■H自由基LIF光谱研究

利用脉冲高压直流放电技术产生■H超声分子束,以纳秒染料激光二倍频输出(282 nm)作为激发光源,通过LIF光谱测量方法,获得了O.HA2Σ+-X2Π(1,0)带转动分辨激发荧光谱,并通过对谱线强度分布的分析和计算,得到X2Π态O.H的转动温度为(30±1)K;通过对A2Σ+-X2Π(1,1)带及(0,0)带跃迁的荧光衰减时间谱测量,拟合得出O.H激发态A2Σ+(v′=1)及X2Π(v″=0)的寿命分别为(637±6)和(675±13)ns。     

硫化镍激光诱导荧光光谱：一个新的低激发态

采用激光诱导荧光技术在12200～13550 cm^-1能量范围内研究了超声射流冷却下的硫化镍光谱. 获得了4个具有转动结构的振转带,并被归属为基态至低激发态[12.4]³∑₀^- 的跃迁. 通过转动分析,确定了该低激发态的转动常数、同位素位移以及分子(平衡)常数. 此外,还测量了这些振转带的寿命.     

碰撞诱导振动能量转移：Cs2[B1∏u(v′=5)]+ N2→Cs2[B1∏u(v′=4，6)]+ N2

利用激光诱导荧光方法研究了Cs2[B1∏u(v′=5)]与N2的碰撞能量转移。脉冲激光激发Cs2基态至[B1∏u(v′=5)]态,池温保持在410K ,N2气压在1.5×102Pa至2.5×103Pa之间变化。荧光中含有直接荧光和碰撞转移荧光成分,记录直接荧光B1∏u(v′=5)→X1∑+g(v〞=0)的时间分辨强度。从荧光强度的对数值给出的直线斜率得到B1∏u(v′=5)→X1∑+g(v〞=0)的有效寿命,由Stern-Volmer方程,得到B1∏u(v′=5)→X1∑+g(v〞=0)的辐射寿命为（45±9）ns。B1∏u(v′=5)态与N2碰撞的猝灭总截面为（9.8±1.5）×10-15cm2。用类似的方法得到B1∏u(v′=4,6)能级的辐射寿命。在不同的N2气压下,测量B1∏u(v′=5,4,6)→X1∑+g(v〞=0)的时间积分荧光强度,首次得到v′=5→v′=4及v′=5→v′=6的碰撞转移截面分别为(3.9±0.8)×10-15cm2和(4.1±0.8)×10-15cm2。     

弯曲振动对CS_2分子~1B_2(~1Σ_u~+)态预解离寿命的影响

在209.5～216nm,采用光解碎片激发(PHOFEX)谱技术,对CS2分子1B2(1Σ+u)态预解离寿命进行了 考察.测量在超声射流中进行.信号来自解离碎片CS(A1Π,v′=0←X1Σ+,v″=0)Q支带头的激光诱导荧光 (LIF).预解离寿命是通过对谱带进行拟合来提取的.拟合中假定基态转动布居为Boltzmann分布,寿命加宽的转 动谱线为Lorentz线形.通过拟合共获得1B2(1Σ+u)态13个跃迁所对应的预解离寿命,其中6个数据是新得到的. 结果表明,基态振动角动量量子数l或激发态转动角量子数K(K=l)对预解离寿命有明显的影响.对于激发态的 同一振动能级,较大的K对应于较短的预解离寿命.实验中采用可加热的射流喷嘴,用以提高热带激发的强度, 以改善对较大转动角量子数K的影响的考察.     

氧化镍位于510～610 nm的激光诱导荧光光谱 (cited: 1)

采用激光诱导荧光技术在510～650 nm研究了超声射流冷却下的氧化镍光谱,观测了55个振转谱带. 通过转动分析发现激发态的同位素位移、振转间隔和转动常数都表现出高度的不规则性,26个[Ω=0,1]-X³∑^-₀的跃迁谱带被暂时归属为5个振动序列. 此外实验中还观测了部分谱带的色散谱和寿命.     

CsH(X1∑+,v≥15)与CO2碰撞中的振动-转动能量转移

研究了高位振动激发态CsH(v"=15～21)与CO2振动-转动碰撞转移过程.脉冲激光激发CsH至高振动态,利用激光感生荧光光谱(LIF)得到CsH(v")与CO2的猝灭速率系数kv"(CO2),kv"＝21(CO2)＝7kv"＝15(CO2).研究了CsH(v")+H2的弛豫过程,有kv"(H2)＞kv"(CQ),碰撞弛豫速率系数的质量效应明显.利用激光泛频光谱技术,测量了CO2(00°0)的转动态分布.对于CO2与CsH(v"=15)碰撞,CQ2有转动温度Trot=(605±50)K;对于v"=21,Trot=(780±70)K.基于转动温度,得到CO2的平均转动能〈Erot〉和转动能的变化〈ΔErot〉,发现〈ΔErot〉v"=21～2.7〈△Erot〉v"=15.由对CO2转动能级受激吸收线轮廓测量,得到J=36～48各能级的平均平动能〈Etel〉,对于v"＝15,〈Erel〉＝600～972 cm-1;对于v"=21,〈Erel〉=972～1351cm-1.低J值有低平动能.外推平动能到初始平动能520 cm-1(池温500 K的平动能)对于v"＝15和v"＝21,分别得到阈值Jth =34和24.大于初始平动能的转动态均处于Jth值之上.     

激光烧蚀Al热原子与CF4,CCl4,CH2Br2反应中激发态C2的形成

脉冲激光烧蚀平面铝靶产生的热原子与气相CF4,CCl4,CH2Br2的碰撞反应中,在430～600nm之间观测到激发态C2分子的发光光谱,它们可归属为Swan带的d^3Ⅱg=a^3Ⅱu跃迁中△v=2,1,0,-1,-2五个振动序列(v′≤6)。谱强度分析表明,C2激发态可很好的用热平衡描述,其振动温度达6000K左右。同时在△v=0和-1的振动带间观测到振荡的谱峰,它们是转动谱线叠加的结果。激光烧蚀Al产生的等离子体在膨胀中产生的激波及其本身的动能与反应气体碰撞使其解离产生C,然后复合形成C2。C2激发态d可能是通过激发态的Al(^2S)经近共振传能产生,也不排除在有足够碰撞能下优先形成C2激发态b,再通过与d态的v′=6能级交叉无辐射跃迁而进入d态。     

MgH的A2Π-X2Σ+振动跃迁的Frank-Condon因子和带头

利用激光消融/激光诱导荧光的方法测量了MgH分子A²Π～X²Σ⁺的色散荧光谱, 并通过分析实验光谱获得了MgH分子的A²Π(v′=0)～X²Σ⁺(v〞=0,1)跃迁的弗朗克-康登因子和相应的跃迁频率. 同时也用理论计算方法计算出MgH分子A²Π(v′=0)～X²Σ⁺(v〞=0,1)的弗朗克-康登因子和跃迁频率. 实验结果、理论结果和其他文献中的理论结果是一致的.     

CO三重带系d^3Δ-α^3∏（4，0）和（5，0）带激光光谱研究

光外差磁旋转浓度调制激光光谱技术属于一种高灵敏度的吸收光谱测量方法，可以用于瞬态分子和激发态分子光谱的检测。采用这种技术分别在16400～16650cm^-1和17450～17750cm^-1波段内直接观测到CO三重带系d^3△←α^3∏(4，0)(5，0)振转吸收光谱。这种跃迁的上态d^3△1(v=4)，d^3△2(v=4)，d^3△1(v=5)分别与A^1∏(v=0)，D^1△(v=0)和A^1∏（v=1)态存在微扰相互作用。通过对所测量到的CO三重带系(4，0)(5，0)振转谱带作了包含微扰相互作用在内的分析，获得了上态d^3△(v=4，5)的精确的分子转动光谱常数。     

CO三重带系d3Δ-a3Π(4,0)和(5,0)带激光光谱研究

光外差磁旋转浓度调制激光光谱技术属于一种高灵敏度的吸收光谱测量方法 ,可以用于瞬态分子和激发态分子光谱的检测。采用这种技术分别在 16 4 0 0～ 16 6 5 0cm-1和 174 5 0～ 1775 0cm-1波段内直接观测到CO三重带系d3 Δ←a3 Π(4,0 ) (5 ,0 )振转吸收光谱。这种跃迁的上态d3 Δ1(v =4 ) ,d3 Δ2 (v =4 ) ,d3 Δ1(v =5 )分别与A1Π(v =0 ) ,D1Δ(v =0 )和A1Π(v =1)态存在微扰相互作用。通过对所测量到的 CO三重带系 (4,0 ) (5 ,0 )振转谱带作了包含微扰相互作用在内的分析 ,获得了上态d3 Δ(v =4 ,5 )的精确的分子转动光谱常数。     

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.     

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.     

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.