铷原子磁光阱中超冷等离子体的形成和演化（英文）

在铷原子的磁光阱中,通过光电离冷原子方法和稠密里德堡原子的自发演化方法产生了超冷等离子体.磁光阱中冷却并囚禁了10^7个原子,温度约为500μK,之后用一束脉冲激光将冷原子电离或者激发至高里德堡态,通过调节脉冲激光的能量控制离子数量或者里德堡原子的数量.利用延迟斜坡电场或脉冲电场引出超冷等离子体中的电子,对超冷等离子体的形成和演化进行了研究,并利用库仑势阱模型对实验结果进行了解释.实验结果表明,由于来自长寿命里德堡原子的贡献,里德堡原子自发演化形成的超冷等离子体的寿命比光电离形成的超冷等离子体的寿命长.     

铯47D精细能级超冷里德堡原子自由演化的动力学研究

用连续窄线宽激光器将超冷铯里德堡原子分别激发到47D_3/2, 47D_5/2精细态, 观察了处于里德堡精细态的铯原子向超冷铯等离子体自由演化的过程, 详细对比了不同精细态的铯里德堡原子预电离时间、电离速率以及等离子体的转化效率. 将里德堡原子快速转化为等离子体的过程解释为局域势阱内由预电离产生的电子与里德堡原子的快速碰撞导致的雪崩电离.     

大失谐连续输运激光情形下双磁光阱中冷原子的输运

在我们建立的铯原子双磁光阱实验装置上,采用连续激光将气室磁光阱中冷却并俘获的冷原子输运到超高真空磁光阱.在前期利用近共振弱光研究原子输运的工作基础上,我们将输运激光的负失谐量扩展到约2.0 GHz,并增大了输运光功率,对冷原子的输运作了实验研究.结果表明:在大负失谐情形下,较强的输运光使冷原子输运更为有效,归因于输运光束对原子的偶极力造成对冷原子的导引作用.     

紫外光诱导原子脱附技术在单腔磁阱装载中的应用

基于光诱导的原子脱附技术，采用脉冲紫外光剥离出玻璃池壁上吸附的铷原子以形成可快速开启和关断的脉冲铷原子源，成功地解决了单真空腔系统中磁阱的原子数和寿命之间的矛盾，突破了激光冷却和囚禁技术向小型化乃至微型化发展过程中的一个瓶颈.脉冲光源由390nm的LED阵列组成.实验结果表明它能够在1s内使真空铷原子气体分压提高近30倍,并且当紫外光关闭后系统的真空恢复到平衡状态的时间非常短，约120ms.测量了不同铷原子分压下磁光阱所俘获的最大原子数和装载时间,并由此得出系统的背景真空和磁光阱所能俘获的极限原子数，进一步得出磁阱的原子数-寿命积与磁光阱保持阶段时间的变化关系，结果显示在约1.25s处出现极大值，与无磁光阱保持阶段而直接进行磁阱装载情况相比提高了约0.3倍. 关键词： 激光冷却 磁光阱 光诱导原子脱附 原子数-寿命积     

Na原子高里德堡态的辐射寿命

用可调谐激光两步激发Ｎａ原子高激发发里德堡态布居，在光激发后施加脉冲电场测量激发态的场电离阈，利用阈值电场和延迟场电离方法测定了ｎｓ（ｎ＝２０～２４）和ｎｄ（ｎ＝１９～２３）态的寿命值，并与计算值进行了比较，对影响寿命的因素作了讨论。     

超冷里德堡原子的产生以及探测

利用激光冷却与俘获技术获得冷原子,由双光子激发产生超冷里德堡原子,利用场电离法得到了里德堡原子ns和nd态的离子谱图;再将激光波长固定在6p3/2-34d态的共振跃迁线上,得到了离子和里德堡原子的TOF(Time of Flight)图,并对实验结果做了分析.     

用吸收法对铯原子磁光阱中冷原子数目的测量

介绍了吸收法测量冷原子数的原理以及对铯原子气室磁光阱中俘获的冷原子数目的测量过程及结果. 与通常的荧光收集法相比，在原理上与静止二能级原子同共振单模光场作用的模型更加接近，同时大大减小了测量中的误差累积，提高了测量精度. 测得的冷原子数为(8±0.3)×10⁶，同时还利用测得的阱中俘获的稳态冷原子数和磁光阱中冷原子的寿命间接获得了磁光阱的俘获率. 关键词： 激光冷却与俘获 磁光阱 冷原子数目 俘获率     

基于振幅调制的超冷铯原子高分辨光缔合光谱的实验研究

基于振幅调制的超冷铯原子高分辨光谱的实验研究，用相对于铯分子6S_1/2+6P_3/2离解限红失谐的光缔合激光作用于磁光阱中超冷铯原子，观察到通过光缔合产生的激发态超冷分子.在实验中，为了得到高信号-噪声比的光缔合光谱，利用声光调制器对俘获光进行振幅调制，将探测到的超冷铯原子的荧光信号利用lock-in技术解调.同时利用密度矩阵方程系统地分析了实验结果.     

飞行时间质谱探测磁光阱中超冷分子离子的实验研究

利用飞行时间质谱探测了由磁光阱中的俘获光和 再泵浦光光缔合作用形成的超冷基态铯分子, 研究了微通道板工作电压、加速电场强度和加速电场持续时间对铯分子离子信号强度的影响. 实验结果与理论模型的拟合一致; 获得了适合实验条件的最优化实验参数, 为进一步研究超冷分子的光缔合光谱和光电离光谱奠定了实验基础.     

超低频调制光缔合光谱的实验研究

通过激光冷却技术在磁光阱中俘获原子数约107,温度约200 μK,直径约400 μm的超冷铯原子,利用超冷铯原子光缔合方法制备了激发态的超冷铯分子。实验研究了光缔合光不同扫描速率对铯分子振转光谱分辨率的影响,发现光缔合光扫描速率较慢时,铯分子振转光谱分辨率较高。通过高灵敏的雪崩光电探测器探测冷原子荧光,获得了超冷铯分子第一激发态6S_1/2+6P_3/2离解限0-_g长程态高分辨振转光谱。为了实现受控拉曼光缔合制备超冷基态分子,光缔合激光频率需要锁定在原子-分子共振跃迁线,对超冷原子光缔合光谱进行了超低频波长调制,通过改变调制幅度和调制频率获得最优化的一阶微分信号,将该信号反馈回激光器,实现闭合环路稳频,满足了受控拉曼光缔合制备振转能级可控的基态分子的实验要求,该工作对研究受限空间中的超冷原子分子具有很重要的意义。     

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.