The dependence of high-order harmonic generation on the laser frequency and inter-nuclear distance from multi-atom molecular ions

High-order harmonic generation from one-dimensional (1D) multi-atom molecular ions in an ultra-short laser field is theoretically investigated. The dynamics of the electron in a linearly polarized intense laser field is analyzed in terms of 1D Schrodinger equation with the Crank-Nicolson algorithm. The dependence of high-order harmonics on the laser frequency and the inter-nuclear distance is discussed. It is found that the optimum range of inter-nuclear distance should be changed to get extended harmonic generation for different laser frequency, and the lower frequency laser pulse is favorable to higher order harmonic generation as the inter-nuclear distance increases.     

Spectroscopic and lasing characteristics of 1,3,5,7-tetramethyl-8-ethyl-pyrromethene-BF2 complex

The basic optical properties of the newly synthesized pyrromethene-BF2 derivative (Compound 1) were investigated systematically by its ultraviolet to visible (UV-visible) absorption, fluorescence and triplettriplet absorption. Its lasing characteristics were measured on a dye laser system pumped by a continuous wave Ar ion laser. The results suggest that, compared with the typical pyrromethene-BF2 dye such as P546, Compound 1 possesses stronger fluorescence and lower triplet-triplet absorption over its fluorescence spectral region. Excellent laser properties were also observed for Compound 1. It outperforms the commercially available benchmark laser dye rhodamine 6G in laser wavelength tuning range, which proves that Compound 1 is probably a potential candidate to be developed as the all-solid-state laser material.     

中间能级失谐量对Y型四能级自发辐射量子干涉的影响

文章运用密度矩阵方程，在Y型四能级系统中计算和讨论了中间共振增强能级的失谐对自发辐射量子干涉效应的影响。结果表明，两步激发而非双光子激发是产生自发辐射干涉效应的主要激发机制；失谐量过大，则因两步激发的失效而导致有关量子干涉效应的消失。以上分析对正确选取产生量子干涉效应的能级系统及理解有关过程是很有意义的。     

Study on the interaction of anticancer drug mitoxantrone with DNA by fluorescence and Raman spectroscopies

Mitoxantrone, a clinically useful antitumour antibiotic for leukaemia and breast cancer, has received more attentions. In this paper, the interaction between mitoxantrone and calf thymus DNA is investigated by Raman and fluorescence spectroscopies, and the binding site of mitoxantrone to calf thymus DNA is explored. The results showed that mitoxantrone interacts with calf thymus DNA bases by the intercalation of anthracycline into the base pair plane of adenine (A) and thymine (T), and it results in the disruption of the hydrogen bonds between calf thymus DNA bases, and thus the calf thymus DNA double-strand can be disrupted into the B-form DNA double-strand segments.     

Laser induced crystallization of as-deposited amorphous Ge_2Sb_2Te_5 films

Crystallization is induced by pulsed laser irradiation of as-deposited amorphous Ge_2Sb_2Te_5 films. Changes of the irradiated areas have been analyzed with the reflectivity contrast. As laser fluences increasing, the reflectivity contrast increases from 0%-2% to 14%-16%, which indicates the structure of asdeposited films transforms from amorphous to crystalline phases. The process of crystallization driven by the movement and rearrangement of atoms is described. And also the influence of the pulse duration on the threshold of crystallization is discussed, the results show that a lower threshold of crystallization can be produced for as-deposited films irradiated by the laser with short pulse duration. However, by the laser with long pulse duration, crystallization can only be formed with a higher threshold. The crystallization of films by irradiation of laser pulses is studied by Raman spectra.     

Nonlinear optical properties of Er_2O_3-doped 75Nb_2O_5-20TeO_2-5ZnO glasses

We have performed time-resolved degenerate four-wave mixing (DFWM) experiments in 75Nb2O5-20TeO2-5ZnO glasses doped by Er2O3 at different excitation intensities and lattice temperatures. DFWM signal exhibits three peaks at high excitation intensities, where a main peak appears at zero time delay and two rather weak side peaks locate symmetrically at the negative and positive time delay, respectively. The main peak is attributed to local-field effect and two side peaks are attributed to Coulomb interaction (CI).     

掺杂CeO2的75TeO2-25Nb2O5-5ZnO飞秒激光诱导瞬态光栅的研究

用泵浦探测技术研究了掺杂CeO₂的75TeO₂-25Nb₂O₅-5ZnO玻璃在飞秒激光诱导的瞬态光栅多级自衍射。从拉曼和吸收光谱中研究了玻璃的结构特性，并证明了此玻璃中存在Ce3+离子。这种瞬态光栅起因于光克尔效应，并通过Ce3+离子中1S0?1F3电子能级跃迁形成的激发态粒子数光栅而改善，一级衍射信号的转换效率可达到11%。这些实验结果显示了掺杂CeO₂的75TeO₂-25Nb₂O₅-5ZnO飞玻璃在全转换开关中具有广泛应用。     

Na2中由一对耦合能级相干叠加导致的双光子吸收的干涉增强效应

在中间共振增强能级是一对波函数叠加的耦合能级的钠分子菱形四能级系统中，实验观察了由该两耦合能级的相干叠加作用所导致的不等频双光子吸收的干涉增强效应，并运用密度矩阵方程对这一实验现象进行了计算，其结果与实验符合得很好. 关键词： 干涉增强 双光子吸收 菱形四能级系统 耦合能级     

基于碰撞产生的频域和时域内的量子干涉效应研究

从理论和实验两方面对以往较少涉及的原子-分子混合体系中基于碰撞而产生间距较大多能级间的相干和两延时波包间的相干及量子干涉效应进行研究,揭示通过碰撞这种非相干过程可产生在频域内具有较大能级间距多能级间的相干和时域内两延时波包间的相干.运用半经典密度矩阵理论及缀释态理论对碰撞产生的多能级系统量子干涉效应进行计算和分析;同时实验上用ns脉冲染料激光器观察到钠原子-分子混合体系中基于等频双光子两步激发及钠原子-分子混合激发而产生的钠原子3S-3P(1/2,3/2)-5S(或4D)系统基于碰撞产生的频域和时域内的量子干涉效应.本工作为进一步运用非相干碰撞过程研究较大间距多能级间和两延时波包间的相干提供了一种新的有效的方法,可望在高灵敏高精度激光光谱、原子分子激发态结构信息及物理化学过程的控制等方面具有广泛的应用.     

基于碰撞感应激发而产生相干相长的研究

运用半经典密度矩阵方法研究了一个开放四能级系统中基于碰撞感应激发而产生的干涉相长.在该四能级系统中,一个公共上能级与两个间距较大的下能级所组成Λ型三能级量子拍结构由一个相干激光场耦合,同时该公共上能级通过真空模与另一下能级耦合.