Fluorescence properties in a single driven four-level atomic system

The spontaneous emission decay dynamics of a tripod configuration four-level atom driven by a single laser field is studied.Under different initial conditions,we discuss the effects of quantum interference and detuning of external driving field on atomic spontaneous emission properties.For the larger detuning,the interesting phenomena of the spectral line narrowing are found which stem from the contribution of external driving field.     

Coherence generation and population transfer in a three-level ladder system

This work explores the effect of spontaneous emission on coherence generation and population transfer in a threelevel ladder atomic system driven by two pulses in counterintuitive order.With adiabatic evolution and the weakdephasing approximation,we find that a large coherence and population transfer can be achieved even with spontaneous decay rate.The maximum coherence and population transfer decrease with the increase of spontaneous decay rate from the highest state to intermediate state.But this effect can be compensated by shortening the pulse width and enlarging the delay time.Results show that the coherence generation and population transfer never depend on the spontaneous decay rate from the intermediate state to ground state.The validity of the analytic solution is examined by numerical calculation.     

用共振增强多光子电离方法研究几种含溴化合物的光解

利用飞行时间质谱仪(TOF)和共振增强多光子电离(REMPI)方法, 研究了两种正一溴代烷烃(C₂H₅Br, n-C₃H₇Br)和溴苯(C₆H₅Br)在234及267 nm附近的光解. 测出了这几种含溴化合物在不同波长下光解产物Br^*和Br的分支比N(Br*)/N(Br), 并根据从头计算结果, 解释了这几种含溴化合物光解产物的分支比随光解波长变化的趋势及几个低激发态势能面之间的关系.     

Quantum interference effects on the probe amplification without and with inversion in a four-level system

A four-level system driven by two coherent fields is considered. It is shown that in the presence of an incoherent pump, the probe gain at a short wavelength can be achieved due to the quantum interference. Our density matrix calculation provides the conditions for probe amplification from different origins, including gain without population inversion on any state basis, gain with population inversion on the dressed-state basis, and gain with population inversion on the bare-state basis. Also, by controlling the Rabi frequency of the coupling field a total change from non-inversion to inversion can be achieved which does not depend on the intensity of the incoherent pump.     

(2+2)RESONANCE-ENHANCED MULTIPHOTON IONIZATION-FRAGMENTATION STUDY OF DIMETHYLAMINE

The multiphoton ionization spectra of dimethylamine are given in the 445-470 nm region. A time of flight mass spectrometer was used,and experiment was done under collision free condition. It is found that (2+2) resonance enhanced multiphoton ionization through (n_N,3s) Rydberg state produces parent ions which endure pseudo-α and C—N bond cleavages. The former forms CH₃N⁺H=CH₂ ions,and the latter gives CH₂=N⁺H₂ ions .     

液相色谱故障排除──依据物理性质选择溶剂

讨论如何依据溶剂的粘度、沸点、混溶性、洗脱强度和极性选择液相色谱用溶剂。     

液相色谱中的故障排除——溶剂的寿命和降解

讨论了作为液相色谱流动相组分的醚、酮、氯代烷、烷烃、水等溶剂的降解及其导致的色谱困难,并提出了解决方法。     

Hf微量掺杂Sm2Ce2O7固溶体制备及热物理性能

采用高温固相烧结法制备了Sm2(Ge1-xHfx)2O7(x=0,0.025,0.05,0.075,0.1)固溶体,并对其相组成、显微组织及热物理性能进行了分析.结果表明,所合成的固溶体具有单一的萤石结构,其相对致密度均在90;以上.Hf掺杂增强了声子的散射程度,从而使其热导率与Sm2Ce2O7相比明显降低.Hf较小的离子半径使得其热膨胀系数随HfO2掺杂量增加而降低,但仍然满足热障涂层的要求.     

氯苯分子第一激发态超快动力学

利用时间分辨飞秒光电子影像技术结合时间分辨质谱技术, 研究了氯苯分子第一激发态的超快过程. 266.7 nm单光子将氯苯分子激发至第一激发态. 母体离子时间变化曲线包括了不同的双指数曲线. 一个是时间常数为(152±3) fs的快速组分, 另一个是时间常数为(749±21) ps的慢速组分. 通过时间分辨的光电子影像得到了时间分辨的光电子动能分布和角度分布. 时间常数为(152±3) fs的快速组分反映了第一激发态内部的能量转移过程, 这个过程归属为氯苯分子第一激发态耗散型振动驰豫过程. 时间常数为(749±21) ps的慢速组分反映了第一激发态的慢速内转换过程. 另外, 实验实时观察到典型的非对称陀螺分子(氯苯)激发态的非绝热准直和转动退相干现象. 并推算出第一次转动恢复时间为205.8 ps (C类型)和359.3 ps (J类型).     

激光质谱法对痕量污染物的快速检测

有机污染正越来越引起人们的注意,然而现有的对包括具有致癌作用的最大的一类化学物质芳香烃在内的许多有机物的分析方法需要对含有污染物的气体进行预先处理.其主要缺点是复杂耗时,不能做到理想的实时在线分析.激光质谱法通过共振增强多光子电离(REMPI)把紫外光谱和飞行时间质谱(TOF-MS)结合起来,具有高灵敏度、高选择性和分析速度快的特点.在介绍了激光质谱法的原理后,介绍了一小型化的可移动激光质谱装置,其中使用一台小型KrF准分子激光器(248 nm),可以对芳香烃进行多组分检测.该装置对机动车尾气的实时测量结果表明激光质谱法用于污染分析时具有其他分析手段很少能同时具备的一些显著优点：多组分探测,在机动车尾气中同时测量到苯、甲苯、二甲苯、三甲苯、萘和甲基萘等多种芳香烃污染物;灵敏度高(0.1mg/m³);测量速度快(0.1 s);对样品不经处理,进行直接分析.