通过绝热过程制备W态

提出一种方案制备W态,方案基于暗态绝热过程.制备过程中,所有原子都处于基态,光纤模保持在真空态,在一定条件下可以忽略腔场激发,因此,方案非常抗消相干.方案的另一个优点是:只要满足绝热条件,不必要精确调节相互作用时间.方案成功的几率随原子数的增加而增加.     

BBOⅠ类相位匹配光参量放大中群速失配的补偿

描述了在BBOⅠ类相位匹配的飞秒光参量放大（OPA）中，利用非共线结构和倾斜抽运光的脉 冲波面来完全补偿三波群速失配的方法.理论计算了三波群速匹配时，非共线角、相位匹配 角、抽运光的脉冲波面倾斜角随信号光波长的变化，并分析了对抽运光光斑尺寸的要求和对 空间走离长度的影响.结果表明，利用该方法不仅能够实现最大的参量带宽，而且能够完全 补偿飞秒OPA中三波的群速失配.此外，选取合适的抽运光光斑尺寸和非线性晶体的长度对提 高参量增益也至关重要. 关键词： 群速匹配 非共线相位匹配 脉冲波面倾斜 飞秒光参量放大     

Precise measurement of the line width of the photoassociation spectra of ultracold molecules by using a frequency shifter

We propose a technique to precisely measure the line width of the photoassociation spectra of the excited cesium molecule by using a frequency shifter to generate two laser beams with a precise frequency difference. A series of photoassociation (PA) spectra are recorded with two laser beam induced molecular lines, whose peak separation serves as an accurate frequency ruler to measure the line width of the PA spectra. The full width half maximum line width was studied as a function of PA laser intensity. The extrapolated value at zero laser intensity is (34.84 ± 0.22) MHz. By analyzing other broadening mechanisms, a value of (32.02 ± 0.70) MHz was deduced. It is shown that this scheme is inexpensive, simple, robust, and is promising for applications in a variety of other atomic species.     

On the boundary slip of fluid flow

For hundreds of years, in all the textbooks of classical fluid mechanics and lubrica- tion mechanics it is assumed that there was no wall slip (boundary slip) at a liquid-solid interface, i.e. no relative motion between liquid and solid at the interface. This is the no-slip boundary condition. It has been widely applied to engineering and experiments and to almost all the rheology or viscosity measurements of fluids. Rheology is one of the most important bases for fluid mechanics and lubricati…     

Thermal stability and photoluminescence property of hexagonal MoO3·0.55H2O microrods

The metastable phase of well-faceted, hexagonal, prism-like molybdenum oxide hydrate (MoO₃·0.55H₂O) was successfully synthesized by evaporating molybdic acid solution prepared through cation membrane electrolysis of Na₂MoO₄·2H₂O aqueous solution. The obtained crystals were characterized by X-ray diffraction (XRD), thermogravimetric (TG), scanning electronic microscopy (SEM) and photoluminescence (PL) spectrophotometry. The as-prepared MoO₃·0.55H₂O rods were of 2–4 μm in width and 5–12 μm in length. The MoO₃·0.55H₂O microrods displayed photoluminescence properties at room temperature and were transformed into stable orthorhombic α-MoO₃ after air annealing at 380 °C. Moreover, the influence of temperature factor on the phase transformation process, morphology and photoluminescence properties of MoO₃·0.55H₂O was investigated in detail.     

Ultrafast Saturable Absorption of Core/Shell Colloidal Quantum Dots

Ultrafast saturable absorption (SA) materials that are capable of blocking the optical absorption under strong excitation have extensive applications in photonic devices. This work presents core/shell colloidal quantum dots (CQDs) which have the quantized energy levels, excellent band gap tunability, and possess significant SA performance. When the band gap is close to the pump pulse energy, the CQDs show significant resonant SA response. At the same excitation conditions, the core/shell CQDs dispersions show better SA response than graphene dispersions, and comparable to the recently reported molybdenum disulfide. The carrier dynamics of the SA of the CQDs is analyzed systematically. The research has also found that the two‐photon absorption of the CQDs show nearly cubic power law of the band gap, while the SA performance keeps almost the same in the nonresonant regime. Further, superior passive Q‐switched laser behavior is observed using the CQDs as a saturable absorber. The results directly reveal the physical processes of this basic problem and broaden the applications of CQDs in photonic devices.     

Application of 3-D Fluorescence: Characterization of Natural Organic Matter in Natural Water and Water Purification Systems

Natural organic matter (NOM) found in water sources is broadly defined as a mixture of polyfunctional organic molecules, characterized by its complex structure and paramount influence on water quality. Because the inevitable release of pollutants into aquatic environments due to an ineffective control of industrial and agricultural pollution, the evaluation of the interaction of NOM with heavy metals, nanoparticles, organic pollutants and other pollutants in the aquatic environment, has greatly increased. Three-dimensional (3-D) fluorescence has the potential to reveal the interaction mechanisms between NOM and pollutants as well as the source of NOM pollution. In water purification engineering system, the 3-D fluorescence can indicate the variations of NOM composition and gives an effective prediction of water quality as well as the underline water purification mechanisms. Inadequately treated NOM is a cause of precursors of disinfection byproducts (DBPs), posing a potential threat to human health. Effective control and measurement/evaluation of NOM have long been an important factors in the prevention of water pollution. Overall, 3-D fluorescence allows for a rapid identification of organic components thus indicating possible sources of water pollution, mechanisms of pollutant interactions, and possible DBPs formed during conventional treatment of this water. This article reviews the 3-D fluorescence characteristics of NOM in natural water and typical water purification systems. The 3-D fluorescence was effective for indicating the variabilities in NOM composition and chemistry thus providing a better understanding of NOM in natural water system and water engineering system.     

用于CARS激发源的全光纤飞秒脉冲谱压缩

进行了基于光纤预啁啾和自相位调制的多模/单模组合式全光纤啁啾谱压缩研究.提出利用多模光纤模式估计群速度色散均值的方法,并将该估计值作为啁啾参量分析的计算参数,仿真计算了50/125μm折射率渐变多模光纤的群速度色散均值及其与单模光纤在不同长度比值下的光谱压缩效果.采用三种折射率渐变多模光纤进行实验,对比分析了折射率渐变多模光纤的芯径大小及其与单模光纤的长度比值对光谱压缩效果的影响.实验结果表明使用50/125μm折射率渐变多模光纤获得光谱最大压缩比为5.796,谱宽为2.243 nm,与理论仿真一致;使用105/125μm折射率渐变多模光纤,可进一步提高压缩比至152.941,输出谱宽为0.085 nm的光脉冲.将此脉冲用于相干反斯托克斯拉曼散射光谱探测,理论光谱分辨率可达1.386 cm~(-1).