α-clustering effect on flows of direct photons in heavy-ion collisions

In this study,we reconstruct theγ-photon energy spectrum,which is in good agreement with the experimental data of ^(86)Kr+^(12)C at E/A=44 Me V within the framework of the modified EQMD model.The directed and elliptic flows of free protons and direct photons were investigated by considering theα-clustering structure of ^(12)C.Compared with free protons,direct photon flows provide clearer information about the early stage of a nuclear reaction.The difference in the collective flows between different configurations of ^(12)C is observed in this study.This indicates that the collective flows of direct photons are sensitive to the initial configuration.Therefore,theγbremsstrahlung process might be taken as an alternative probe to investigate theα-clustering structure in a light nucleus from heavy-ion collisions within the Fermienergy region.

The Influence of EMC Effect on Large Transverse Momentum Direct Photon Production

Using the statistical model of parton and applying the rescaling model tochoose nuclear parameters by fitting the experimental data in low-X and medium-X re-gion,the influence of EMC(European Muon Collaboration)effect on large-P_T directphoton production is studied.The result shows that the influence of EMC effect issmall.

Economical quantum secure direct communication network with single photons

In this paper a scheme for quantum secure direct communication （QSDC） network is proposed with a sequence of polarized single photons. The single photons are prepared originally in the same state （0） by the servers on the network, which will reduce the difficulty for the legitimate users to check eavesdropping largely. The users code the information on the single photons with two unitary operations which do not change their measuring bases. Some decoy photons, which are produced by operating the sample photons with a Hadamard, are used for preventing a potentially dishonest server from eavesdropping the quantum lines freely. This scheme is an economical one as it is the easiest way for QSDC network communication securely.

Design of a compact polarization beam splitter based on a deformed photonic crystal directional coupler

In this paper a compact polarization beam splitter based on a deformed photonic crystal directional coupler is designed and simulated. The transverse-electric （TE） guided mode and transverse-magnetic （TM） guided mode are split due to different guiding mechanisms. The effect of the shape deformation of the air holes on the coupler is studied. It discovered that the coupling strength of the coupled waveguldes is strongly enhanced by introducing elliptical airholes, which reduce the device length to less than 18.Sttm. A finite-difference tlme-domain simulation is performed to evaluate the performance of the device, and the extinction ratios for both TE and TM polarized light are higher than 20 dB.

微波光子联合时差/相差的高精确度测向技术

针对短基线时差测向精确度低、长基线相差测向存在模糊和传统的微波技术难以满足电子战设备分布式部署的长距离传输需求的问题,结合微波光子学,提出一种基于微波光子联合时差相差的分布式长距离单基线高精确度测向技术。该技术使用直调模式微波光子传输设备,克服了微波信号经过长距离传输后引起的时差和相差变化影响,满足长距离微波光子的稳定传输;并在此基础上采用改进的时差曲面拟合插值方法解决相差模糊问题。仿真和实验测试验证了该技术实现分布式长距离单基线高精确度测向的可行性。

磁化等离子体交替隐式时域有限差分法

针对传统显式时域有限差分法仿真各向异性磁化等离子体时,时间步长会受到柯朗-费里德里希斯-列维(Courant-Friedrich-Levy,CFL)条件限制的问题,采用拓展的无条件稳定交替隐式时域有限差分方法(alternating-direction-implicit finite-difference time-domain,ADI-FDTD)对无限大磁化等离子体进行数值仿真。该方法在传统两步法基础上增加2个子时间步,同时仍保持无条件稳定的特性。实验结果表明:反射和透射系数与理论值吻合较好。与普通时域有限差分方法相比,该方法能够高效仿真等离子体光子晶体,并且具有较高的精度和无条件稳定的特性。

金属微纳结构操控单光子发射体辐射

固态单光子发射体结合了原子优异的光学性质(如高可靠性、高效率等)和固态系统的便利性与可扩展性,在可扩展光量子信息技术中扮演着重要角色。然而,真空中固态单光子发射体所发出的单光子具有自发辐射速率低、各向同性发射、发射光的偏振状态随机等不足,这极大地限制了其应用。金属微纳结构支持的表面等离激元具有巨大的场增强和亚波长的场束缚效应,因此国内外研究者设计了各种各样的金属微纳结构来操控单光子发射体的辐射。本研究综述了金属微纳结构在单光子发射体自发辐射增强、准直辐射、辐射偏振操控等方面的研究进展,重点比较了性能指标并分析了操控机制。最后,对金属微纳结构操控单光子发射体辐射的挑战和发展进行了展望。

Photon Emission from Quark Gluon Plasma at RHIC and LHC

We work on photon production through annihilation and Compton, and annihilation with scattering (AWS) processes through a quark-gluon plasma (QGP) in high energy nuclear collision incorporating the parametrization factors in strong coupling value and thermal dependent quark mass obtained through a coupling value. We find that photon yield increases with the increasing of the temperature and dominated by early times. We also compare the influence of coupling value on the spectrum of thermal photons. The production rate of photons is observed in the range of low and intermediate transverse momentum. The results are compared with other work.

Wave Transmission in Dispersive Si-Based One Dimensional Photonic Crystal

Transmission of electromagnetic waves through a Si-based one dimensional photonic crystal has been investigated. The proposed structure works as an omni-directional reflector for a certain range of wavelength for an angle of incidence up to 55?. The structure works as a narrow band TM-polarization filter for an angle of incidence more than 55?, i.e. a filter which completely blocks TE-polarized waves but allows certain wavelengths of TM-polarized waves. But at an angle of incidence of 89?, the structure works as a multiple narrow band TM-polarization filter even though no defect layer is introduced inside the structure. It is also found that this multiple narrow pass-bands of TM-polarized waves can be tuned to a desired range of wavelength by changing the temperature of the structure.

Intensity Dependent Nonlinear Absorption in Direct and Indirect Band Gap Crystals under Nano and Picosecond Z-Scan

The nonlinear absorption properties of direct (GaN) and indirect (CdI2) band gap crystals have been studied by using an open aperture Z-scan technique under fundamental (1064 nm) and frequency doubled (532 nm) wavelength respectively with 10 ns or 60 ps pulse durations. Direct band gap crystal exhibits two and three photon absorption at all input irradiances. On the other hand, at low input irradiance the indirect band gap crystal exhibits saturable absorption (SA). At higher input irradiances two and three photon absorption becomes dominant. A monotonic increase of the nonlinear absorption coefficients with increasing laser pulse duration from 60 ps to 10 ns is observed for GaN and CdI2 crystals.

The Weak Magnetic Photon Emission from Quark-gluon Plasma

There must be electromagnetic fields created during high-energy heavy-ion collisions.Although the electromagnetic field may become weak with the evolution of the quark-gluon plasma(QGP),compared to the energy scales of the strong interaction,they are potentially important to some electromagnetic probes.In this work,we propose the coupled effect of the weak magnetic field and the longitudinal dynamics of the background medium for the first time.We demonstrate that the induced photon spectrum can be highly azimuthally anisotropic when the quarkgluon plasma is in the presence of a weak external magnetic field.On the other hand,the weak magnetic photon emission from quark-gluon plasma only leads to a small correction to the photon production rate.After hydrodynamic evolution with a tilted fireball configuration,the experimentally measured direct photon elliptic flow is well reproduced.Meanwhile,the used time-averaged magnetic field in the hydrodynamic stage is found no larger than a few percent of the pion mass square.

基于飞秒激光的高速双光子刻写技术

基于飞秒激光的双光子聚合(two-photon polymerization,TPP)加工技术一直是三维微纳加工技术中的研究热点。随着生命科学、材料工程、微纳光学等领域对复杂、大面积微型三维器件制备需求的提升,TPP加工效率不足的问题日益严重,加工时间过长不仅造成加工结构的不稳定,更是严重阻碍这些重要三维器件的进一步推广应用。本文以TPP加工效率提升方面的研究工作为主线,分别从单光束刻写、并行多光束刻写、面曝光和体曝光四个方式进行总结与对比,阐述相应的光学系统设计、刻写策略、刻写精度与通量等方面的研究情况,总结各种技术的优势与劣势,同时展望未来发展趋势。

基于高精度3D打印工艺的ICF调制靶

惯性约束聚变(ICF)中的瑞利-泰勒不稳定性(RTI)研究需要基于多种结构的调制靶,针对目前调制靶制备的工艺问题,采用双光子3D打印工艺制备了平面调制、平面复合调制及球壳型调制三种典型结构的调制靶,靶材料为光敏树脂(95%:C_(23)H_(38)N_(2)O_(8),5%:C_(4)H_(6)O_(2))。采用激光共聚焦显微成像分析了三种调制靶的实际结构参数,三种靶型的实测形貌及其参数与设计结构及参数具有良好匹配度。为进一步验证双光子3D打印新型工艺制备调制靶的可行性,实验团队在“神光Ⅱ”高功率激光实验装置上进行了纳秒激光打靶实验,结果显示靶表面的调制在激光直接驱动下受RTI的作用随时间呈增长趋势,初始峰谷值为4μm的调制在激光驱动2.5 ns后形成了长度达100μm的高密度射流,表明基于高精度3D打印工艺制备结构复杂的调制靶用于RTI研究具有较高可行性。

光子晶体结构参数对直波导型模式转换器性能影响研究

为研究光子晶体结构参数改变对直波导结构的模式转化器效率的影响,通过改变光子晶体间距和形状两个参数,并结合时域有限差分法和直接二元搜索算法分析直波导型模式转化器对应转换效率。仿真结果表明,在正方形光子晶体间距为150 nm时,器件转换效率为94.8%,收敛时间为87分钟。在波长范围在1500 nm到1600 nm时,圆形光子晶体可在64 nm带宽范围内转换效率优于其他两种形状。

基于亚波长光栅的高性能定向耦合器的研究

在SOI平台上提出并设计了一种基于亚波长光栅(SWG)和非对称耦合型(ADC)波导的高带宽低损耗的定向耦合器。SWG结构嵌入在两条波导之间,可以有效提高TE模式的耦合强度。通过优化分析选择器件参数,并通过调整耦合区长度实现了不同功率分束比,包括50%/50%、60%/40%、70%/30%、80%/20%、90%/10%。在不同分束比下带宽均超过100 nm,插入损耗均小于0.3 dB,部分分束比下带宽大于150 nm,插入损耗小于0.2 dB。器件最小耦合区尺寸仅为7.4μm×1.2μm。

均匀圆阵下微波光子鉴相相关干涉仪测向算法

为实现高频段微波信号的精确测向,提出了一种基于微波光子鉴相器的均匀圆阵相关干涉仪测向算法。为克服传统的电域鉴相器工作频段低、带宽窄的缺点,利用微波光子技术高频段、大带宽、低损耗和抗电磁干扰的优点,基于双偏振调制器设计一种微波光子鉴相器,利用光干涉将相位差信息映射为光信号功率,通过测量功率计算出相位差。该微波光子鉴相器精度高,能实现±180°的相位差测定,鉴相精度为±2°。利用余弦函数克服了传统相关干涉仪存在的相位模糊问题。同时,为确保算法的实时性,测向算法需选取适当的步进角度。为克服步进角度引入的测向误差,利用二维抛物面进行拟合插值运算,从而提高算法的精确度。最后,通过仿真验证了微波光子鉴相器和相关干涉仪测向算法的有效性。

激光直写氧化石墨烯可调光子筛

光子筛不受衍射极限限制且设计结构灵活,是一种新型衍射元件。相比于振幅型光子筛,相位型光子筛能量透过率更高,成像对比度更加尖锐,具有应用优势。然而,常见衍射光学器件面临加工复杂及难以调制等局限。石墨烯及其衍生材料具有良好的光电调制特性,被广泛用于衍射光学器件制备。利用激光直写技术可实现诱导还原氧化石墨烯,是一种简单高效的微纳加工技术。利用时域有限差分方法研究光子筛的衍射特性,并基于激光直写技术制备氧化石墨烯光子筛。通过不同激光功率加工可获得材料的折射率调制,器件实现了明显的焦距调制(1.62mm)和聚焦效率的提高(13.6%)。该方法有望为实现可调制衍射光学元件提供简便、灵活的设计与制备手段。

原子核同核异能态诱发辐射研究进展

介绍了同核异能态的特点和诱发同核异能态的几种机制,如直接光激发、电子跃迁诱导核激发(NEET)和电子俘获诱导核激发(NEEC)。同核异能态的诱发辐射研究目前在国际上竞争激烈,尤其是对最近提出的NEEC的研究。同时探讨了在我国开展这些研究的可能性。

一种基于光子晶体光纤的光纤旋转连接器设计

光纤旋转连接器因其具有传输带宽大、电磁兼容良好、体积小、寿命长等优点,有逐渐取代传统电滑环进行相对旋转平台间信息传输的趋势。提出一种利用大模场光子晶体光纤直接耦合的新型光纤旋转连接器的设计方案,耦合理论分析表明其不仅满足低插入损耗,而且具有结构简单、体积小、加工和装配精度要求相对较低等优点。大模场光子晶体光纤的无截止波长单模传输和低非线性传输特性使它能更有效地与WDM技术相结合提高传输容量,具有更广阔的应用。

一维光子晶体能带结构特性分析

基于平面波展开法,数值研究了不同参数对一维光子晶体带隙特征的影响。研究表明:归一化频率范围内的光入射一维光子晶体表面,产生多个光子带隙;当增大介质折射率差值时,带隙数量增多,带隙宽度增大,同时带隙中心频率向低频方向移动。实现全向光子禁带充要条件为,TE模式和TM模式的掠入射光锥内无传输态存在,同时,介质的布儒斯特角在光锥以外。