Self-stabilized passive, harmonically mode-locked stretched-pulse erbium fiber ring laser

We have studied a passive, harmonically mode-locked stretched-pulse erbium fiber ring laser with net positive dispersion that is self-stabilized by gain depletion and electrostriction. Periodic pulses with supermode suppression of >75 dB and picosecond jitter are achieved. The pulses are compressible to 125 fs by external chirp compensation. The repetition rate is 220 MHz, and the average power is as high as 80 mW.     

Defect structure and optical damage resistance of Hf:Fe:LiNbO3 crystals

A series of Hf:Fe:LiNbO₃ crystals were grown by the Czochralski technique with various doping concentrations of HfO₂. Their defect structures were analyzed by the UV-visible absorption spectra and infrared absorption spectra. The optical damage resistance of Hf:Fe:LiNbO₃ crystals was measured by the photo-induced birefringence change and the transmitted light spot distortion method. The results show that the optical damage resistance ability of Hf:Fe:LiNbO₃ crystals enhances remarkably with the HfO₂ concentration increasing when the HfO₂ concentration is lower than its threshold concentration (4 mol%). However, when the HfO₂ concentration exceeds its threshold concentration, the optical damage resistance ability of the crystals returns to decrease. This unusual behavior is explained by using the photovoltaic field produced in the crystals.     

Phase-incoherent superconducting pairs in the normal state of Ba(Fe(1-x)Co(x))₂As₂

The normal state properties of the recently discovered ferropnictide superconductors might hold the key to understanding their exotic superconductivity. Using point-contact spectroscopy we show that Andreev reflection between an epitaxial thin film of Ba(Fe(0.92)Co(0.08))?As? and a silver tip can be seen in the normal state of the film up to temperature T～1.3T(c), where T(c) is the critical temperature of the superconductor. Andreev reflection far above T(c) can be understood only when superconducting pairs arising from strong fluctuation of the phase of the complex superconducting order parameter exist in the normal state. Our results provide spectroscopic evidence of phase-incoherent superconducting pairs in the normal state of the ferropnictide superconductors.     

Subwavelength-resolution direct writing using submicron-diameter fibers

<正>A novel direct writing technique using submicron-diameter fibers is presented.This technique adopts contact mode in the process of writing,and submicron lines with different widths have been obtained. Experimental results demonstrate that the resolution of this technique can be smaller than the exposure wavelength of 442 nm,and 380-nm-wide line is achieved.In addition,the distribution of light fields in the photoresist layer is analyzed by finite-difference time-domain method.     

XANES speciation of mercury in three mining districts – Almadén,Asturias (Spain), Idria (Slovenia)

The mobility, bioavailability and toxicity of mercury in the environment strongly depend on the chemical species in which it is present in soil, sediments, water or air. In mining districts, differences in mobility and bioavailability of mercury mainly arise from the different type of mineralization and ore processing. In this work, synchrotron‐based X‐ray absorption near‐edge spectroscopy (XANES) has been taken advantage of to study the speciation of mercury in geological samples from three of the largest European mercury mining districts: Almadén (Spain), Idria (Slovenia) and Asturias (Spain). XANES has been complemented with a single extraction protocol for the determination of Hg mobility. Ore, calcines, dump material, soil, sediment and suspended particles from the three sites have been considered in the study. In the three sites, rather insoluble sulfide compounds (cinnabar and metacinnabar) were found to predominate. Minor amounts of more soluble mercury compounds (chlorides and sulfates) were also identified in some samples. Single extraction procedures have put forward a strong dependence of the mobility with the concentration of chlorides and sulfates. Differences in efficiency of roasting furnaces from the three sites have been found.     

Structural and electronic properties of group III Rich In0.53Ga0.47As(001)

The structural and electronic properties of group III rich In_0.53Ga_0.47As(001) have been studied using scanning tunneling microscopy/spectroscopy (STM/STS). At room temperature (300 K), STM images show that the In_0.53Ga_0.47As(001)–(4 × 2) reconstruction is comprised of undimerized In/Ga atoms in the top layer. Quantitative comparison of the In_0.53Ga_0.47As(001)–(4 × 2) and InAs(001)–(4 × 2) shows the reconstructions are almost identical, but In_0.53Ga_0.47As(001)–(4 × 2) has at least a 4× higher surface defect density even on the best samples. At low temperature (77 K), STM images show that the most probable In_0.53Ga_0.47As(001) reconstruction is comprised of one In/Ga dimer and two undimerized In/Ga atoms in the top layer in a double (4 × 2) unit cell. Density functional theory (DFT) simulations at elevated temperature are consistent with the experimentally observed 300 K structure being a thermal superposition of three structures. DFT molecular dynamics (MD) show the row dimer formation and breaking is facilitated by the very large motions of tricoodinated row edge As atoms and z motion of In/Ga row atoms induced changes in As–In/Ga–As bond angles at elevated temperature. STS results show there is a surface dipole or the pinning states near the valence band (VB) for 300 K In_0.53Ga_0.47As(001)–(4 × 2) surface consistent with DFT calculations. DFT calculations of the band-decomposed charge density indicate that the strained unbuckled trough dimers being responsible for the surface pinning.     

温度对潜望式激光通信终端SiC反射镜性能影响

分析了温度梯度和均匀温度对潜望式激光通信终端反射镜形变的影响,利用椭圆域上的Zernike多项式对椭圆反射镜的波前进行拟合,计算由于热形变导致的波前畸变误差,给出了星间激光通信终端反射镜均方根值、发射光束瞄准误差、接收端光强随温度梯度和均匀温度的变化关系。结果表明:温度梯度对反射镜的影响只是引起峰值光强的漂移和少许下降,当温度梯度为14 ℃/m时瞄准误差达2.1 μrad。均匀温度会引起接收端的光强分布变化,从而导致很大的瞄准误差和光强衰减,当均匀温度与参考温度的差值小于0.6 ℃时,由波前畸变误差引起的瞄准误差小于1 μrad,当差值大于0.6 ℃时,瞄准误差突然增大到几μrad,接收端光强分布发生变化,此时反射镜热形变引起的像散项对光强分布起重要作用。     

极紫外光刻系统物镜光学元件的支撑与分析

介绍了极紫外光刻系统物镜光学元件的支撑原理和支撑要求,分析了符合运动学支撑要求的物镜支撑结构和面形检测用支撑结构;针对支撑结构性能和支撑方案中关键问题进行了深入研究,并提出了相应的解决方案。最后建立了支撑结构的有限元模型,并在此基础上进行了重力场中的镜体变形分析和温度场作用下系统的热变形分析。分析结果表明,检测用支撑与实际用支撑两种结构在重力环境下支撑出的元件面形基本相同,面形相差0.0026nm(RMS);温控范围为0.05℃时,由机械结构热变形引起的镜体面形变化在0.001nm(RMS)量级。研究结果表明,运动学物镜元件支撑结构能够满足极紫外光刻系统对于物镜机械支撑结构的要求。