Enhancement of near-band edge photoluminescence of ZnO thin films by employing MgF2 buffer layer

ZnO/MgF2/ZnO sandwich structure films were fabricated. The effects of a buffer layer on structure and optical properties of ZnO films were investigated by X-ray diffraction, photoluminescence, optical transmittance and absorption measurements. Measurement results showed that the buffer layer had the effects of improving the quality of ZnO films and releasing the residual stresses in the films. The near-band edge emissions of ZnO films deposited on the MgF2 buffer layer were significantly enhanced compared with those deposited on bare substrate due to the smaller lattice mismatch between MgF2 and ZnO than that between fused silica and ZnO. (c) 2006 Elsevier B.V. All rights reserved.

The study on the interface adhesion comparison of the MgF2, Al2O3, SiO2 and Ag thin films

Adhesion between the interface of pure silver thin film and three kinds of low refractive index coatings MgF2, Al2O3, SiO2 were compared in this article. The results indicated that the adhesion of Al2O3 and Ag was evidently superior to that of MgF2 and Ag, and the adhesion of MgF2 and Ag was evidently superior to that Of SiO2 and Ag. Reasons were analyzed accordingly. On the other hand, we compared the effect on the optical characteristic of Ag film when these three kinds of films were used as protective coatings and enhanced coatings. Considering the difference of the adhesion between Ag and MgF2, Al2O3, SiO2, suited uses are given for each other. © 2004 Elsevier B.V. All rights reserved.

Study of Al2O3/MgF2 HR coatings at 355 nm

With the present work we tried to study the effective methods to improve the laser-induced damage threshold (LIDT) and reflectance of HR coatings at 355 nm. The work presented in this paper wits part of an ongoing study about vacuum annealing. It was dedicated to study the effects Of Vacuum annealing with different temperature gradients on the structure, optical properties and laser-induced damage threshold (LIDT) of 355nm Al2O3/MgF2HR coatings. A number of samples were prepared by electron beam evaporation using the same deposition process with an optimal deposition temperature of 280 degrees C. After deposition, samples were annealed in the coating chamber for 3 h with different temperature gradients. Morphologies of the samples were observed by Leica-DMRXE. Microscope, Structure of the samples had been characterized by X-ray diffraction (XRD). Transmittance and reflectance of the samples were measured by Lambda 900 Spectrometer, The LIDT of the samples was measured by a 355 nm Nd:YAG laser with a pulse width of 8 ns. It was found that the temperature gradient of vacuum annealing had significant effects on the morphology, structure, absorption, and LIDT of the samples, (c) 2005 Elsevier Ltd. All rights reserved.

退火对电子束热蒸发193nm Al2O3/MgF2反射膜性能的影响

设计并镀制了193nm Al2O3/MgF2反射膜,对它们在空气中分别进行了250-400℃的高温退火,测量了样品的透射率光谱曲线和绝对反射率光谱曲线.发现样品在高反射区的总的光学损耗随退火温度的升高而下降,而后趋于饱和.采用总积分散射的方法对样品在不同退火温度下的散射损耗进行了分析,发现随着退火温度的升高散射损耗有所增加.因此,总的光学损耗的下降是由于吸收损耗而不是散射损耗起主导作用.对Al2O3材料的单层膜进行了同等条件的退火处理,由它们光学性能的变化推导出它们的折射率和消光系数的变化,从而解释了相应

High-reflectance 193 nm Al2O3/MgF2 mirrors

Thin-film single layers of Al2O3 and MgF2 were deposited upon super polished fused-silica by electron-beam evaporation. The subsequent optical constants n and k were reported for the spectral range of 180-230 nm. High-reflectance dense multilayer coatings for 193 nm were designed on the basis of the evaluated optical constants and produced. The spectra of the reflectance of HR coatings were compared to the theoretical calculations. HR mirrors of 27 layers with a reflectance of more than 98% were reported. (c) 2004 Elsevier B.V. All rights reserved.

高反射率193nm Al2O3／MgF2反射膜的实验研究

用电子束热蒸发方法在熔融石英基底上沉积了Al2O3和MgF2两种材料的单层膜，研究了两种材料的光学特性，采用光度法计算并给出了薄膜材料在180～230nm的折射率n／和消光系数k的色散曲线。以两种材料作为高低折射率材料组合，采用1／4波长规整膜系设计并镀制了193nm的高反射膜，反射膜在退火后的反射率在193nm达到96％以上。结果表明在一定工艺条件下Al2O3和MgF2两种材料能够在193nm获得较好的光学性能，适用于高反射膜的制备。

Influence of substrate temperature on properties of MgF2 coatings

Thermal boat evaporation was employed to prepare MgF2 single-layer coatings upon both JGS1 and UBK7 substrates at different substrate temperatures. Microstructure, transmittance and residual stress of these coatings were measured by X-ray diffraction, spectrophotometer, and optical interferometer, respectively. Measurement of laser induced damage threshold (LIDT) of the samples was performed at 355 nm, 8 ns pulses. The results showed that high substrate temperature was beneficial to crystallization of the film. Above 244 degrees C, the refractive index increased gradually with the substrate temperature rising. Whereas, it was exceptional at 210 degrees C that the refractive index was higher than those deposited at 244 and 277 degrees C. The tensile residual stresses were exhibited in all MgF2 films, but not well correlated with the substrate temperature. In addition, the stresses were comparatively smaller upon JGS1 substrates. A tendency could be seen that the LIDTs reached the highest values at about 244 degrees C, and the films upon JGS1 had higher LIDTs than those upon UBK7 substrates at the same temperature. Meanwhile, the damage morphologies showed that the laser damage of the coating resulted from an absorbing center at the film-substrate interface. The features of the damages were displayed by an absorbing center dominated model. Furthermore, the reason of the difference in LIDT values was discussed in detail. (C) 2007 Elsevier B.V. All rights reserved.

沉积温度对热舟蒸发MgF2薄膜性能的影响

采用热舟蒸发方法沉积了氟化镁（MgF2）材料的单层膜，沉积温度从200℃上升到350℃，间隔为50℃。测量了样品的透射率和反射率光谱曲线，进行了表面粗糙度的标定，并在此基础上进行了光学损耗及散射损耗的计算。同时对355nm波长处的激光诱导损伤阈值进行了测量。结果表明：随着沉积温度的升高，光学损耗增加;在短波长范围散射损耗在光学损耗中所占比例很小，光学损耗的增加主要由吸收损耗引起；在355nm波长处的损伤阈值变化与吸收损耗的变化趋势相关，损伤机制主要是吸收起主导作用。样品的微缺陷密度也是影响损伤阈值的一个重要因素，损伤阈值随缺陷密度的增加而降低。

THE VALENCY AND SPECTRA OF SAMARIUM IONS IN MF(2)-MGF2 (M=CA, SR, BA)

The phosphors MMgF(4)(M = Ca, Sr, Ba) doped with samarium ions are synthesized in different atmospheres using solid phase reaction at high temperature. Samarium has been first stabilized in the divalent state in SrMgF4 and BaMgF4 matrices. Effects of matrices on the valent state of samarium ions are briefly discussed.

四氧化二氮对卫星漫射试片氟化镁涂层的污染和侵蚀

利用漫反射率、X射线光电能谱和质谱等测量方法,研究了固态和气态四氧化二氮(N2O4)对漫反射试片氟化镁(MgF2)涂层表面的污染情况.实验表明,固态N2O4对MgF2涂层有严重侵蚀作用,N2O4固粒污染后的涂层表面漫反射率下降了20%～30%.在一定的时间内,气态N2O4对涂层表面的影响显著地依赖它的压力.试片在压力为6.9×104 Pa和200Pa的N2O4蒸气中分别放置10 min,前者厚度为40μm的MgF2涂层基本消失,表面漫反射率下降约20%;后者涂层表面的原子组成和漫反射率变化很小.还给出了MgF2涂层表面N2O4分子吸附摩尔密度,以及与涂层表面碰撞的N2O4分子通过化学吸附过程提取MgF2的几率.

四氧化二氮对卫星漫反射试片氟化镁涂层的污染和侵蚀

利用漫反射率、X射线光电能谱和质谱等测量方法,研究了固态和气态四氧化二氮(N2O4)对漫反射试片氟化镁(MgF2)涂层表面的污染情况.实验表明,固态N2O4对MgF2涂层有严重侵蚀作用,N2O4固粒污染后的涂层表面漫反射率下降了20%～30%.在一定的时间内,气态N2O4对涂层表面的影响显著地依赖它的压力.试片在压力为6.9×104 Pa和200Pa的N2O4蒸气中分别放置10 min,前者厚度为40μm的MgF2涂层基本消失,表面漫反射率下降约20%;后者涂层表面的原子组成和漫反射率变化很小.还给出了MgF2涂层表面N2O4分子吸附摩尔密度,以及与涂层表面碰撞的N2O4分子通过化学吸附过程提取MgF2的几率.

Bi-doped BaF2 crystal for broadband near-infrared light source

Bi-doped BaF2 crystal was grown by the temperature gradient technique and its spectral properties were investigated. The absorption, emission and excitation spectra were measured at room temperature. Two broadband emissions centered at 1070 and 1500 nm were observed in Bi-doped BaF2 crystal. This extraordinary luminescence should be ascribed to Bi-related centers at distinct sites. We suggest Bi2+ or Bi+ centers adjacent to F vacancy defects are the origins of the observed NIR emissions. (C) 2009 Optical Society of America

The ultrafast excitation processes in femtosecond laser-induced damage in dielectric omnidirectional reflectors

A pump and probe system is developed, where the probe pulse duration tau is less than 60 fs while the pump pulse is stretched up to 150-670 fs. The time-resolved excitation processes and damage mechanisms in the omnidirectional reflectors SiO2/TiO2 and ZnS/MgF2 are studied. It is found that as the pump pulse energy is higher than the threshold value, the reflectivity of the probe pulse decreases rapidly during the former half, rather than around the peak of the pump pulse. A coupled dynamic model based on the avalanche ionization (AI) theory is used to study the excitation processes in the sample and its inverse influences on the pump pulse. The results indicate that as pulse duration is longer than 150 fs, photoionization (PI) and AI both play important roles in the generation of conduction band electrons (CBEs); the CBE density generated via AI is higher than that via PI by a factor of 10(2)-10(4). The theory explains well the experimental results about the ultrafast excitation processes and the threshold fluences. (c) 2006 American Institute of Physics.