多原子分子的激光光电流效应和光谱

本文报导用CO_2选频激光器对CH_3Cl、CH_3OH、C_2H_5OH、C_2H_3Cl、C_2H_4、NH_3六种分子的光电流效应和光谱所做的研究.发现它们有很强的光电流效应.研究了放电管的V-I特性曲线和放电弛豫在光电流效应中的作用:初步讨论了这种效应的机构.实验结果还表明,红外区的激光光电流光谱术可以作为一种高分辨率光谱分析手段.     

问与答

<正> 什么是激光光电流效应?激光光电流效应有哪些应用? 当用激光照射气体放电管时,如果激光的频率和参与放电的粒子(原子、分子、离子)的某两个能级之     

脉冲光电流效应的机理研究

本文介绍一种用于脉冲激光激励空心阴极放电光电流效应的改进的表象理论,它以原子的能级集居数及电子密度变化的速率方程为基础,考虑到放电管内电子运动及电流回路方程获得了一组方程。该方程组很好地解决了脉冲光电流信号随电流、电压及激光光强的变化关系及时间特性(这一理沦提出了利用脉冲光电流效应测量某些低压气体等离子体参数的可能性)。     

光电流效应

一、引言当气体放电管受到光的辐照时,若光的频率与放电的粒子(原子、分子或离子)的某两个能级之间的跃迁频率相等,则放电管的宏观电参量(电压、电阻或电流)就会发生变化。这就是“光电流效应”。光电流效应的研究是由Penning于1928年开始的。他用一支氖放电管去照射另一支氖放电管,观察到放电管两端电压的变化。但是由于那时缺少高强度光源和微弱信号检测仪器,光电流效应又比较微弱,没有受到足够的重视。直到六十年代,由于强度高、单色性好的激光器的出现,尤其是可调谐染     

气体激光器辉光放电及弧光放电的观测

常见的霓虹灯管是最普通的放电管,它那鲜艳的红光是管中氖原子受到电子碰撞激发后所发射的。日常用的日光灯,实际上是汞蒸汽的辉光放电管。He-Ne激光器、CO_2激光器等也都是辉光放电,氩离子激光器虽然是弧光放电,但气压小的弧光则是从辉光放电过渡到大电流密度放电时形成的。工业     

用激光感生荧光技术研究Nels_2-2ρ反常光电流信号的机理

本文报道利用脉冲可调谐染料激光器在Ne HCD灯中测定Ne 1s_2-2p及1s_2-2p一高激发态跃迁的光电流信号的同时利用激光感生荧光技术测量Ne 2p-1s态的感生荧光信号,进一步研究Ne 1s_2-2p态反常脉冲光电流信号的机理。     

Ne空阴极放电中l_(S_2)-2p反常脉冲光电流信号的研究

本文报道利用YAG倍频激光泵浦的脉冲可调谐染料激光器在Ne-Nd空心阴极放电中测定Nels_2—2p态跃迁及ls_2-2p-5s′_1态二级级联跃迁的光电流信号实验,并介绍了我们对此进行的理论计算.结果表明,Ne ls_2—2p态跃迁的反常光电流信号起因不在于能级间粒子数反转.     

CWCO_2激光辐照下硅的光吸收特性

本文基于半导体材料硅(Si)中电子、空穴的费米统计分布,计算了Si对CO_2 激光的透射率随温度的变化,并用实验理论作了验证.说明在强CO_2激光辐照下,Si对CO_2激光能量有着强烈的吸收,其机理主要是自由载流子吸收.     

利用脉冲光电流效应测量相对gf数的研究

本文通过理论分析给出了脉冲光电流信号峰值与激励激光光强之间的定量关系.利用这一定量关系可以在放电管内能级集居数偏离Boltzmann分布及能级具有异常电离率的情况下利用光电流效应测定原子跃迁的相对gf数.用Nθ空阴极放电灯进行的判断实验测量的结果证实了这一方法的可行性.     

H_2对CO_2序列带激光的影响

本文研究了H_2对CO_2序列带激光的影响。研究结果表明H_2能大幅度提高序列带激光的小信号增益系数及其输出功率,并且H_2对序列带和常规带激光具有相似的影响。     

Magnetic ordering in HoRu2Si2, HoRh2Si2, TbRh2Si2 and TbIr2Si2 by neutron diffraction

Neutron diffraction study of polycrystalline HoRu₂Si₂, HoRh₂Si₂, TbRh₂Si₂, and TbIr₂Si₂ was performed in the temperature range between 4.2 and 300 K. For HoRu₂Si₂ the magnetic spin alignment of a linear transverse wave mode below the Néel temperature 19 K is observed. This static moment wave is propagating along the b-axis with k=(0, 0.2, 0) and is polarized in the c-axis. The root-mean-square and maximum saturation moments per Ho atom are 9.26 and 13.09μ_B, respectively. HoRh₂Si₂, TbRh₂Si₂ an TbIr₂Si₂ are simple collinear antiferromagnets of +-+- type with Néel temperatures of (27±1), (98±2) and (72±3) K, respectively. For TbRh₂Si₂ and TbIr₂Si₂ magnetic moments are localized on RE ions only and are aligned along the tetragonal axis, while for HoRh₂Si₂ they form an angle ø = (28±3)°.     

13C-selective IRMPD of CBr2F2/Cl2 and CCl2F2/Br2 systems

The CO₂ TEA laser irradiation of CBr₂F₂ in the presence of Cl₂ yielded ¹³C-enriched CBrClF₂ and ¹³C-enriched CCl₂F₂ under selected experimental conditions. As the photolysis proceeded, the ¹³C concentration of CBrClF₂ decreased gradually and that of CCl₂F₂ increased up to 90% or higher. These results can be explained by the mechanism involving the secondary ¹³C-selective IRMPD of the primary product CBrClF₂. On the other hand, the carbon-containing product for a CCl₂F₂/Br₂ system was only CBrClF₂; the further IRMPD of which probably regenerated CBrClF₂ in the presence of Br₂. The decomposition probabilities of ¹²C- and ¹³C-containing molecules in both systems were measured as functions of laser line, laser fluence, and reactant pressures.     

μ+SR study of LaNi2As2, URh2Si2 and CeRh2Si2

Muon spin relaxation experiments have been carried out in the paramagnetic and magnetically ordered states of URh₂Si₂ and CeRh₂Si₂. As the magnetic structure of these compounds is well known, these measurements can help to characterise their magnetic properties probed by μSR and to understand the μSR results of the heavy fermion compounds of the same crystallographic family. Our measurements show that the muons occupy two different crystallographic sites. The spectra of URh₂Si₂ and CeRh₂Si₂ in the magnetically ordered states are very different, probably reflecting their different magnetic structures. The spectra obtained on CeRh₂Si₂ are similar to the published spectra of the heavy fermion compound CeCu_2.1 Si₂. Muon spin rotation measurements on LaNi₂As₂ indicate that the muon is diffusing at 150 K.     

Eu2+掺杂CaSi2O2N2荧光粉发光性能

采用固相反应法合成了组成为Ca_1-xEu_xSi₂O₂N₂的Eu²⁺掺杂CaSi₂O₂N₂荧光粉.通过荧光光谱对样品的发光性能进行了研究,发现Eu²⁺掺杂CaSi₂O₂N₂荧光粉发射光谱为宽波段的单峰结构,主要包含绿光和黄光区,发射峰在556~568 nm.从发射光谱的宽带特征来看,CaSi₂O₂N₂:Eu²⁺的发射主要对应着Eu²⁺离子4f⁶5d→4f⁷跃迁.从激发光谱所覆盖的范围还可以看到,样品可以有效的被UV蓝-光激发,这意味着该类荧光粉在白光LED方面有可能得到广泛的应用.另外,样品的发光性能与激发离子的浓度有着很大关系.激发离子浓度增大时,发射光谱会发生明显红移.利用这一性质,可以通过改变Eu²⁺浓度来调节荧光粉的发光范围,从而满足不同场合的需要.同时,Eu²⁺浓度提高,样品发射光谱的强度也会随之增强,在x=0.06时发射强度达到最大值,之后继续增加Eu²⁺浓度,强度不仅没有增加反而降低,即出现浓度猝灭现象.     

Polar optic phonons in Hg2Cl2 and Hg2Br2

Far infrared (30–430 cm^?1) reflectivity measurements of Hg₂Cl₂ and Hg₂Br₂ single crystals have been performed in polarized light. The spectra, which are in agreement with group-theoretical predictions, were analyzed by the oscillator fitting procedure and Kramers-Kronig method. The results are compared with the existing data from other measurements and the large anisotropy of polar modes is briefly discussed. The polarization vectors of all long-wavelength symmetry modes were determined group-theoretically.     

Magnetostriction of SmMn2Ge2 and GdMn2Ge2 intermetallic compounds

Longitudinal and transverse magnetostrictions of polycrystalline samples of intermetallic compounds RMn₂Ge₂ (R=Sm or Gd) are measured in pulsed magnetic fields up to 250 kOe. It is found that linear magnetostrictive strains of about 10^?3 arise in a temperature range in which the magnetic field causes a change in the magnetic state of a manganese magnetic subsystem. The results obtained are described within the model of a two-sublattice ferrimagnet with a negative exchange interaction in the manganese subsystem in terms of a strong dependence of this interaction on interatomic distances.     

Superconductivity in LaPd_2Bi_2 with CaBe_2Ge_2-type structure

正Since the discovery of superconductivity in LaFeAsO_(1-x)F_x,the high-T_c iron-based superconductors have been extensively studied from both experimental and theoretical viewpoints [1-8]. However, the mechanism of the unconventional superconductivity is still to be resolved. To     

X-ray photoemission spectra measurements of CeNi2Sb2 and CeCu2Sb2

X-ray photoemission spectra, resistivity and susceptibility of CeNi₂Sb₂ and CeCu₂Sb₂ were measured and are discussed. The results indicate that these alloys are Kondo systems. For comparison of the valence band properties, the spectra of the isostructural alloys of RT₂X₂-type with R = La, Gd, T = Cu, Ni and X = Sn, Sb were investigated, too.