用激光感生荧光法测量亚稳态原子寿命

本文用激光感生荧光法(LIF)分析了Gd原子亚稳态能级215cm~(-1),533cm~(-1),999cm~(-1)在原子束中的速度分布。由原子束轴线上两不同点上的亚稳态原子速度分布的变化得到了亚稳态原子的寿命。理论分析和实验结果表明这是一种简单、灵敏并且有效的亚稳态原子寿命测量方法。     

利用飞行时间法测定锶原子5s5p3P1亚稳态能级寿命

本文结合TOF法和吸收光谱测量技术,利用连续光场测定了锶原子亚稳态能级的寿命。实验中,利用689nm激光连续泵浦基态锶原子至5s5p3P1亚稳态能级,然后在距泵浦区域不同距离处观测处于5s5p3P1态的原子对688nm探测光的吸收强度,得到锶原子5s5p3P1态的能级寿命,我们利用TOF法实验得到的能级寿命为21.9±0.8μs。本文给出的方法具备实验装置简单的优点,同时可获得较高的测量精度。     

第一性原理研究SinB(n=1～12)团簇的稳定性

基于密度泛函理论(DFT),我们研究了SinB(n=1～12)团簇的稳定性.结果表明:SinB的基态构型是在Sin-1B的基态或亚稳态构型上带帽一个Si原子而得到;随着团簇尺寸的增大,B原子逐渐从吸附在Sin团簇的表面位置移动到Sin团簇笼内;掺杂B原子提高了纯硅团簇的稳定性;电子总是从Si向B转移,B原子所带的电荷数不仅与B原子的配位数有关,还与SinB团簇的基态结构密切相关.     

氦气空心阴极放电动力学过程的模拟研究

利用流体模型模拟研究了氦气空心阴极放电的时空动力学过程,计算得到了不同放电时刻电子和亚稳态氦原子密度、电势、电场、基态电离速率和分步电离速率等的时空分布特性。特别是讨论了亚稳态原子和分步电离对于放电的影响。结果表明,随着电流的增长,放电处于五个不同的放电模式:第一阶段电流上升非常缓慢,为汤生放电模式,带电粒子密度、亚稳态原子密度和径向电场均很弱;第二阶段电流迅速上升,放电模式由汤生放电向空心阴极放电过渡,带电粒子密度、亚稳态原子密度和径向电场迅速增强;第三阶段达到准稳态阶段,放电电流增长速度变缓,形成了明显的阴极鞘层结构;第四阶段为空心阴极效应形成阶段,向稳态阶段过渡;第五阶段为稳态放电阶段。研究结果同时表明,亚稳态氦原子和分步电离在放电的初始阶段对于放电的发展作用较弱,在前三阶段中,电子的产生以基态电离为主。随着放电的发展,由亚稳态原子引起的分步电离对新的电子产生的作用逐渐接近并超过基态电离,对总电离的贡献率越来越高。     

修正F-H实验中的氩原子第一激发电位

在F-H实验中可知,运动电子的动能大于11．8eV时,即可与氩原子发生非弹性碰撞,使氩原子的电子从基态受激跃迁到亚稳态。通过F-H实验的数据处理和对现代量子光学理论的分析,证实了氩原子存在亚稳态,并且修正了F-H实验中氩原子的第一激发电位。     

WnSi02,±(n=1～5)团簇结构与光谱的理论研究

利用密度泛函理论(DFT)在B3LYP/Lanl2dz水平上对WnSi0,2±(n=1～5)团簇的各种可能构型进行了几何结构优化,预测了各团簇的基态结构.并对基态构型的平均结合能、能隙、红外光谱及拉曼光谱进行了系统的理论分析.结果表明:WnSi0,2±(n=2～5)团簇的基态结构及亚稳态结构中的Si-Si原子不成键,W5Si0,2±团簇的基态构型与W7团簇的基态构型相似,W3Si2+团簇的基态构型与W0,5±团簇的基态构型相似;W5Si2-团簇是比较理想的复合材料;WnSi0,2±(n=1～5)团簇的所有IR吸收峰都属于红外光谱中的指纹区的特征吸收区域;除W4Si2-团簇外,其它团簇都具有非刚性特性.     

Von±(n=0,1,2)的势能函数与光谱常数研究

用密度泛函B3LYP/6-311++G(d,p)方法和相对论有效实势(Lanl2dz基组)对Von±(n=0,1,2)分子离子的势能函数及光谱常数进行了分析.结果表明它们都能稳定存在,其基态电子状态分别是:4Σ(VO2-),3Σ(VO-),4Σ(VO),3Σ(VO+)和2Σ(VO2+).其中VO2-和VO2+的势能函数曲线呈"火山口"型, 属于亚稳态分子离子.用七参数Murell-Sorbie势拟合VO2-和VO2+分子亚稳态双原子分子离子势能函数,发现其拟合曲线与势能函数曲线符合得很好.同时,讨论了电荷对势能函数和能级的影响.     

铥原子中等能量能级自然辐射寿命的时间分辨荧光测量

报道铥(Tm)原子10个中等能量激发能级自然辐射寿命的实验测量值.采用两台脉冲染料激光器将铥原子从基态激发到待测能级,再从铥原子激发态所释放的荧光随时间衰变的规律推算出自然辐射寿命值.测量精确度为10％.     

ZnH~(n±)(n=0,1,2)双原子分子离子光谱与分析势能函数研究

用密度泛函B3LYP/6-311++g(d,p)方法对ZnH~(n+)(n=0,1,2)分子离子的势能函数及光谱常数进行了分析,结果表明0价和±1价分子离子都能稳定存在而±2价离子有亚稳定态存在,其基态电子态分别为~2∑(ZnH),~1∑(ZnH~+),~1∑(ZnH~-),~2∑(ZnH~(2+)),~2∑(ZnH~(2-)),其中±2价离子的势能函数曲线明显呈"火山口"型,属于亚稳态分子离子,用八参数Murrell-Sorbie势拟合±2价亚稳态双原子分子离子势能函数得到的拟合曲线与势能扫描点符合得非常好,而四参数Murrell-Sorbie势对±2价离子的拟合与势能扫描点有较大的差距.     

气体激光激励过程与新激光器的研究

一、气体激光的微观过程1.能量共振转移碰撞过程 氦氖激光是由氦亚稳态原子与氖基态原子能量共振转移碰撞,引起对激光上能级的泵浦,形成集居数反转状态. 前一过程产生6328埃(3S2-2P4)和3.39微米(3S2-3P4)激光,后一过程产生1.15微米(2S2-2P4)激光.这两过程相应的能级差小于0.1电子伏特,都满足能量共振条件.式下的箭头表示电子自旋趋向,过程(1)满足维格勒自旋守恒定则(WSR),不引起电子自旋趋向的变化.过程(2)引起电子自旋趋向的变化,不满足WSR.因此,过程(1)的截面大于过程〔2).有人用脉冲余辉法测量了氦亚稳态消激发过程的总截面,但不能…     

Non-Maxwellian anisotropic velocity distribution of metastable argon atoms in a thin discharge cell

For an argon glow discharge in a 1 mm thick cell at room temperature, we have observed the absorption spectrum of the 1s₃–2p₂ (Paschen notation) line by using a diode laser. It is found that, with a decrease in the gas pressure below 0.1 Torr, the linewidth drastically decreases; at 0.02 Torr the velocity distribution of the metastable atoms in the surface normal direction has an apparent temperature of 144 K. The velocity distribution is also found to be anisotropic: the spectrum profile depends on the direction of observation with respect to the surface normal. These phenomena are explained by a model in which the velocity distribution of the metastable atoms is controlled by collisional quenching at the wall surface and velocity-changing collisions with ground state atoms.     

利用激光冷却原子束测量氦原子精密光谱

⁴He原子2³S₁→2³P_0,1,2跃迁的精细结构分裂,目前在理论和实验上都能够达到10^-8水平的精度,并可被应用于测定精细结构常数α, 和对量子电动力学进行检验.该方面实验研究的关键, 是需要提高测量信噪比,并消除各种可能的系统偏差, 将这一精细结构分裂测量到亚kHz水平.在设计的这套实验方案中, 首次结合激光冷却原子技术,通过激光横向冷却来提高亚稳态氦原子束的束流强度,并对三态亚稳态氦原子进行偏折, 将其从原子束中分离,从而大幅降低测量背景,并利用频率锁定激光器的边带扫描的方式来进行光谱测量,以使得扫描测量中保持足够的频率精度. 在目前基本搭建成的实验装置上,实验方法的可行性已经获得验证,分析表明有望实现亚千赫兹水平的测量准确度.     

半导体泵浦射流型亚稳态氩激光国际首次出光北大核心CSCD

半导体泵浦亚稳态惰性原子激光是高能光泵浦气体激光领域具有潜力的新方案。已有报道均在约束的放电空间内产生亚稳态原子,功率放大受到多因素制约。为突破现有方案的局限,采用大气压等离子体射流方式在羽流区域产生高浓度亚稳态氩原子(1014 cm^(−3)量级),将放电和激光区域空间分离,利用811 nm窄线宽半导体激光器作为泵浦源,基于泵浦、激光和气流相互垂直的结构实现912 nm激光输出,有效拓展了该型激光体系的功率定标放大能力。     

Single-pulse collision-insensitive picosecond planar laser-induced fluorescence of OHA 2 Σ + (v′ = 2) in atmospheric-pressure flames

Single-pulse two-dimensional picosecond Laser-Induced Fluorescence (LIF) imaging of the OH density in a single quantum state was performed for the first time, using a premixed methane-oxygen flame at atmospheric pressure. A picosecond, excimer-Raman-laser system (268 nm, 470 ps FWHM) was used for excitation of OH. The fluorescence from the laser sheet was imaged onto a fast gated intensified camera with a 400 ps gate width. The short laser pulse minimizes the collisional redistribution of population in the ground state during excitation, while the short camera gate avoids significant quenching of the excited-state fluorescence. The fluorescence signal obtained in this way is a direct measure of the population in a selected quantum state. In contrast to common nanosecond LIF signals no corrections on variations of the collisional environment are necessary. This collision-insensitive approach to two-dimensional LIF yields an OH detection limit of 10 ppm in a cube of 330 µm per side with a single 1 mJ laser pulse. A rate-equation model is used to estimate the effects on the observed signal of fluctuations in pulse energy and duration, laser-camera timing jitter, and spatial variations in the collisional environment.     

Excitation and relaxation of metastable state NaK(1 3pi) at high vibrational levels

The authors have investigated collision vibrational energy transfer rate constants in NaK[1 3pi(v)] and He system. Pump laser excitation of the spin-forbidden band was used to produce very highly vibrationally excited metastable state NaK[1 3pi (v = 22, 21, 20)]. The probe laser was used to excite the 1 3pi (v = 22, 21, 20) to 5 3pi(v'). Laser induced fluorescence (LIF) from 5 3pi --> 1 3sigma+ transition was used to follow the collision dynamics. The semilog plots of time-resolved LIF was obtained. The slopes yielded the effective lifetimes. From such data several Stern-Volmer plots could be constructed and the relaxation rate constants could be extracted for the sum of all processes that give rise to the decay of the prepared vibrational state. The rate constants (in units of 10(-11) cm3 x s(-1)) for v being 22, 21 and 20 are 1.4 +/- 0.1, 1.2 +/- 0.1 and 1.0 +/- 0.1, respectively. The vibrational relaxation rate is increasing with vibrational quantum number. In order to determine the importance of multiquantum relaxation, it is necessary to measure the relative population of both the prepared state and collisionally populated states. By the kinetic equations governing up to delta(v) = 2 transitions, the time dependence of populations of the vibrational states were obtained. With the help of the integrating the population equations over all time, the importance of the two-quantum relaxation could be studied experimentally. By varying the delay between the pump and the probe laser, the He pressure dependent vibrational state specific decay could be measured. The time evolutions and relative intensities of the three states v = 22, 21 and 20 by preparing v = 22 were obtained. Using experimental data the rate constants (in units of 10(-11) cm3 x s(-1)) for v = 22 --> 21 and v = 22 --> 20 are 0.67 +/- 0.15 and 0.49 +/- 0.12, respectively. The single quantum relaxation accounts for only about 48% of the total relaxation out of v = 22. Multi-quantum relaxation (delta(v) > 1) was found to be important at high vibrational states.     

便携式激光诱导荧光检测器的研制

采用共聚焦光学结构,并用激光二极管泵浦固体激光器作为激发光源,研制出一种小型荧光检测系统,该系统采用模块化结构,具有何种小,成本低,灵敏度高,易操作等优点,若适配检测池模块可满足不同的分离体系。     

激光场中锂原子发射的电离阈值以下低阶谐波的研究

利用单电子近似下锂原子精确的模型势,通过数值求解三维含时薛定谔方程的方法,研究了锂原子在激光场中发射低阶谐波的性质,研究结果表明,对于锂原子电离阈值以下的低阶谐波,除了通常的奇次谐波外,还有侧峰结构出现,运用同步压缩变换技术(SST)分析这些低阶谐波的辐射特性,我们发现这些侧峰是由原子在激光场中的缀饰态之间的跃迁和无场下激发态到基态的跃迁组成的,如果当激光脉冲结束后,仍有发射的侧峰,其位置与主峰之间的能量差可以用来估算原子激发态在激光场中的最大Stark移动.     

A novel double-pulse laser plasma spectroscopic technique for H analysis in metal samples utilizing transversely excited atmospheric-pressure CO2 laser-induced metastable He atoms

The analysis of hydrogen in a metal sample (zircaloy-4), which is usually difficult to perform using conventional laser-induced breakdown spectroscopy (LIBS) techniques, has been achieved using a double-pulse technique under He gas at atmospheric pressure. In this technique, a transversely excited atmospheric-pressure (TEA) CO₂ laser (1.5 J, 200 ns) was focused onto the metal surface to induce a strong He gas plasma whilst simultaneously focussing a Nd-doped yttrium aluminum garnet (Nd:YAG) laser (120 mJ, 8 ns), synchronized with the TEA CO2 laser, onto the metal to ablate atoms into the resulting He gas plasma. The emission spectrum obtained shows a narrow H linewidth with low background intensity and long lifetime emission, thereby indicating that excitation takes place via metastable He atoms. The H emission from H₂O can be suppressed by a careful pretreatment involving heating the sample in a vacuum chamber.     

Energy pooling to the level arising from collisions between pairs of metastable atoms

The energy-pooling rate coefficient for the process has been measured. The barium atoms were excited by a cw diode laser tuned to the frequency of the 791.3 nm intercombination line and the metastable atoms in the 6s5d state were produced due to radiative and collisional depopulation of the laser-excited 6s6p state. The measurements were performed at number densities of about and at 30 mbar argon as the buffer gas. Most of the barium ground state atoms in the excitation zone were transferred to the trip let metastable state at the laser pump power applied. The energy pooling rate coefficient was determined by comparing the fluorescence intensity of the barium 553.6 nm resonance line and the fluorescence intensity of the intercombination line 791.3 nm. In addition, the populations of the metastable atoms were probed with low intensity laser radiation from a single mode ring dye laser. The rate coefficient was found to be at . Received: 11 April 1997 / Revised: 24 September 1997 / Accepted: 10 December 1997     

稀土原子与离子的自然辐射寿命测量

概述了当前自由原子和离子的激发态自然辐射寿命测量技术的进展。以LaⅠ和PrⅡ为例,系统介绍了几种稀土元素自由原子和离子激发态寿命测量技术并分析了它们的优缺点;以SmⅡ为例,详细介绍了激光烧蚀产生自由原子(离子)技术及结合激光诱导荧光时间分辨光谱技术进行激发态寿命测量的优缺点。最后,探讨了改进上述技术局限性的解决思路,以期进一步提高辐射寿命测量的精确度。