics(QCD) phase diagram with thermal photon emission,where the nature of QCD phase transition is ambiguous.Based on a(3+1)-D ideal hydrodynamical model to describe macroscopically the collision system,thermal photons emitted from Pb+Pb collisions at 2.76 TeV are investigated.The result reveals that photons from heavy ion collisions at high energy and centrality are possible to distinguish the structure of the hot dense matter,in QGP phase or hadronic phase,thus may provide an approach to explore the nature of this finite-temperature QCD transition(that is,first-order,second-order or analytic crossover).

ICESat-2数据背景光子特性及滤波方法研究

ICESat-2(Ice,Cloud and Land Elevation Satellite-2)是世界首颗采用光子计数模式的激光测高卫星,可快速获得高精度、大尺度地面三维数据。光子探测机制使得数据中除了地面信号外,还包含大气散射等背景信号,需要通过滤波才能获得地形等信息。为分析ICESat-2背景和信号光子的分布特点及点云滤波算法的效果和适用性,本文首先选取了六种地表覆盖类型(城市、海冰、沙漠、植被、海洋及冰盖/冰川)及不同观测条件的数据,对其背景光子率进行统计分析。分析结果表明:白天观测数据的背景光子率平均为106(点/秒)数量级,远高于夜晚观测数据的背景光子率——104(点/秒)数量级,弱波束的背景光子率与强波束背景光子率相当,六种地表覆盖类型中,冰盖/冰川的背景光子率最高。然后,根据统计结果筛选出21组测高数据,并选取七种具有代表性的点云滤波对其进行去噪实验,分析精度后得出结论:改进局部密度法的去噪效果最佳,算法召回率、精准度和F值均大于0.90,算法较为稳定。最后,对所选取各滤波算法的精度、特点与适用性等性质进行了总结与分析,可为后续该数据的使用和滤波算法的选择提供参考。

Calculation and analysis of the number of return photons from sodium laser beacon excited by the long pulse laser with circular polarization

The number of return photons from sodium laser beacon（SLB） greatly suffers down-pumping, recoil, and geomagnetic field when the long pulse laser with circular polarization interacts with sodium atoms in the mesosphere. Considering recoil and down-pumping effects on the number of return photons from SLB, the spontaneous radiation rates are obtained by numerical computations and fittings. Furthermore, combining with the geomagnetic field effects, a new expression is achieved for calculating the number of return photons. By using this expression and considering the stochastic distribution of laser intensity in the mesosphere under different turbulence models for atmosphere, the number of return photons excited by the narrow-band single mode laser and that by the narrow-band three-mode laser are respectively calculated. The results show that the narrow-band three-mode laser with a specific spectrum structure has a higher spontaneous radiation rate and more return photons than a narrow-band single mode laser. Of note, the effect of the atmospheric turbulence on the number of return photons is remarkable. Calculation results indicate that the number of return photons under the HV5/7 model for atmospheric turbulence is much higher than that under the Greenwood and Mod HV models.

Spin Dependent Selection Rules for Photonic Transitions in Hydrogen-Like Atoms

Spin dependent selection rules for photonic transitions in hydrogen-like atoms is derived by using the solution of Dirac equation for hydrogen-like atoms. It is shown that photonic transitions occur when [ Δj=0,±1,±2, while Δmj=0,±1,±2 ]. By applying the spin dependent selection rules, we can explain the observed (6s→7s) transition in Cesium (Cs) atom.

基于微波光子学的光载超宽带信号产生和传输技术

光载超宽带技术因兼具超宽带信号大带宽、传输速率高等优点和光纤传输的远距离传输、损耗小等优势而在近年来备受关注。文章提出一种基于微波光子技术产生超宽带(UWB)信号的系统,该方案基于非线性PM-IM转换,产生一阶超宽带信号,然后又用平衡光电探测器(BPD)和光延迟线构建延迟线滤波器对其进行一阶差分,产生了符合美国联邦通信委员会(FCC)掩膜要求的二阶超宽带信号。系统最终产生的二阶超宽带信号的频谱具有大约5.4 GHz的中心频率和4.3 GHz的10 dB带宽。另外,还提出了一种基于直接序列-二进制相移键控调制(DS-BPSK),并使用卷积编码进行信道编码,然后使用啁啾布拉格光栅对信号进行色散补偿的信号处理技术。通过Opti-system软件进行仿真验证,在前向纠错门限为3.8×10^(-3)时,接收机灵敏度提升了约5.5 dBm,有效降低了误码率,提升了光载超宽带系统的传输性能。

一种宽光谱响应的双结单光子雪崩二极管

基于180 nm BCD工艺提出了一种新型双结雪崩区的单光子雪崩二极管(SPAD)探测器,采用N阱/高压P阱/N^(+)埋层结构形成了两个垂直堆叠的PN结,高压P阱和N^(+)埋层交界面形成较深的主雪崩区,增强对近红外短波光子的探测概率;同时,N阱/高压P阱之间形成浅的次雪崩区,实现对蓝绿光的高效探测,两结同时工作能够有效扩展器件的光谱响应范围。TCAD仿真结果表明,与传统的P阱/深N阱结构相比,双结SPAD器件在300~940 nm的宽光谱范围内有更高的光子探测概率,在800 nm近红外短波段探测概率达到了20.6%。在3 V过偏压下,暗计数率为0.8 kHz,后脉冲概率为3.2%。

大型客体光子计数成像技术的发展与挑战

具有光子计数能力的探测器给辐射成像领域带来了技术革新,具有巨大的应用潜力。光子计数探测器凭借其能量分辨能力将有助于提高辐射图像质量、降低辐射剂量、提高检测效率。目前,光子计数成像技术在医学诊断和行包安检等低能领域已有广泛和深入的研究,比如在能谱CT、乳腺检查、PET等领域诞生了许多成果,但是在集装箱检测及车辆安检等大型客体检测的中高能(MeV)领域研究较少,还需进一步克服技术上的困难,以达到中高能射线和高计数率条件的应用要求。本研究重点介绍了光子计数成像技术的特征优势、在X/γ射线医学诊断、安全检查辐射成像系统中的研究现状及面临的挑战,分析了其在大型客体检测中的应用现状和需要进一步突破的技术难点。

遮荫条件下绞股蓝光合作用特点的研究

在夏季遮荫条件下栽培绞股蓝的净光合速率日变化呈现不典型的双峰曲线 ,第 1峰值出现在11:0 0时 ,达 13 8μmolCO2 ·m-2 ·s-1;日净光合速率达到 176 97μmolCO2 ·m-2 ,是强光下栽培的 3 1倍 ;净光合速率和光量子通量密度呈正相关 ,相对湿度对净光合速率的影响小 .强光下栽培绞股蓝 ,光合作用“午休”现象明显 ,净光合速率日变化呈现双峰曲线 ,第 1峰值出现在 10 :0 0时 ,为 3 0 μmolCO2 ·m-2 ·s-1,第 2峰值出现在 14 :0 0时 ,为 1 2 5 μmolCO2 ·m-2 ·s-1;相对湿度与净光合速率成正相关 ,对净光合速率的影响大 .当光量子通量超过 70 0 μmol·m-2 ·s-1时 ,净光合速率与光量子通量密度呈负相关 .在影响该植物蒸腾速率的诸多因子中 ,蒸腾速率和气孔导度之间的相关性最为显著 .因此绞股蓝属于高度耐荫而怕光的植物 ,人工栽培应重点考虑光照因子 .

可调红蓝光子比例的LED植物光源配光设计方法

为了动态控制用于植物生长的人工光源，该文提出一种以光子数作为评价标准，使红蓝光比例连续可调的LED植物生长光源的配光方法。综合考虑红、蓝2种波段光源及其他光谱的作用，该文采用白光LED与红光LED 组合配比，以正向电流下 LED 的光谱密度数据作为计算基础，提出配光设计算法，实现红蓝成分有效光子数维持一定的要求下，红光与蓝光光子数比在指定区间（4：1～9：1之间）连续可调，从而满足植物不同生长状态对光质成分的需要。

参棚透光率对西洋参叶片光合作用的影响

研究了参棚透光率与西洋参叶片净光合速率之间的关系 .结果表明 ,西洋参叶片光饱和点、净光合速率及其日变型均随参棚透光率的不同 ,存在一定的差异 .4年生西洋参叶片在 12 %、30 %、4 2 % 3种透光率下 (气温 2 9.0℃左右 ) ,光饱和点分别为 171.0、32 3.0和 4 2 9.0 μmol·m-2 ·s-1,净光合速率最大值为6 .5 4mg·dm-2 ·h-1(CO2 ) ,出现在透光率为 30 %的参棚下 ;3年生西洋参在透光率不超过 2 5 .8%的参棚下 ,叶片净光合速率日变化呈单峰型 ,透光率大于 2 5 .8%时 ,呈双峰型 ,参叶“光合午休”现象明显 .单相关分析表明 ,光量子通量密度是影响西洋参净光合速率的主要因子 ;回归分析结果表明 。

光在一维随机分布光子晶体中的传播

用特征矩阵法计算了光波在一维随机分布的光子晶体中的传播规律 ,与周期性结构相比较 ,在此种结构的光子晶体中带隙结构几乎消失 ,光波透射率与随机度、频率。

基于Geant4的多相流CT系统优化设计

针对多相流CT系统,利用基于蒙特卡洛方法的高能粒子输运仿真软件工具包Geant4分析,构建了多相流CT系统5源、7源和9源仿真模型.分析多相流CT系统的数学模型,并利用LBP、FBP以及ART算法进行了图像重建.基于散射光子比和重建图像质量等优化指标分析,进行了多相流CT成像系统的优化设计.实验表明,优化设计后的CT系统使层流、环流和泡状流的散射光子比分别降低到5.32%、5.33%和5.29%,有效抑制了光子散射,明显改善了再构图像质量.