氢等离子体气氛中退火多孔硅的表面和光荧光特性

用电化学腐蚀法制备了多孔硅(PS),在氢等离子体气氛中不同温度下对多孔硅样品进行了退火处理,并进行了光致发光(PL)谱和原子力显微镜(AFM)表面形貌的测量。不同退火温度给PS表面形态带来较大变化,也影响了其PL谱特性。在退火的样品中观察到的PL谱高效蓝光和紫光谱带,我们认为主要源于量子限制发光峰和非平衡载流子被带隙中浅杂质能级所俘获而引起的辐射复合所产生的。在420—450℃退火处理的多孔硅的PL谱上观察到了一个未见诸于报道的紫光新谱带(3．24eV,382nm),其发光机理有待于进一步研究。     

多孔硅锗的制备及其近红外发光增强

用激光照射辅助电化学刻蚀硅锗合金样品能够形成多种低维纳米结构。在硅锗合金上形成的多孔状结构在波长为725 nm处有很强的光致发光(PL)峰,PL的增强效应不能单独用量子受限模型来解释。我们提出新的模型来解释这种低维纳米结构的PL增强效应。     

激光照射下的低温氧化生成锗的纳米结构及其特性

在高精度椭偏仪（HPE）系统中，采用激光照射硅锗合金衬底助氧化的新方法，在SiO2层中生成锗的双纳米面结构；并在样品生长过程中，用HPE同步测量样品的纳米结构. 用Raman光谱仪测量样品的横断面，发现很强的PL发光谱峰. 用量子受限模型和改进的量子从头计算（UHFR）方法分析了PL光谱的结构. 关键词： 高精度椭偏仪 锗的纳米结构 PL光谱 量子受限     

激光辐照和高温氧化硅锗合金的低维结构和发光特性

采用强激光辐照硅锗合金,然后高温氧化的方法,在样品表面生成微米级小孔,用高精度扫描电镜观察孔内结构,发现片状纳米结构的存在。用荧光光谱仪测量其光致荧光谱,对于激光辐照(无高温氧化)的样品,在峰值705 nm处出现较强的光致发光(PL)。高温氧化后,样品在606 nm处出现一尖锐的PL光谱。利用量子受限和纳晶与氧化物的界面态综合模型解释PL光谱的产生。     

C(膜)/Si(SiO2)(纳米微粒)/C(膜) 的光致发光性质研究

用直流辉光溅射法结合真空镀膜法制备出了一种“多层三明治结构”的光致发光材料—C(膜 ) /Si(SiO2 ) (纳米微粒 ) /C(膜 )夹层膜 ,然后分别在 40 0、6 5 0和 75 0℃退火 1h .在波长为 2 5 0nm的紫外光激发下 ,刚制备出来未经退火处理的样品具有一个在 398nm (3.12eV)处的紫光宽带PL1峰 .在 6 5 0℃退火后 ,又出现了一个在 36 0nm (3.44eV)附近的PL2 峰 .PL1和PL2 峰形状和峰位与退火温度和激发波长无关 ,但强度却与退火温度和激发波长密切相关 .结合形态结构分析可知 ,紫光PL1峰可用量子限制 -发光中心 (QC LCs)模型进行解释 :即光激发发生在SiO2 微粒内部 ,而光发射源于SiO2 与Si界面上的缺陷中心 .紫外荧光PL2 峰则源自SiC内部的电子 空穴复合发光     

多孔硅量子点中的电子局域态

经过激光辐照和高温退火加工能够生成多孔硅样品,在650—780 nm处检测到很强的光致荧光（PL）峰,并且有明显的钉扎和增强效应.实验表明,这种PL发光的强度与样品受辐照和退火的时间短密切相关.通过第一性原理模拟计算发现,样品表面用SiO 双键和Si—O—Si桥键钝化,能隙中会出现电子局域态.激光辐照和高温退火的时间长短决定了样品表面SiO双键和Si—O—Si桥键的密度,而该密度正是影响多孔硅量子点中电子局域态生成的关键. 关键词： 多孔硅量子点 硅氧钝化键 电子局域态     

掺钛化学腐蚀法制备发光稳定的多孔硅

本文采用掺钛化学腐蚀法制备出了发光稳定性和均匀性都较好的多孔硅 (PS)。存放和退火试验表明 ,光致发光 (PL)谱峰位不蓝移 ,强度不衰减。多孔硅发光稳定性的提高归因于制备过程中样品表面原位氧和钛的钝化。钛的浓度和腐蚀时间对PL强度有明显影响 ,最佳钛浓度约为 0 0 8mol·L- 1 ,最佳腐蚀时间约为 2 0min。掺钛化学腐蚀法制备的PS的光激发过程符合量子限域机制 ,而其PL过程却与量子限域模型不符 ,这表明其光发射过程不是带 带直接跃迁产生的 ,即存在一个表面态     

多孔硅在30~180℃温区光致发光谱的研究

对长期存放在空气中的多孔硅样品和即时制备的多孔硅样品分别在室温~180℃下进行了光致发光（PL）温度效应的研究.两类样品的PL呈现不同的变化规律.前者的PL还表现为双峰,且长波PL峰随温度升高蓝移;后者的PL表现为单峰,且PL峰位随温度升高红移.基于量子限制效应对后者进行了解释;而前者难以用分立的量子限制和表面发光中心模型来解释,实验结果表明两种机制之间可能有较复杂的耦合效应发生.     

退火对ZnS/PS复合体系光致发光特性的影响

用脉冲激光沉积(PLD)技术以多孔硅(PS)为衬底生长了ZnS薄膜,分别测量了ZnS、PS以及ZnS/PS复合体系在室温下的光致发光(PL)光谱。结果发现,ZnS/PS复合体系的PL光谱中PS的发光峰位相对于新制备的PS有所蓝移。把该ZnS/PS样品分成三块,在真空400℃分别退火10,20,30 min,研究不同退火时间对ZnS/PS复合体系光致发光特性的影响。发现退火后样品的PL光谱中都出现了一个新的绿色发光带,归结为ZnS的缺陷中心发光。随着退火时间的延长,PS的发光强度逐渐降低且峰位红移。把ZnS的蓝、绿光与PS的红光相叠加,整个ZnS/PS复合体系在可见光区450~700 nm形成一个较宽的光致发光谱带,呈现较强的白光发射。     

多孔硅的制备条件对其光致发光特性的影响

不同的实验条件下制备的多孔硅的光致发光(PL)特性是不同的,这是许多研究产生分歧的主要原因。对比分析了阳极氧化电流密度、阳极氧化时间、溶液浓度以及自然氧化时间对多孔硅光致发光光谱的影响。认为在一定的范围内,多孔硅的发光峰位会随电流密度的增大而蓝移,要获得较强的发光,需要选择合适的电流密度;随着腐蚀时间的延长,多孔硅的发光峰位也发生蓝移。当HF酸的浓度较小时,峰位随浓度的增大表现为向低能移动;而当HF酸的浓度较大时,峰位随浓度的增大则表现为移向高能。多孔硅在空气中自然氧化,其发光峰位发生蓝移,而发射强度随放置时间的延长而降低。并用量子限制模型和发光中心模型对实验结果进行解释。     

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.