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161.
Using a neutral N2 beam as target,this paper studies the dissociation of N2+ in intense femtosecond laser fields(45 fs,~1×10 16 W/cm 2) at the laser wavelength of 800 nm based on the time-of-flight mass spectra of N + fragment ions.The angular distributions of N+ and the laser power dependence of N + yielded from different dissociation pathways show that the dissociation mechanisms mainly proceed through the couplings between the metastable states(A,B and C) and the upper excited states of N2+.A coupling model of light-dressed potential energy curves of N+2 is used to interpret the kinetic energy release of N+. 相似文献
162.
163.
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. 相似文献
164.
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}. 相似文献
165.
166.
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. 相似文献
167.
168.
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 总被引:1,自引:0,他引:1
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。 相似文献
169.
170.
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 相似文献