A picosecond widely tunable deep-ultraviolet laser for angle-resolved photoemission spectroscopy

We develop a picosecond widely tunable laser in a deep-ultraviolet region from 175 nm to 210 nm,generated by two stages of frequency doubling of a 80-MHz mode-locked picosecond Ti:sapphire laser.A β-BaB2O4 walk-off compensation configuration and a KBe2BO3F2 prism-coupled device are adopted for the generation of second harmonic and fourth harmonics,respectively.The highest power is 3.72 mW at 193 nm,and the fluctuation at 2.85 mW in 130 min is less than ±2%.     

Disappearance of Superconductivity and a Concomitant Lifshitz Transition in Heavily Overdoped Bi_2Sr_2CuO_6 Superconductor Revealed by Angle-Resolved Photoemission Spectroscopy

By partially doping Pb to effectively suppress the superstructure in single-layered cuprate Bi_2Sr_2CuO_(6+δ)(Pb-Bi2201) and annealing them in vacuum or in high pressure oxygen atmosphere, a series of high quality Pb-Bi2201 single crystals are obtained with T_c covering from 17 K to non-superconducting in the overdoped region. High resolution angle resolved photoemission spectroscopy measurements are carried out on these samples to investigate the evolution of the Fermi surface topology with doping in the normal state. Clear and complete Fermi surfaces are observed and quantitatively analyzed in all of these overdoped Pb-Bi2201 samples. A Lifshitz transition from holelike Fermi surface to electron-like Fermi surface with increasing doping is observed at a doping level of ~0.35. This transition coincides with the change that the sample undergoes superconducting-to-non-superconducting states.Our results reveal the emergence of an electron-like Fermi surface and the existence of a Lifshitz transition in heavily overdoped Bi2201 samples. This provides important information in understanding the connection between the disappearance of superconductivity and the Lifshitz transition in the overdoped region.     

Common Features in Electronic Structure of the Oxypnictide Superconductors from Photoemission Spectroscopy

High resolution photoemission measurements are carried out on non-superconducting LaFeAsO parent com- pound and various superconducting RFeAs（O1-ZFx） （R=La, Ce and Pr） compounds. It is found that the parent LaFeAsO compound shows a metallic character. By extensive measurements, several common features are identified in the electronic structure of these Fe-based compounds： （1） 0.2 eV feature in the valence band, （2） a universal 13-16 meV feature, （3） near EF spectral weight suppression with decreasing temperature. These uni- versal features can provide important information about band structure, superconducting gap and pseudogap in these Fe-based materials.     

Detailed electronic structure of three-dimensional Fermi surface and its sensitivity to charge density wave transition in ZrTe_3 revealed by high resolution laser-based angle-resolved photoemission spectroscopy

The detailed information of the electronic structure is the key to understanding the nature of charge density wave(CDW) order and its relationship with superconducting order in the microscopic level. In this paper, we present a high resolution laser-based angle-resolved photoemission spectroscopy(ARPES) study on the three-dimensional(3 D) hole-like Fermi surface around the Brillouin zone center in a prototypical quasi-one-dimensional CDW and superconducting system ZrTe_3. Double Fermi surface sheets are clearly resolved for the 3 D hole-like Fermi surface around the zone center. The3 D Fermi surface shows a pronounced shrinking with increasing temperature. In particular, the quasiparticle scattering rate along the 3 D Fermi surface experiences an anomaly near the charge density wave transition temperature of ZrTe_3(～ 63 K). The signature of electron–phonon coupling is observed with a dispersion kink at ～ 20 me V; the strength of the electron–phonon coupling around the 3 D Fermi surface is rather weak. These results indicate that the 3 D Fermi surface is also closely connected to the charge-density-wave transition and suggest a more global impact on the entire electronic structure induced by the CDW phase transition in ZrTe_3.     

位错对BBO晶体光学均匀性的影响

本文报道了BBO晶体中位错密度对光学均匀性的影响.样品的光学均匀性是利用Wyko RTI 4100型干涉仪进行测量.采用侵蚀法观测BBO晶体{001}面的位错密度,在一定的侵蚀条件下,观察到BBO晶体{001}面上的位错露头为突起的正三方锥形,底边与X轴平行.在显微镜下测量出样品的蚀坑密度.实验证明,随着位错密度的增加BBO晶体的光学均匀性逐渐变差.     

紫外与深紫外非线性光学晶体的新进展

随着光刻、激光微加工以及激光光谱仪的发展,紫外与深紫外光谱区的相干光源变得越来越重要.本文简要地回顾了使用阴离子基团理论发展新型硼酸盐系列紫外与深紫外非线性光学晶体的历史,同时系统地介绍了这些硼酸盐系列晶体的线性和非线性光学性质.最后给出一些产生紫外与深紫外谐波输出的典型例子以及它们的应用.     

LBO晶体超光滑表面抛光机理

胶体SiO2抛光LBO晶体获得无损伤的超光滑表面,结合前人对抛光机理的认识,探讨了超光滑表面抛光的材料去除机理,分析了化学机械抛光中的原子级材料去除机理.在此基础上,对胶体SiO2抛光LBO晶体表面材料去除机理和超光滑表面的形成进行了详细的描述,研究抛光液的pH值与材料去除率和表面粗糙度的关系.LBO晶体超光滑表面抛光的材料去除机理是抛光液与晶体表面的活泼原子层发生化学反应形成过渡的软质层,软质层在磨料和抛光盘的作用下很容易被无损伤的去除.酸性条件下,随抛光液pH值的减小抛光材料的去除率增大;抛光液pH值为4时,获得最好的表面粗糙度.     

非线性光学晶体BaBPO5的生长、结构研究

本文采用顶部籽晶高温溶液法,以Li4P2O7为助熔剂,生长了大尺寸BaBPO5单晶.进行了BaBPO5晶体的结构测定,结果表明该晶体属三方晶系,空间群:P3221,晶胞参数为a=b=0.71329(10)nm,c=0.70368(14)nm,α=β=90°,γ=120°, Z=3.该晶体结构中沿[001]方向存在BO4四面体链,每一个硼氧四面体用它的两个顶点分别与两个PO4四面体相连组成螺旋状的链.硼氧四面体、磷氧四面体和钡氧多面体结合在一起形成一个三维网络结构.同时,对BaBPO5的粉末倍频效应进行了研究.     

K2Al2B2O7-NaF体系的热分析研究

用热分析的方法研究了KABO-NaF体系的物相关系,提出了KABO-NaF体系的赝二元相图.KABO和NaF可以形成低共熔体系,D KABO含量约30;时低共熔温度约为790℃.KABO在体系中的摩尔百分含量为30;～40;之间为KABO结晶区.KABO-NaF体系在500℃左右发生一个放热过程,675℃左右有一个复杂的吸热相变过程.     

氟硼铍酸钾晶体的生长、表面形貌和缺陷

采用自发成核方法,以KF-B2O3为助溶剂,在KBBF∶KF∶B2O3为1.5∶5.0∶0.8的体系中,较为重复地生长了尺寸较大的KBBF晶体,从中可加工出10mm×10mm×1.5mm的样品供测试和非线性谐波输出应用.晶体的理想外形由{0001}、{1010}、和{1011}三组单形构成.其宏观缺陷主要为连生、孪生、包裹体,宏观生长台阶和条纹、开裂等.并观察了晶体的表面形貌.