Accuracy design of ultra-low residual reflection coatings for laser optics

Refractive index inhomogeneity is one of the important characteristics of optical coating material, which is one of the key factors to produce loss to the ultra-low residual reflection coatings except using the refractive index inhomogeneity to obtain gradient-index coating. In the normal structure of antireflection coatings for center wavelength at 532 nm, the physical thicknesses of layer H and layer L are 22.18 nm and 118.86 nm, respectively. The residual reflectance caused by refractive index inhomogeneity(the degree of inhomogeneous is between -0.2 and 0.2) is about 200 ppm, and the minimum reflectivity wavelength is between 528.2 nm and 535.2 nm. A new numerical method adding the refractive index inhomogeneity to the spectra calculation was proposed to design the laser antireflection coatings, which can achieve the design of antireflection coatings with ppm residual reflection by adjusting physical thickness of the couple layers. When the degree of refractive index inhomogeneity of the layer H and layer L is-0.08 and 0.05 respectively, the residual reflectance increase from zero to 0.0769% at 532 nm. According to the above accuracy numerical method, if layer H physical thickness increases by 1.30 nm and layer L decrease by 4.50 nm, residual reflectance of thin film will achieve to 2.06 ppm. When the degree of refractive index inhomogeneity of the layer H and layer L is 0.08 and -0.05 respectively, the residual reflectance increase from zero to 0.0784% at 532 nm. The residual reflectance of designed thin film can be reduced to 0.8 ppm by decreasing the layer H of 1.55 nm while increasing the layer L of 4.94 nm.     

基于核函数的非线性分类相关分析及其在化学模式识别中的应用

与统计分析和神经网络相比,基于结构风险最小的支持向量机有更好的分类性能。它用于非线性分类时,先将样本映射到更高维的特征空间,往往会增加复共线性与冗余信息,将影响样本分布,降低线性支持向量机分类器(LSVC)的预测性能。本研究提出非线性分类相关分析算法(NLCCA),利用核函数技术,无需了解非线性映射的算式,从特征空间的样本映像中提取分类相关成分,以消除冗余信息,改善样本分布。由此构建的NLCCA-LSVC集成分类器具有优良的预测性能。经模拟数据的测试,并实际用于两个复杂的化学模式识别问题,均取得令人满意的效果,也印证了算法的有效性。     

基于预处理的决策树在化学数据挖掘中的应用

化学数据挖掘可从海量数据中提取蕴含的知识,决策树方法是一种重要的挖掘工具。鉴于决策树在处理连续数据上的局限性,本研究提出先进行预处理,将连续属性离散化,通过特征选择删除其冗余量,以此为基础构建决策树。该方法可防止决策树模型“过细”,使之具有良好的预报性能。将此方法应用于两个化学样品分类实例,效果良好。与贝叶斯分析和单一的决策树方法相比,其预报正确率有显著提高,且表达形式直观明确,易于理解和分析,适用于化学分类知识模式的挖掘。     

Ba-Sr系统激光感生碰撞能量转移的数值计算

以现有的激光感生碰撞能量转移的四能级理论模型为基础,通过直接积分态振幅的运动方程,对弱场、强场两种情况下Ba-Sr系统的激光感生碰撞能量转移过程进行了数值计算,得到了两种情况下的激光感生碰撞跃迁概率和碰撞截面的谱线线型.在弱场情况下的数值计算结果与近似解析解的计算结果符合很好.对强场情况下的数值积分计算结果表明：激光感生碰撞作用随转换激光强度的增大而增强;强场时激光感生碰撞截面谱线的峰值位置明显偏离了共振频率并向紫端移动,且碰撞截面谱线的半宽度(即调谐范围)较之弱场明显变小. 关键词： 激光感生碰撞能量转移 碰撞截面 Ba-Sr系统 强场     

Enhanced laser characteristics of pyrromethene 650 using modified PMMA as solid hosts

Solid-state samples based on modified polymethyl methacrylate (MPMMA) with methanol doped with the dye pyrromethene 650 (PM650) are prepared.The effects of a volume percentage of methanol on the laser characteristics of the sample,including spectra properties,slope efficiency,photostability and tunable properties,are investigated.The broadband dye laser output wavelength is around 655 nm and a highest slope efficiency of 32.23% is achieved.Pumping the samples at a repetition rate of 5 Hz with a pulse energy of as high as 100 mJ (the fluence is 0.26 J/cm 2),the longest lifetime (168000 shots) is obtained in the sample (MMA:methanol=18:2),and the corresponding normalized photostability reaches 109.19 GJ/mol.When the sample (MMA:methanol=18:2) is placed in a Shoshan-type oscilla-tor,the narrow-linewidth operation is a continuous tuning range (up to 64 nm).The results indicate that the laser characteristics of solid-state dyes can be greatly enhanced by using modified PMMA with methanol serving as the solid host.     

Valence orbital method of calculating harmonic emission from diatomic molecule

We present a valence orbital method of calculating high-order harmonic generation from a diatomic molecule with arbitrary orientation by using a space rotation operator. We evaluate the effects of each valence orbital on harmonic emissions from N₂ and O₂ molecules in detail separately. The calculation results confirm the different properties of harmonic yields from N₂ and O₂ molecules which are well consistent with available experimental data. We observe that due to the orientation dependence of \sigma and \pi orbitals, the bonding orbital (\sigma _{2pz} )^2 of N₂ determines the maximum of harmonic emission when the molecular axis of N₂ is aligned parallel to the laser vector, and the magnitude of the high harmonic signal gradually weakens with the orientation angle of molecular axis increasing. But for O₂ molecule the antibonding orbitals (\pi _{2py}^\ast )^1 and (\pi _{2pz}^\ast )^1 contribute to the maximum of harmonic yield when O₂ is aligned at 45^{\circ} and bonding orbitals (\pi _{2py} )^2 and (\pi _{2pz} )^2 slightly influence the orientation angle of maximum of harmonic radiation not exactly at 45^{\circ}.     

“电流的燮压”的教学

在谈到苏联学校的综合技术教育的内容时,列宁特别强调必须使学生深刻地认识电及其在国民经济各部门中的应用。列宁要求,中学毕业生“…应具有综合技术的眼界和基本的(初步的)综合技术训练。即: (1) 关于电的基本概念(正确规定的那些概念)。 (2) 关于机械工业上电的应用的基本概念。     

介紹北京市複雜儀器使用法的講演会

最近兩年來,北京市的普通中學和師範学校,在中央教育部的重點裝備和北京市教育局的大力配發教學设備的計劃下,均已獲得了自然科學各科教学所需的各種仪器、药品、模型和標本等;物理方面的演示儀器和學生實驗仪器以及實驗室中必備的設備等也都已逐步充實起來。絕大部分學校都已能够根據教學大綱,配合教学进行演示和学生分組實驗,加强了教学的直观性,貫澈理諭聯系實際的精神,因而教學质量也获得了一定的提高。伹由於許多教師,特别是青年教師,對一些比較複雜的物理     

由混合激发钠分子—原子系统产生的强度振荡变化的红外受激喇曼散射

本文报道以等频二步激发钠分子-原子系统,观测到强度随泵浦光的调谐而呈振荡变化的3P—4P受激喇曼散射,以及对应4D—4P和4F—3D跃迁的红外受激辐射和由四波混频产生的816.8～822.1nm区内可调谐相干辐射。文中对这些过程进行了分析讨论。     

初中二年級下學期物理课教师演示實驗

1.課本第112页第121圖的演示是很容易作的,不過遺應注意,音叉插入水中不可過深,最好使音叉与水面接近平行而稍微与水面接触,这样,水飛濺的時間較長並且濺出的距离较远,音叉振动的現象很明顯地表现出來。 2.演示圖122不必用鋼球,因鋼球不容易用線拴住,並且被音叉彈碰太猛烈。取軟木塞削成球狀用線穿過懸起試用,效果很好。也可用於演示圖123。 3.在演示圖126声音不能在真空裹傳播之前,首先應向学生說明抽氣機不能把罩内空氣抽出净尽,所以罩里不能達到真空。既然不是真空而有一些空氣存在所以声音仍然會傳播出來的,不過减弱罷了。因此,我們得不到完全