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.     

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.     

Optically pumped infrared stimulated radiation in Pr~(3+):Y_2SiO_5

The infrared stimulated radiation of 1D2-3F2 and 1D2-3H6 transitions in Pr3+:Y2SiO5 (YSO) via pulsed laser pumping has been observed. The threshold energy, temperature dependence and divergence angle for the stimulated radiation are also measured.     

新型吡咯甲川-BF2化合物的光谱和激光性能研究

合成了6个最大吸收波长位于517nm-524nm的新型吡咯甲川－BF2化合物,测量了它们在无水乙醇溶液中的电子吸收光谱,测试结果表明,6个化合物的激光性能全部优于若丹明6G。     

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).     

E-3-二茂铁基-2-丙烯醛的简便合成方法

由二茂铁甲醛和Nagata试剂通过Wittig-Horner反应生成反式二茂铁丙烯醛. 该方法以易得的原料、温和的反应条件和高收率制备了目标产物.     

Compressing ultrafast electron pulse by radio frequency cavity

An ultrafast electron diffraction technique with both high temporal and spatial resolution has been shown to be a powerful tool to observe the material transient structural change on an atomic scale.The space charge forces in a multi-electron bunch will greatly broaden the electron pulse width,and therefore limit the temporal resolution of the high brightness electron pulse.Here in this work,we design an ultrafast electron diffraction system,and utilize a radio frequency cavity to realize the ultrafast electron pulse compression.We experimentally demonstrate that the stretched electron pulse width of14.98 ps with an electron energy of 40 keV and the electron number of 1.0 ×10~5 can be maximally compressed to about0.61 ps for single-pulse measurement and 2.48 ps for multi-pulse measurement by using a 3.2-GHz radiofrequency cavity.We also theoretically and experimentally analyze the parameters influencing the electron pulse compression efficiency for single-and multi-pulse measurements by considering radiofrequency field time jitter,electron pulse time jitter and their relative time jitter.We suggest that increasing the electron energy or shortening the distance between the compression cavity and the streak cavity can further improve the electron pulse compression efficiency.These experimental and theoretical results are very helpful for designing the ultrafast electron diffraction experiment equipment and compressing the ultrafast electron pulse width in a future study.     

The photoluminescence of ZnSe bulk single crystals excited by femtosecond pulse

This paper reports on the photoluminescence spectra of ZnSe single crystal with trace chlorine excited by the femtosecond laser pulse. Three emission bands, including second-harmonic-generation, two-photon-excited peak and a broad band at 500--700nm, were detected. The thermal strain induced by femtosecond pulse strongly influences the photoluminescence of ZnSe crystal. The corresponding strain \va in ZnSe crystal is estimated to be about 8.8 \ti10^-3 at room temperature. The zinc-vacancy, as the main point defect induced by femtosecond pulse, is successfully used to interpret the broad emission at 500--700nm. The research shows that self-activated luminescence possesses the recombination mechanism of donor--vacancy pair, and it is also influenced by a few selenium defects and the temperature. The rapid decrease in photoluminescence intensity of two-photon-excited fluorescence and second-harmonic generation emission at lower temperature is attributed to the fact that more point defects result in the thermal activation of the two-photo-absorption energy converting to the stronger recombination emission of chlorine--zinc vacancy in 500--700nm. The experimental results indicate that the femtosecond exciting photoluminescence shows a completely different emission mechanism to that of He--Cd exciting luminescence in ZnSe single crystal. The femtosecond laser exhibits a higher sensitive to the impurity in crystal materials, which can be recommended as an efficient way to estimate the trace impurity in high quality crystals.     

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.     

稠环芳烃有机物的三阶非线性光学性能研究

采用Ｎｄ：ＹＡＧ皮秒锁模脉冲激光λ＝５３２．０ｎｍ,运用３Ｄ前向简并四波混频（ＤＦＷＭ）的方法,测量了稠环芳烃中的１．２．５．６二苯并蒽（Ｃ２２Ｈ１４）,１．２．８．９．二苯并五苯（Ｃ３０Ｈ１８）的三阶非线性极化率Ｘ＾（３）,非线性折射系数ｎ２以及三阶非线性的时间响应。发现该类材料具有较大的非线性效应,文中分析了非线性形成机制以及相关的影响因素。