飞秒脉冲激光加热金属薄膜的理论和实验研究

超短脉冲激光加热可应用于研究材料中载能子之间的超快相互作用,同时也广泛应用于超快激光加工.此前人们提出的双温度模型和抛物一步模型都只能用于描述超短脉冲激光加热金属薄膜后热量传递过程的特定片段.基于双温度模型和傅里叶导热定律,提出普适的理论模型可用于完整描述飞秒激光加热金属薄膜/基底时的整个热量传递过程.同时在300 K温度下,采用背面抽运-表面探测瞬态热反射法实验研究了飞秒脉冲激光加热金属薄膜的热量传递过程,理论预测曲线和实验测量结果符合较好,验证了理论模型的正确性.基于此模型测量得到了金薄膜的电子-声子 关键词： 飞秒脉冲激光 电子-声子耦合 界面热导 瞬态热反射     

La_（2－x）Sr_xCu_（1－y）Fe_yO_4正常态的反常磁性

研究了Ｌａ２－ｘＳｒｘＣｕ１－ｙＦｅｙＯ４（ｘ＝０．１３，０．１５，０．１７和ｙ＝０．０，０．００２，０．００４，０．００６）多晶样品在不同磁场下（Ｈ＝１，３和５Ｔ）正常态直流磁化率与温度的关系和超导转变温度与Ｆｅ掺杂含量的关系．结果表明，不掺杂样品的正常态直流磁化率呈宽峰行为．随着Ｆｅ掺杂量的增多，直流磁化率与温度的关系由宽峰行为变为Ｃｕｒｉｅ－Ｗｅｉｓｓ行为．与此同时，超导转变温度随Ｆｅ掺杂含量的变化而变化．这表明载流子浓度是影响超导的重要因素．对Ｆｅ掺杂样品，其正常态直流磁化率与温度的关系可以用Ｘ＝ａ＋ｂＴ＋ｃ／（Ｔ－Ｔ０）很好的表示．我们认为，其中ａ＋ｂＴ项是带Ｐａｕｌｉ顺磁的贡献．对同一掺Ｆｅ样品，增加外磁场时，居里常数ｃ增大而常数项ａ减小．这是由于在Ｆｅｒｍｉ面存在不满的窄带（ｄｘ２上Ｈｕｂｂａｒｄ带），它是导致居里顺磁的原因．增加磁场时它往高能方向移动，窄带的电子空得更多，这些电子移向较宽的杂化带，导致每个Ｃｕ离子的磁矩增大，而带的Ｆｅｒｍｉ面电子态度减小．我们的实验结果也表明，超导电性与能带结构密切相关．     

飞秒激光脉冲作用熔石英的超快传热动力学研究

飞秒激光具有超短脉冲宽度、超高峰值功率的特点,飞秒激光与物质作用表现出的非线性吸收和低热扩散特性,使其在高精密微纳器件加工中有着重要的应用前景。建立了针对飞秒激光脉冲与熔石英作用的瞬态光电离以及非平衡传热的超快动力学模型。通过数值求解该模型获得了飞秒激光单脉冲作用熔石英的载流子密度和非平衡电子与声子温度的时空演化;得到了在非平衡态条件下,电声耦合时间随激光能量密度、脉冲宽度的近线性调控规律。进一步研究得到了瞬态电子热导、热容、电声耦合系数的变化规律,并对上述模拟现象进行了分析和探讨。     

La_（1．85）Sr_（0．15）Cu_（1－x）Fe_xO_（4－y）的窄能带行为与超导电性关系的研究

用ＳＱＵＩＤ直流磁强计研究了Ｌａ（１．８５）Ｓｒ（０．１５）Ｃｕ（１－ｘ）ＦｅｘＯ（４－ｙ）（ｘ＝０．００２，０．００４和０．００６）多晶样品在不同磁场下（Ｈ＝０．０１，０．０３，０．０５Ｔ）正常态的直流磁化率与温度关系和超导转变温度与Ｆｅ掺杂含量的关系．实验结果表明，不掺Ｆｅ的样品其直流磁化率与温度的关系里宽峰行为，随着Ｆｅ掺杂的增多，直流磁化率与温度的关系由宽峰行为迅速转变为Ｃｕｒｉｅ－Ｗｅｉｓｓ行为．与此同时，超导转变温度也由不掺Ｆｅ的３１．０Ｋ增加到３３．６Ｋ（ｘ＝０．００２），然后再单调降低．这清楚地表明，载流子浓度才是影响超导的最重要的因素。对于掺Ｆｅ的样品，其正常态直流磁化率Ｘ与温度Ｔ的关系可以用Ｘ＝ａ＋ｂＴ＋ｃ／（Ｔ一Ｔ０）很好地表示．我们认为，式中ａ＋ｂＴ项是由于Ｃｕｄ带泡利硕磁的贡献．增加磁场时，对于同一个接Ｆｅ样品，居里常数Ｃ增大而常数项ａ减小．这是由于掺Ｆｅ的样品在Ｆｅｒｍｉ面存在不满的窄带（ｄｘ２上Ｈｕｂｂｒｄ带），它是产生居里硕磁的原因．增加磁场时，它往高能量方向移动，窄带的电子空得更多，这些电子移向较宽的Ｃｕ杂化带．这样一来，增加磁场时，每个Ｃｕ离子的磁矩增大．而Ｃｕｄ带的Ｆｅ     

1．55μm InGaAsP／InP应变量子阱激光器的LP－MOCVD生长

本文首次报导了生长温度为５５０℃，以三甲基镓（ＴＭＧａ）和三甲基铟（ＴＭＩｎ）为Ⅲ族源，用低压金属有机物气相沉积（ＬＦＭＯＣＶＤ〕技术，高质量１．６２ｕｍ和１．３ｕｍＩｎＧａＡｓＰ及Ｉｎ０．５７Ｇａ０．４３Ａｓ０．９８Ｐ０．０４／Ｉｎ０．７３Ｇａ０．２７Ａｓ０．６Ｐ０．４量子阶结构的生长，并给出了１．５５ｕｍＧａＡｓＰ／ＩｎＰ分别限制应变量子阱结构激光器的生长条件，激光器于室温下脉冲激射，其阈值电流密度为２．４ｋＡ／ｃｍ２。     

少子陷阱特性和铍硅共注半绝缘GaAs空穴陷阱

用深能级瞬态谱（ＤＬＴＳ）技术测量了高温退火的Ｂｅ和Ｓｉ共注入的ＬＥＣ半绝缘ＧａＡｓ（无掺杂）。在多子脉冲作用下的Ａｌ／Ｂｅ－Ｓｉ共注ＬＥＣＳＩＧａＡｓ肖特基势垒中，观测到Ｅ₀₁（０．２９８），Ｅ₀₂（０．３４１），Ｅ₀₃（０．５５５）和Ｅ₀₄（０．８２１）等四个电子陷阱以及两个主要的少子（空穴）陷阱Ｈ＇₀₃（０．５４）和Ｈ″₀₃（０．５７）。两少子陷阱的ＤＬＴＳ信号具有若干特点，比如它们的ＤＬＴＳ·峰难于通过增宽脉冲达到最大高度；以及峰的高度强烈地依赖于温度等。这些现象可以用少子陷阱的少子俘获和热发射理论进行合理地解释。鉴于用ＤＬＴＳ技术测量这种陷阱的困难，我们用恒温电容瞬态技术测定它们的空穴表观激活能分别为０．５４和０．５７ｅＶ。它们是新观测到的和Ｂｅ－Ｓｉ共注ＳＩＧａＡｓ有关缺陷。 关键词：     

铂Hugoniot曲线的Ab initio计算

对于一个原子平均体积为Ｖ,温度为Ｔ的热力学系统,体系的Ｈｅｌｍｂｏｌｔｚ自由能可以写为Ｆ（Ｖ,Ｔ）＝Ｅｃ（Ｖ）＋Ｆｉｏｎ（Ｖ,Ｔ）＋Ｆｅｌ（Ｖ,Ｔ）＋Ｆｍａｎ（Ｖ,Ｔ）其中Ｅｃ为０－Ｋ冷能。对于其中的电子热激发贡献Ｆｅｌ,目前流行的有三种计算方案,即：Ｍｏｒｕｚｚｉ的Ｄｅｂｙｅ－Ｇｒｕｅｎｅｉｓｅｎ方案、Ｍｏｒｉａｒｔｙ的ＭＧＰＴ方案和Ｗａｓｓｅｒｍａｎ的ＣＥＬＬ模型方案。Ｄｅｂｙｅ－Ｇｒｕｅｎｅ     

光激电流谱的测试

用光激瞬态电流谱ＯＴＣＳ（ｏｐｉｔａｌｔｒａｎｓｉｔｉｏｎｃｕｎｅｎｔｓｐｅｃｔｒｏｓｃｏｐｙ）方法对ＩｎＰ∶Ｆｅ进行了初步测试。目的是研究半绝缘ＩｎＰ∶Ｆｅ中的深能级，了解其作为光电器件、高速器件衬底的稳定性。在低温下，用强光发现半绝缘ＩｎＰ∶Ｆｅ中存在两深能级，分别是ＥＴ＝０．３４ｅＶ的电子陷阱和ＥＴ＝１．１３ｅＶ的空穴陷阱。     

磁转变对La0.7Ca0.3MnO3在Tc附近的输运性质的影响

测量了Ｌａ０．７Ｃａ０．３ＭｎＯ３的热导和电阻，温度范围为７７－３００Ｋ，在２６０Ｋ，观察到电阻曲线上的金属－半导体转变上的，热导曲线上有一个不大的斜率的变化。同时不发现在热导单调光滑下降曲线上２２０－２６０Ｋ热导有增加，电阻在２４０Ｋ有斜率的变化，我们讨论了这两种输运性质，认为这与材料在ＴＣ附近复杂的磁行为相联系。     

Hg0.9Tl0.1Ba2Ca2Cu3O8＋δ超导膜（Tc〈124K）在混合态中的输运？…

本文研究了ｃ轴取向的Ｈｇ０．９Ｔｌ０．１Ｂａ２Ｃａ２Ｃｕ３Ｏ８＋δ超导膜（Ｔｃ〉１２４Ｋ）在混合态下的电阻展宽及霍尔效应。低电阻区域的展宽显示出热激活磁通蠕动行为。在膜的超导转变温度以下,我们观察到霍尔电阻率符号反常现象。霍尔电阻率（ρｘｙ）和纵向电阻率（ρｘｘ）具有ρｘｙ（Ｔ）＝ｋρｘｘ＾β（Ｔ）的标度关系。     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Improvement of four-wave mixing-based wavelength conversion efficiency in dispersion shifted fiber by 40-GHz clock pumping

40-GHz clock modulated signal as a pump to improve the efficiency of four-wave mixing (FWM)-based wavelength conversion in a 26.5-km dispersion shifted fiber (DSF) is investigated. The experimental results demonstrate that the conjugated FWM component has higher intensity with the clock pumping than that with the continuous-wave (CW) light pumping. The improvement of FWM-based wavelength conversion efficiency is negligible when the pump power is less than Brillouin threshold. But when the pump power is greater than Brillouin threshold, the improvement becomes significant and increases with the increment of pump power. The improvement can increase up to 9 dB if pump power reaches 17 dBm.     

Characterization of PolyA and PolyC mismatches by Raman spectroscopy

A.C mismatches are studied by Raman spectral characterization of PolyA, PolyC, and their equimolar complex in solution of 0.14 mol/L Na ,pH7.0.Experimental results show that A·C mismatches occur to be A/B (mainly A) conformers, and unlike Watson-Crick base pairing, this kind of mismatches is stabilized by only one hydrogen bond involving cytosine N4H2 and adenine N7.The formation of A·C complex makes the base stacking interactions much stronger, and conformation of the backbone more ordered, which leads to obvious Raman hypochromic effect with some shifts in corresponding bands.