Extending the trapping lifetime of single atom in a microscopic far-off-resonance optical dipole trap

In our experiment, a single cesium atom prepared in a large-magnetic-gradient magneto–optical trap (MOT) can be efficiently transferred into a 1064-nm far-off-resonance microscopic optical dipole trap (FORT). The efficient transfer of the single atom between the two traps is used to determine the trapping lifetime and the effective temperature of the single atom in FORT. The typical trapping lifetime has been improved from ～ 6.9 s to ～ 130 s by decreasing the background pressure from ～ 1 × 10^–10 Torr to ～ 2 × 10^–11Torr and applying one-shot 10-ms laser cooling phase. We also theoretically investigate the dependence of trapping lifetimes of a single atom in a FORT on trap parameters based on the FORT beam’s intensity noise induced heating. Numerical simulations show that the heating depends on the FORT beam’s waist size and the trap depth. The trapping time can be predicted based on effective temperature measurement of a single atom in the FORT and the intensity noise spectra of the FORT beam. These experimental results are found to be in agreement with the predictions of the heating model.     

强场下的Li-like氖复合机制X光激光的数值模拟

论述了隧道电离和阈上电离加热过程。并把此二过程加到一个non-LTE平均原子模型,用此模型来研究强场下光致电离类锂氖复合机制X射线激光。计算结果表明,当驱动激光脉冲为100fs、波长为0.248μm、功率密度为2×10¹⁷Wcm^-2,氖气的密度为10^-3gcm^-3时,类锂氖精细结构跃迁3d_5/2→2p_3/2(λ=98Å)的最大增益系数约为100cm^-1,其维持时间约为1.5ps。     

A cold thermionically emitting dusty air plasma formed by radiativeheating of graphite particulates

Formation of an atmospheric pressure dusty air plasma is explored experimentally in this paper. The plasma is created by seeding an air flow with graphite particles and irradiating the particulates with a focused CO₂ laser beam. The graphite particles are, thus, heated to thermionically emitting temperatures, and average particle temperatures and average particle number densities are measured. The presence of charges is inferred both from these measured quantities using a simple theoretical transient model, and experimentally by applying a dc bias across the irradiated region. It is found that an electron density of ~6.7 × 10⁵ cm^-3 (6.7 × 10¹¹ m^-3) can be produced at steady state in the presence of O₂. This value can be increased to 3.6 × 10⁷ cm^-3 (3.6 × 10¹³ m ^-1) in the ideal case where an electron attachment to O₂ is suppressed and where a lower work function particulate is used     

基于光强与吸收率非线性同步拟合的吸收光谱测量方法

针对高压环境吸收谱线加宽以及波分复用技术合波透射信号分析测试难题,提出利用非线性拟合方法对激光吸收光谱测量中激光强度与吸收光谱进行耦合求解.建立激光强度非线性变化与多谱线吸收拟合函数关系,解决了特殊环境下无法获取光谱基线的难题,实现了波分复用过程合波后光谱信号的分离与诊断.通过仿真验证该方法的可行性,分析计算了激光器特性和特征谱线位置等因素对拟合结果的影响.搭建实验台实现了1—10 atm变压力环境下6330—6337 cm~(-1)波段CO_2吸收光谱叠加信号的诊断分析,对气液两相脉冲爆轰过程中7185.6 cm~(-1)与7444.35 cm~(-1)波段波分复用光谱信号进行测试与拟合,无需分光设备实现了耦合光路分离和温度计算,研究结果对激光吸收光谱技术在高压环境以及燃烧环境下波分复用技术的发展具有重要意义.     

Multiphoton double ionization of barium

The multiphoton double ionization of Ba from ~280 to 700 nm was investigated using laser pulses 5 ns long of peak intensity ~10¹⁰ W/cm². The spectrum consists of a number of strong resonances, which can be assigned to Ba⁺ transitions. Most of the assignments have been verified by pump-probe techniques. Thus, the Ba⁺⁺ observed is due to sequential ionization. The multiphoton ionization probability is highest for λ~500 nm, which matches a series of strong Ba and Ba⁺ transitions leading to double ionization     

利用Er3+光学温度传感特性研究Tm3+/Yb3+掺杂NaY(WO4)2微米球的激光辐照热效应

采用微波水热方法合成了Er³⁺/Yb³⁺及Tm³⁺/Yb³⁺两个共掺杂的绣球花状NaY（WO₄）₂微米球样品。XRD结果表明所获得的产物为纯相体心结构的NaY（WO₄）₂,利用SEM观察发现产物粒子结构为纳米片组装成的绣球花状。考虑到红外激光辐照对样品产生加热效应,采用380 nm激发下不同温度的发射光谱获得了Er³⁺/Yb³⁺共掺杂NaY（WO₄）₂微米球的温度传感特性曲线和灵敏度曲线。把Er³⁺/Yb³⁺共掺杂NaY（WO₄）₂与Tm³⁺/Yb³⁺共掺杂的NaY（WO₄）₂按质量比1：10进行混合,采用980 nm激发测量了混合物的上转换发光光谱,研究了激光持续辐照对Tm³⁺/Yb³⁺掺杂NaY（WO₄）₂样品的加热效应和Tm³⁺的¹G₄→³H₆ 跃迁发光强度随激光辐照时间的变化。实验发现980 nm激光辐照使Tm³⁺/Yb³⁺掺杂NaY（WO₄）₂样品的温度持续升高并达到某一平衡温度,Tm³⁺的蓝色上转换发光也随着激光辐照时间的延长而增强,最后达到饱和。此外,在相同条件下,Tm³⁺/Yb³⁺共掺杂样品的激光辐照热效应比Er³⁺/Yb³⁺共掺杂样品的热效应更为显著。     

Flashboard plasma characterization using spectroscopy

The plasma produced by a 10 cm×6 cm planar flashboard has been investigated by emission spectroscopy. The plasma composition, density, and temperature have been determined with time and space resolution using measurement of the relative intensity of spontaneous emission in different atomic and ionic transitions together with calculations based on a collisional-radiative equilibrium model. The (1-2)×10¹³ cm^-3 and (3-4) eV plasma flows away from the flashboard surface at a speed of about 10 cm/μs. A 1.7 cm/μs transverse velocity has been obtained from the Doppler width of an emission line     

Yb :YAG晶体的闪烁特性

通过不同Yb³⁺掺杂浓度(5%~30%,原子数分数)的Yb:YAG晶体的阴极射线发光谱、衰减时间、光输出及其温度依赖关系的测量,研究了Yb:YAG晶体的闪烁性能.不同Yb³⁺掺杂浓度的Yb:YAG晶体具有不同的光输出和猝灭温度,光输出随Yb³⁺掺杂浓度的增大而降低,猝灭温度则随掺杂浓度的增大而升高.室温下Yb:YAG晶体的发光衰减时间较短,均小于50ns.Yb³⁺掺杂浓度为5%的Yb:YAG晶体具有较高的光输出和较低的猝灭温度.     

120TW/30fs激光产生的Al等离子体X射线发射谱分析

在SILEX激光装置上利用超强超短激光(120TW/30fs)与Al靶相互作用产生热稠密等离子体.采用类氢共振线与类氦共振线线强比诊断得到电子温度在480～670eV之间,采用类锂jkl伴线与类氦共振线强度比得到电子温度在430～610eV之间,两种诊断方法得到的结果基本一致.用类氦互组合线与类氦共振线强度比方法获得电...     

Dy^(3+)掺杂Lu_(2)O_(3)和Y_(2)O_(3)单晶光纤下转换荧光测温性能EI北大核心CSCD

稀土倍半氧化物单晶光纤材料凭借超高的熔点(~2400℃)、稳定的物化性能以及灵活的结构被认为是极具潜力的高温传感介质。本文采用激光加热基座(LHPG)法,成功生长了透明无开裂Dy^(3+)离子掺杂的倍半氧化物单晶光纤Lu_(2)O_(3)和Y_(2)O_(3)。依据Dy^(3+)离子的^(4)I_(15/2)和^(4)F_(9/2)能级为一对热耦合能级对(TCLs),测试得到了430~520 nm波长范围内的下转换荧光光谱。荧光强度比(FIR)结果显示,晶体在298~673 K温度范围内的荧光强度具有良好的温度相关性。其中Dy∶Lu_(2)O_(3)在该范围内的最大相对灵敏度和绝对灵敏度分别为0.97%·K^(-1)(315 K)和1.62×10^(-4) K^(-1)(673 K),展现出更为优异的温度传感性能。     

锶原子互组跃迁谱的实验研究

观测了热原子束中锶原子(5s²)¹S₀—(5s5p)³P₁ 互组跃迁的荧光谱和饱和荧光谱, 实验测定了不同的参量下 ⁸⁸Sr(5s²)¹S₀—(5s5p)³P₁ 互组跃迁荧光谱. 研究结果表明: 不同的实验参数(温度、激光光强、激光扫描频率)对谱线有较大的影响, (5s5p)³P₁态的长寿命特点导致谱线强度随激光扫描频率呈倒数关系变化; 由于Doppler增宽, 渡越增宽等因素的影响, 谱线线宽远大于其自然线宽且随激光扫描频率呈正比关系变化.     

The current density and the specific energy input in fastelectrical explosion

The electrical explosion of wires is considered as a method for studying the behavior of materials under the conditions of fast heating. A fast electrical explosion occurs subject to the conditions that the heating time is shorter than the time required for capillary and magnetohydrodynamic instabilities to develop and that this time is longer than the time required for the current to expand throughout the wire cross section. Corresponding similarity criteria have been derived for each of the processes disturbing the uniform heating of a wire. The conditions for fast electrical explosion have been experimentally realized. The current density was varied from 10⁷-10⁹ A/cm² resulting in heating rates between 10¹⁰ and 10¹³ J/(g.s). Exploded wires of copper, nickel, tungsten, and molybdenum were investigated. These experiments have shown that the energy density introduced into the wire material depends on the heating rate (i.e., the current density). Fourfold overheating of the materials in the condensed state has been attained. It has been found that the specific current action also increases with increasing current density but to a lesser degree than the energy input     

Absolute spectral distribution of soft X-ray emission from laserproduced gold plasma

Quantitative measurement of spectral distribution of soft X-ray emission from laser produced plasmas and estimation of X-ray conversion efficiency are reported. The X-ray emission from planar gold target irradiated by an Nd:glass laser was recorded using a high resolution transmission grating spectrograph. Spectral distribution of X-ray intensity was derived using calibrated film data and a deconvolution procedure to account for contribution of higher diffraction orders. Results of conversion efficiency per unit solid angle, at a laser intensity of ~4×10¹² W/cm² (λ_L = 1.054 μm), for 10< λ <80 Å and in the water window spectral region (23< λ< 44 Å) are presented. A three-fold increase in conversion efficiency was observed for second harmonic laser irradiation (λ_L = 0.527 μm) at an intensity of 8×10¹² W/cm²     

MgAl2O4:Mn2+绿色荧光粉的合成与光学性质

采用高温固相反应法制备了一系列MgAl₂O₄∶xMn²⁺。在450 nm的蓝光激发下,观察到了Mn²⁺的⁴T₁→⁶A₁跃迁的绿色发光,发射光在x=10%时达到最大值。研究结果表明,在x＞10%之后,材料的发光强度没有明显减弱。发光强度的减弱是由于Mn²⁺导致的缺陷增多引起的。缺陷态与Mn²⁺对于蓝色激发光进行竞争,并且对520 nm的发射光有再吸收过程。温度升高后的发光增强也被观察到。通过变温漫反射谱研究,我们认为这与充当电子陷阱的缺陷态在高温下内部电子被热激发有关。     

Ba5(PO4)3Cl：Eu2+荧光粉的制备和发光性能研究

以Eu₂O₃、NH₄H₂PO₄、BaCl₂·2H₂O、BaCO₃为原料,用高温固相法制备出Ba₅（PO₄）₃Cl：Eu²⁺荧光粉。用XRD衍射仪和荧光分光光度计分别测试样品的物相结构和荧光性能。结果表明：制备得到的Ba₅（PO₄）₃Cl：Eu²⁺为单相,在245~425 nm范围均有较大吸收,具有最强峰在435 nm的窄带发射。该荧光粉的发光强度受Eu²⁺浓度的影响较大,其发光随着Eu²⁺浓度的增加先增强后减弱。当Eu²⁺摩尔分数为3%时,发光强度达到最大。     

助熔剂BaF2在制备BaSi2O5:Pb2+过程中的机理

采用高温固相合成法制备出BaSi₂O₅:Pb²⁺荧光体。考察了BaF₂的加入量对产物紫外发射强度的影响。用差示扫描量热分析,X射线衍射,光致发光光谱研究了掺入助熔剂BaF₂后BaSi₂O₅:Pb²⁺紫外发射强度显著增强的机理,并从热力学角度对实验结果作了分析。研究表明少量BaF₂的掺入加快了反应速度;降低了BaSi₂O₅:Pb²⁺形成温度,在高温下与SiO₂反应生成SiF₄气体,生成的SiF₄再与BaCO₃反应形成结晶良好的BaSi₂O₅:Pb²⁺荧光体。     

毛细管放电类氖氩69.8nm激光增益特性研究

建立了计算69.8nm激光增益系数的理论模型,根据实验参数,计算了在主脉冲电流为12 kA时,69.8nm激光增益系数最大值为0.32 cm~(-1).理论模拟了不同初始气压下增益系数在毛细管径向上的分布情况.对理论结果的分析表明,最佳的初始气压在12—14 Pa范围内,此时69.8nm激光增益系数的极值最大.实验上,利用毛细管放电装置和罗兰光谱仪,测量了不同气压下的69.8nm激光强度,实验确定的最佳气压为16 Pa,与理论结果相近.此外,实验测量的增益系数(0.4 cm~(-1))略高于理论计算的增益系数(0.32 cm~(-1)).     

激光辐照VO2薄膜温度场分布及透射特性研究

为了探究VO₂薄膜受激光辐照的温度场分布,以及1 064 nm激光直接辐照100 s内至相变的激光功率密度阈值,并比较近红外和中红外波段透过率调制特性差异。首先基于COMSOL建立了薄膜受激光辐照的模型并进行了温度场仿真,然后分别测试了薄膜正反面被不同功率密度的1 064 nm激光辐照100 s内激光透过率随时间响应特性。实验中的VO₂薄膜利用分子束外延法在Al₂O₃基底上制备得到。仿真结果表明,激光功率密度为25 W·mm^-2时,50 nm厚薄膜在被辐照1 ms时间内即达到相变温度。经激光辐照实验发现:50 nm厚的VO₂薄膜正反面受1 064 nm激光直接辐照100 s内至相变的功率密度阈值分别为4.1 W·mm^-2和5.39 W·mm^-2。30 nm厚VO₂薄膜对1 064 nmn激光的透过率调制深度约为13%,对3 459 nm激光透过率调制深度约62%,说明VO₂薄膜对近红外透过率调制特性不明显。     

基于表面等离激元场的分子反射镜的理论研究

本文提出了一种基于微纳金属膜结构激发的表面等离激元场的分子反射镜新方案,利用中性分子与金属表面垂直方向上蓝失谐消逝波光场之间的偶极力相互作用,实现入射分子束的表面反射.理论计算了表面等离激元场的空间分布,用蒙特卡洛方法模拟了分子在该场中运动的动力学过程,得到了分子反射镜的反射率与相互作用时间和入射光强之间的关系.结果表明:当入射激光脉宽为10 ns,光强为I=1.0×109W/cm2时,纵向温度为10 mK,横向温度为1 mK的碘分子束反射效率达到55.89%,而且反射率随着入射光强的增大而增大.     

Tm$lt;sup$gt;3+$lt;/sup$gt;掺杂锗碲酸盐玻璃的近2 μm光谱性质

用高温熔融法制备了Tm₂O₃掺杂浓度为0.25, 0.5, 0.75, 1, 1.25, 1.5 mol%的40 GeO₂-35TeO₂-15PbO-5Al₂O₃-2.5CaO-2.5SrO锗碲酸盐玻璃. 热学性质测试表明该玻璃的转变温度为446 ℃, 没有析晶峰. 玻璃的最大声子能量约为750 cm^-1. 利用Judd-Ofelt 理论计算了Tm³⁺ 的Judd-Ofelt 参数Ω_t(t = 2, 4, 6)、不同浓度下Tm³⁺ 离子各激发态能级的自发辐射几率、荧光分支比以及辐射寿命等参数. 采用808 nm 波长抽运源测试了Tm³⁺ 离子的荧光光谱. 发现掺杂浓度为1 mol% 时约1.8 μm 处的荧光强度最强. 根据McCumber 理论计算了³F₄ →³H₆ 的发射截面, 其峰值发射截面为6.5 × 10^-21 cm². 根据速率方程计算了玻璃中OH 引起的Tm³⁺ 的³F₄ 能级的无辐射弛豫速率, 随着Tm³⁺ 浓度增加, OH 对³F₄ 能级的猝灭速率增加. 这种玻璃有望研制成一种新型的约2 μm 的激光玻璃材料. 关键词： 锗碲酸盐玻璃 3+掺杂')" href="#">Tm³⁺掺杂 光谱性质