BaFBr：Eu2＋的发光及电特性研究

采用高温固相反应方法制备的BaFBr：Eu2 粉末样品，未经X射线、真空紫外或紫外光辐照，用波长大于400nm的光激发样品，可观测到Eu2 的390nm发光。样品的电子自旋共振(ESR)谱证实在BaFBr：Eu2 粉末样品的制备过程中，会产生大量的晶格缺陷，分别为电子和空穴陷阱，它们在光激励发光过程中充当不可缺少的角色。本工作将BaFBr：Eu2 粉末制成压片，在其一侧制作两个电极，以研究电阻-电压关系、剩余申压随时间的变化以及与电极材料的关系等电学特性。电特性研究结果也表明，样品中有电子和空穴陷阱两类缺陷，BaFBr：Eu2 的发光，源自激发能通过这两类缺陷向Eu2 的能量传递。     

BaFBr∶Eu2+的发光及电特性研究

采用高温固相反应方法制备的BaFBr∶Eu2+粉末样品,未经X射线、真空紫外或紫外光辐照,用波长大于400nm的光激发样品,可观测到Eu2+的390nm发光.样品的电子自旋共振(ESR)谱证实在BaFBr∶Eu2+粉末样品的制备过程中,会产生大量的晶格缺陷,分别为电子和空穴陷阱,它们在光激励发光过程中充当不可缺少的角色.本工作将BaFBr∶Eu2+粉末制成压片,在其一侧制作两个电极,以研究电阻-电压关系、剩余电压随时间的变化以及与电极材料的关系等电学特性.电特性研究结果也表明,样品中有电子和空穴陷阱两类缺陷,BaFBr∶Eu2+的发光,源自激发能通过这两类缺陷向Eu2+的能量传递.     

紫外线激发后KCl:Cu+的光激励发光

用固相反应法制备了KCl：Cu^＋多晶样品。经紫外光辐照后，用560nm的光照射能产生近紫外蓝光的光激励发光。研究表明，Cu^＋作为发光中心，经紫外光辐照后并没有产生Cu^＋到Cu^＋的变价，即Cu^＋不是空穴俘获中心，而阴离子空位充当电子陷阱。当激发后的样品受到光激励时，电子与空穴中心或Vk心复合后将能量传递给Cu^＋离子，产生d-s跃迁的特征发射。     

CaS∶Eu,Sm光存储材料的光谱特性

CaS∶Eu, Sm是一种典型的电子俘获型光存储材料,文章采用湿法在还原气氛中制备了CaS∶Eu, Sm粉末样品。测量了这种光存储材料的XRD、激发光谱、发射光谱、光激励发光光谱、热释光谱以及光激励发光衰减曲线。XRD结果表明样品在1 050 ℃晶格已经形成。光谱测试结果说明紫外光可激发该材料,作为信息写入光源。样品被紫外光源饱和激发后,用980 nm红外激光激励,发射出峰值位于635 nm的红光。光激励发光起初衰减较快,随后有一个较长的平缓期。且样品具有合适深度的陷阱能级,能够稳定存储信息。对CaS∶Eu, Sm的光存储机理进行了探讨。     

BaMgAl10O17:R2+(R=Eu,Mn)的真空紫外光谱特性

采用高温固相反应法合成了BaMgAl10O17:R(R＝Eu,Mn)荧光体，测量了荧光体的真空紫外激发光谱和相应的发射光谱，观察到基质吸收带位于165nm附近，Mn^2 离子的吸收位于170－240nm范围，Eu^2 离子的4f→5d吸收位于210－400nm范围。真空紫外光谱特性的研究表明基质与激活离子之间存在较好的能力传递。     

NaGdF4：Eu^3＋和GdBaB9O16的VUV荧光性质

在真空紫外光激发下，六方结构的NaGdF4:Eu^3 中的Gd^3 离子吸收一个光子，将能量分两步传递给Eu^3 离子，发生红色双光子发射。立方结构的NaGdF4:Eu^3 中存在一定量的氧离子取代缺陷，使Gd^3 离子4f-5d跃迁移到177nm附近，这与惰性气体放电产生的VUV光波长一致，并且其荧光色纯度较高。在VUV激发下，GdBaB9O16中的Gd^3 离子发生双光子（紫外和红色或远红外）发射。     

MO-Y2O3-B2O3:Re(M=Mg,Sr;Re=Eu,Tb)的真空紫外光谱特性

采用高温固相反应法合成了掺杂Eu3 及Tb3 的17MO-7.88Y2O3-75B2O3样品,研究了它们的光谱特性,结果表明,MO-T2O3-B2O3基质在真空紫外(VUV)区有很强的吸收,MgO-Y2O3-B2O3:Eu在147nm真空紫外光激发下产生对应于Eu3 的5D0→7FJ(J=1,2,3,4)跃迁的590和613 nm强发射峰;MgO-Y2O3-B2O3:Eu中Sr的引入使材料体系在147 nm附近的吸收和在613 nm附近的发射获得明显增强;MgO-Y2O3-B2O3:Tb的真空紫外激发谱除在147 nm附近的基质吸收外,还有对应于Tb3 的4f75d→4f8跃迁位于170,178,195,204,225 nm左右的一组谱峰,两者相互叠加使得材料在真空紫外区(120～220 nm)内都有很好的吸收.     

LiBaF3:Eu2+真空紫外光谱研究

在室温下，二价稀土离了 杂的LiBaF3:Eu^2 粉末样品中，Eu^2 的发射呈现双峰结构，有一峰值波长约为410nm的宽峰，对应于Eu^2 的5d-4f跃迁，以及另一峰值波长约为360nm的窄峰，对应于Eu^2 的4f-4f跃迁。在50－400nm波长范围，测量了样品的反射光谱，并利用Kramers-Kroenig关系，计算了吸收光谱。从吸收光谱中，可以看到在102nm处有明显的吸收边，得到LiBaF3材料的禁带宽度Eg约为12.1eV。在高能端有53.4,59.4,65.3,69.2和76.5nm的吸收峰，它们对应于Ba^2 的5p电子和F的2p电子芯能级之间的跃迁，在低能量的183.4nm处，有很明显的吸收峰，推测这对应于本征缺陷的吸收。更低能量的吸收峰，则对应于禁带中的一些杂质能级，在未经紫外光或X射线辐照之前，用长波长（＞450nm）光激发LiBaF3:Eu^2 粉末样品，可以观测到Eu^2 离子的360nm和410m发光，亦表现出光激励发光特性。     

Si基CeO_2薄膜的发光特性

利用电子束蒸发技术在p型硅衬底上沉积了200 nm厚的CeO2薄膜样品,将样品置于弱还原气氛中高温退火后,观察到薄膜在385,418 nm以及445 nm左右出现三个明显的发光峰。结合激发光谱、吸收光谱以及XRD分析表明:CeO2薄膜在高温下容易发生失氧反应,出现Ce4+→Ce3+离子转变,Ce3+离子在紫外光的激发下,电子由O2p跃迁到5d能级,再由5d能级向4f能级跃迁,从而产生强烈的蓝紫外发射,而445 nm左右的发光峰则来自于SiO2薄膜的缺陷发光。样品选择900~1 200℃不同温度退火,并且在1 200℃下进行了不同时间的退火。研究结果显示:在1 200℃下进行2 h的退火,薄膜发光强度达到最大。     

Al_(18)B_4O_(33)∶Cr~(3+)荧光粉的制备及发光性质研究

采用高温固相法合成了Al18B4O33∶Cr3+荧光粉,使用X射线粉末衍射仪和FSEM对样品的结构和形貌进行了表征,采用荧光分光光度计及紫外分光光度计研究了样品的发光性质及光吸收性质。结果表明,在紫外光或530~630 nm可见光激发下,样品能够发射出660~720 nm的红光,两个发射峰分别位于683 nm和694 nm,其最佳激发波长为590 nm。当原料中Al和B的量比为3.5时,样品的发光最强。初步分析了H3BO3的加入对样品发光影响的机理。样品的最佳煅烧温度为1 150℃。随着Cr3+掺杂浓度的升高,样品发光增强,但发光效率降低。样品的漫反射光谱表明,样品对绿光、黄橙光及紫外光有较强的吸收,是一种潜在的优良农用转光剂材料。     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Characterization of PolyA and PolyC mismatches by Raman spectroscopy

A.C mismatches are studied by Raman spectral characterization of PolyA, PolyC, and their equimolar complex in solution of 0.14 mol/L Na ,pH7.0.Experimental results show that A·C mismatches occur to be A/B (mainly A) conformers, and unlike Watson-Crick base pairing, this kind of mismatches is stabilized by only one hydrogen bond involving cytosine N4H2 and adenine N7.The formation of A·C complex makes the base stacking interactions much stronger, and conformation of the backbone more ordered, which leads to obvious Raman hypochromic effect with some shifts in corresponding bands.     

Improvement of four-wave mixing-based wavelength conversion efficiency in dispersion shifted fiber by 40-GHz clock pumping

40-GHz clock modulated signal as a pump to improve the efficiency of four-wave mixing (FWM)-based wavelength conversion in a 26.5-km dispersion shifted fiber (DSF) is investigated. The experimental results demonstrate that the conjugated FWM component has higher intensity with the clock pumping than that with the continuous-wave (CW) light pumping. The improvement of FWM-based wavelength conversion efficiency is negligible when the pump power is less than Brillouin threshold. But when the pump power is greater than Brillouin threshold, the improvement becomes significant and increases with the increment of pump power. The improvement can increase up to 9 dB if pump power reaches 17 dBm.     

Multi-pulse operation of a Kerr-lens mode-locked femtosecond laser

Our experimental results show that the presence of a proper amount of negative group velocity dispersion is essential to multi-pulse operation of a Kerr-lens mode-locked femtosecond laser. We demonstrate that the pulse separations and the number of pulses contained within a cavity round trip are strongly dependent on the initial perturbations. The results allow us to get a better understanding on the influences of the convoluted self-phase modulation and intra-cavity dispersions on the stable multi-pulse oscillation in a Kerr-lens mode-locked femtosecond laser.     

Propagation of Helmholtz-Gauss beams in weak turbulent atmosphere

Based on the Rytov approximation of light propagation in weak turbulent atmosphere,the closed-form expressions of field and average irradiance of each one of the four fundamental families of Helmholtz-Gauss (HzG)beams:cosine-Gauss beams,stationary Mathieu-Gauss beams,stationary parabolic-Gauss beams,and Bessel-Gauss beams,which are propagating in weak turbulent atmosphere,are obtained.The results show that the field and average irradiance can be written as the product of four factors:complex amplitude depending on the z-coordinate only,a Ganssian beam.a factor of complex phase perturbation induced by atmospheric turbulence,and a complex scaled version of the transverse shape of the non-diffracting beam.The effect of weak atmospheric turbulence on irradiance distribution of the HzG beam can be ignored.     

An effective method for reducing speckle noise in digital holography

An effective method for reducing the speckle noise in digital holography is proposed in this paper.Different from the methods based on classical filtering technique,it utilizes the multiple holograms which are generated by rotating the illuminating light continuously.The intensity images reconstructed by a series of holograms generated by rotating the illuminating light possess different speckle patterns.Hence by properly averaging the reconstructed intensity fields,the speckle noises can be reduced greatly.Experimental results show that the proposed method is simple and effective to reduce speckle noise in digital holography.     

Influence of purity of HfO2 on reflectance of ultraviolet multilayer

The impurities in two kinds of HfO2 materials and in their corresponding single layer thin films were determined through glow discharge mass spectrum technology and secondary ion mass spectrometry(SIMS) equipment respectively.It was found that ZrO2 was the main impurity in the two kinds of HfO2 either in the original HfO2 materials or in the electron beam deposited films.In addition,the difference of Zr content in the two kinds of HfO2 single laver films was much laxger than that of the other impurities such as Ti and Fe.which showed that it was just ZrO2 that made the difference between the optical performance of the film products including the two kinds of HfO2.With these two kinds of HfO2 and the same kind of SiO2.we deposited HfO2/SiO2 multilayer reflective coatings at the wavelength of 266 nm.Experimental results showed that the reflectances of these two mirrors were about 99.85% and 99.15% respectively,which agreed well with the designed results what were based on the optical constants obtained from the corresponding single layer thin films.     

Speech enhancement by array crosstalk resistant ANC and spectrum subtraction

Microphone array-based speech enhancement has great importance for speech communications and speech recognition. To reduce the aperture of the microphone array and to increase the effect of the speech enhancement will greatly broaden the application areas of the microphone array. An array crosstalk resistant adaptive noise cancellation method is therefore presented. And then an improved spectral subtraction algorithm is further cascaded to obtain better enhancement results. Theoretic analysis and experiments indicate that the proposed scheme needs only a very small microphone array while it simultaneously achieves a higher SNR improvement. Besides, the proposed scheme can be used in many noisy environments and is easy for real-time implementation.