从薄膜波导传播衰减的角度研究光学薄膜的损耗:(Ⅱ)实验分析

本文从实验的角度介绍从薄膜导波传播衰减研究光学薄膜损耗的方法,并以一些低损耗的光学薄膜样品的测量结果说明这种方法对损耗研究的灵敏程度及其优越性.     

用后向散射压缩器产生超高强度激光

报道自制的一台小型的激光系统,用后向布里渊散射与光栅压缩系统组合,把5ns激光脉冲压缩到40ps,压缩率大于100倍.     

CARS difference spectroscopy

Summary In this paper we present a vibrational-spectroscopy technique which combines the advantages of coherent anti-Stokes Raman spectroscopy (CARS) and linear Raman difference spectroscopy. The method which we call CARS difference spectroscopy can be applied for the study of small frequency shifts and/or bandwidth changes in the CARS spectra of liquid mixtures and solutions. First we develop the theory necessary for the interpretation of experimental data obtained from CARS difference measurements of mixtures of two Raman-active liquids and present some model calculations for benzene-toluene mixtures of different concentrations. Then the experimental arrangement used for CARS difference measurements as well as some examples of recorded spectra are described. We show that it is possible to observe the effects of dilution on CARS spectra with high accuracy by applying the discussed technique. Paper presented at the “XI European CARS Workshop”, Florence, Italy, 23–25 March, 1992.     

Deuteron size effects on its elastic scattering from1H and4He

The effect of change in deuteron size on its elastic scattering from protons and alphas is investigated by varying the Hulthen parameters of the deuteron wave function in the scattering process. The cross sections forp-d scattering, calculated in the Born approximation, are found to increase substantially at backward angles even when the deuteron size is reduced by a small amount, whereas the shape of the angular distribution does not change significantly. For theα-d elastic scattering, interaction potential is obtained by folding the deuteron wave function and the optical potential for nucleon-scattering. The cross sections calculated atE _d = 13·7 MeV, shows that the first minimum around Θ_cm = 60° is deepend as the deuteron size is reduced, while at 52 MeV bombarding energy, the size effects are not very distinct. These observations are useful in the interpretation of deuteron cluster knockout reactions.     

Phonon dispersion in aluminium arsenide and antimonide

The phonon dispersion curves for aluminium arsenide and antimonide have been investigated by using a deformation bond approximation model. The results obtained from this model are compared with the experimental values wherever it is available. Since there is no complete experimental phonon dispersion curves for AlAs, we could not compare our calculated results, but the results of AlSb have been compared with the inelastic neutron scattering measurements at 15 K. However, we compare the phonon frequencies of AlAs and AlSb at critical points of the Brillouin zone obtained by our calculations and Raman spectroscopy measurements. This model predicts the phonon modes satisfactorily in all the symmetry directions of the Brillouin zone (BZ). The spectrum has similar features as observed in other III–V compound semiconductors.     

Study of metal containing hydrogenated carbon films by STM/AFM and SAXS

Metal-containing amorphous hydrogenated carbon films are of high interest for industrial applications because of their excellent frictional properties, their high abrasive wear resistance and their electrical conductivity, which can be adjusted in a range of 10–12 orders of magnitude. In order to get insight into the mechanical and electrical properties it is necessary to study the nanostructure of the films. The structure consists of small nanometer sized metallic or carbidic particles, which are embedded in a three dimensional amorphous hydrogen-carbon matrix. Anomalous small angle X-ray scattering (ASAXS) and scanning tunneling microscopy (STM) have been used to determine size- and distance-distributions of the particles as a function of metal content. Problems and restrictions of both methods will be discussed. Furthermore the capabilities of scanning probe techniques to distinguish different materials on a nanometer scale (material contrast) have been studied employing barrier height imaging (dI/dz) and friction force microscopy.Dedicated to Professor Dr. rer. nat. Dr. h. c. Hubertus Nickel on the occasion of his 65th birthday     

中子与90,91,92,94Zr反应的理论计算和分析

根据中子与天然Zr及其同位素反应的总截面,去弹截面和弹性散射角分布的实验数据,得到一组普适的光学模型势参数;应用得到的光学模型势参数,光学模型,Hauser-Feshbach理论,预平衡反应的激子模型和扭曲波玻恩近似理论,系统计算和分析了中子与^90,91,92,94Zr反应的非弹散射角分布和双微分截面,理论结果与实验很好的一致.     

Surface and subsurface oxide formation on Ni(1 0 0) and Ni(1 1 1)

The oxidation of Ni(1 0 0) and Ni(1 1 1) at elevated temperatures and large oxygen exposures, typical of the methods used in the preparation of NiO(1 0 0) films for surface studies, has been investigated by medium energy ion scattering (MEIS) using 100 keV H⁺ incident ions. Oxide film growth proceeds significantly faster on Ni(1 1 1) than on Ni(1 0 0), but on both surfaces oxide penetration occurs to depths significantly greater than 100 Å with total exposures of 1200 and 6000 L respectively. The metal/oxide interface is extremely rough, with metallic Ni extending to the surface, even for much thicker oxide films on Ni(1 1 1). On Ni(1 1 1), NiO growth occurs with the (1 0 0) face parallel to the Ni(1 1 1) surface and the close-packed 〈1 1 0〉 directions parallel. On Ni(1 0 0) the MEIS blocking curves cannot be reconciled with a single orientation of NiO(1 0 0) (with the 〈1 1 0〉 directions parallel) on the surface, but is consistent with the substantial orientational disorder (including tilt) previously identified by spot-profile analysis LEED.     

A polarised SUSANS facility to study magnetic systems

Using a right-angled magnetic air prism, we have achieved a separation of ～10 arcsec between ～2 arcsec wide up and down-spin peaks of 5.4 Å neutrons. The polarised neutron option has thus been introduced into the SUSANS instrument. Strongly spindependent SUSANS spectra have been observed over ±1.3 × 10^?4 Å^?1 range for several magnetic alloy samples. Spatial pair-distribution functions for the up and down-spins as well as the nuclear and magnetic scattering length density distributions in the micrometer domain, have been deduced from these spectra.     

Small-angle neutron scattering studies on water soluble complexes of poly(ethylene glycol)-based cationic random copolymer and SDS

The interaction of cationic random copolymers of methoxy poly(ethylene glycol) monomethacrylate and (3-(methacryloylamino)propyl) trimethylammonium chloride with oppositely charged surfactant, sodium dodecyl sulphate, and the influence of surfactant association on the polymer conformation have been investigated by small-angle neutron scattering. SANS data showed a positive indication of the formation of RCPSDS complexes. Even though the complete structure of the polyion complexes could not be ascertained, the results obtained give us the information on the local structure in these polymer-surfactant systems. The data were analysed using the log-normal distribution of the polydispersed spherical aggregate model for the local structure in these complexes. For all the systems the median radius and the polydispersity were found to be in the range of 20 ± 2 Å and 0.6 ± 0.05, respectively.