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This paper experimentally and theoretically examines the scattering properties of simulated non-spherical hydrometeors including water oblates, ice oblates and ice sphere–cone-oblates, in terms of the backscattering cross-section and the differential reflectivity. The experimental measurements of the backscattering cross-sections of non-spherical hydrometeor samples were performed in the Electromagnetic Scattering Laboratory of China National Space Industrial Corporation. Meanwhile, the backscattering cross-sections have been computed with the transition (T) matrix method. The theoretical results are compared with the experimental data, showing that the calculations are consistent with the observations in general. Experimental and theoretical analyses indicate that the backscattering cross-section of non-spherical particles increases as the particle size parameter increases, and fluctuates when the sizes are larger under the effect of resonance scattering. Differential reflectivity Z DR of water oblates in natural rainfall is always greater than 0 dB whereas Z DR of hailstones may be negative. There is a good linear relationship between differential reflectivity and aspect ratio of a particle. These derivations agree with the literature and can be used to identify the presence of hail particles and distinguish between plate-type and columnar-type hydrometeors. In this study, the measuring experiment and the T-matrix method calculations for the scattering of simulated raindrop and ice particles are also briefly described.

We have carried out an ultrafast time-resolved differential reflectivity study of a ferromagnetic semiconductor InGaMnAs and made a systematic comparison with low-temperature grown and high-temperature grown InGaAs reference films. Very short carrier lifetimes (∼2 ps) were observed in InGaMnAs and the low-temperature grown InGaAs film, but not in the high-temperature grown InGaAs film. We attribute the short lifetimes to carrier trapping by mid-gap states introduced during low-temperature MBE growth. Furthermore, at long times, we observed periodic oscillations in the differential reflectivity signal with period ∼20 ps, which we interpret as coherent acoustic phonons.

Hail is the most frequent damaging phenomena affecting northern Italy during severe weather. At the Servizio Meteorologico Regionale of the Emilia-Romagna region the analysis of the differential hail signal HDR (Aydin et al., 1986), which is a function of horizontal reflectivity and differential reflectivity, was carried out and checked against the ground truth coming from a dense hail pad network. That study, which used the data related to four hailstorms occurred in 1997, allowed the implementation of an operational technique since early summer of 1998. Since then, an automatic hail detection algorithm runs during the stormy season (March through October) with the issue of a hail warning for nowcasting purpose. The performance of such an automatic method is investigated in an operational and statistical perspective. First results highlight the difficult in correctly estimating the position of a hail shaft with respect to the coarse resolution of the pad network, e especially when hailstorms of small extension are involved.

Surface differential reflectivity and surface sensitive electron spectroscopies have been applied to study the optical properties of CdTe(110) surface. The comparison of the results acquired for the surfaces prepared by two different methods (cleavage and Ar + ion sputtering) enabled us to propose a model explaining the experimental results in a coherent way.

Optical transitions between surface state bands have been detected on the Si(111)-Pb(√3 × √3) mosaic phase by means of surface differential reflectivity (SDR) in the energy range between 1.3 and 3.8 eV. The SDR spectrum, obtained between the clean and the hydrogenated surface, presents a broad structure in this energy range with a maximum at 3.0 eV. The spectrum has been deconvolved into three Gaussian singlets at energies 1.8, 2.5 and 3.05 eV. These transitions have been, tentatively, assigned to different points in the surface Brillouin zone. No contribution from the hydrogenated surface is expected, as observed by angle resolved photoemission.

The electronic structure of Cu 3 Si is calculated with a self-consistent scalar relativistic linear muffin tin orbitals code in the atomic sphere approximation. The results are compared to UPS and differential reflectivity measurements on the reacted CuSi interface layer where Cu 3 Si formation is generally admitted. Both theoretical and experimental results show a shift of the d band towards lower energies with respect to pure Cu. The disappearance of a sharp absorption edge at 2.1 eV in differential reflectivity is related to the broadening of the Cu d band due to Si p-Cu d hydridization as shown by the calculation.

Electron spectroscopies (photoemission (UPS) and Auger electron spectroscopy (AES)) together with the surface differential reflectivity (SDR) have been applied to observe and identify optical transitions between surface related states on CdTe(110) surfaces. The contributions to the band of optical transitions have been revealed at the photon energies of 2.9, 3.5, and 3.9 eV. Their correspondence to excitations from the occupied S1 band to the unoccupied U1 one at the Γ, X and, X′ points of the surface Brillouin zone is discussed. Dependence of the surface optical properties of CdTe(110) surfaces on cleavage quality and oxidation procedure are analysed, too.

Surface differential reflectivity experiments with polarised light have been carried out for cleaved and then oxidised CdTe(110) surfaces. It was shown that the optical anisotropy of the surface investigated is small and almost independent from photon energy. The interpretation of the spectra in terms of optical transitions between surface states is discussed.

The optoelectronic compounds of GaAs and ZnSe are difficult to analyze by PIXE (particle-induced X-ray emission) due to the strong absorption of the As and Se K α X-rays. As part of a program to investigate optoelectronic materials using ion beam techniques, we have explored the possibility of using the high sensitivity of PIXE to check these materials for stoichiometry and dopant concentrations. The K α X-ray intensity ratios of Ga to As and Zn to Se have been investigated using H beams of 0.5 to 2.5 MeV and He beams of 1.0 to 2.5 MeV. The variation in the X-ray intensity ratio with beam energy and target thickness is modelled in terms of the cross section for X-ray production and the absorption coefficients of the X-rays in the target. The results of this model show the experimental conditions that must be satisfied in order that the X-ray intensity ratios are not strongly affected by X-ray absorption; and therefore, the conditions necessary for accurate analysis. To demonstrate this, four 1 μm Al x Ga 1− x As-on-GaAs samples were analyzed and gave results in agreement with those obtained by differential reflectivity.

The roughness of Si(111) surfaces induced by heating at temperatures between 900 and 1000°C is studied by differential reflectivity measurements. For the lowest temperatures, the stepped-roughness of the surface is smoothed out by annealing the surface, leading to an increase of reflectivity for light energies below 3 eV. For the highest temperatures, a larger scale roughness (of the order of several tens of nm) is formed at the surface. This roughness increases with temperature and induces essentially a scattering of light leading to a decrease of reflectivity in the UV range.

We report the transient differential reflectivity ΔR/R in Y 1−x−y Pr x Ca y Ba 2 Cu 3 O 7 thin films. The transient differential reflectivity measurement reveals that the effect of Pr substitution for Y ions on the related Fermi level position is similar to that of the oxygen deficiency in YBa 2 Cu 3 O 7-δ system, however, it is different from the effect of divalent Ca substitution for Pr.

New accurate surface differential reflectivity data of the GaAs and GaP cleavage faces are presented. Surface state transitions have been detected near 2.9 eV in GaAs(110), while in GaP(110) they appear at 2.8 and 3.5 eV. In both cases a small bulk-like Franz-Keldish effect is superimposed on the surface contribution to differential reflectivity. A method for subtracting this term out is described. The relevance of the present results in the context of the debate on surface excitons is also discussed.

The optical properties of rough Ag films quenched on substrates cooled to 150 K are studied by differential reflectivity during annealing to room temperature. An abnormal optical absorption at about 2.5 eV is assigned to surface roughness.

We compute the optical properties of semiconductor surfaces starting from the self-consistent electronic structures determined using local pseudopotentials with a plane-wave basis set. Calculations for a 9 layer (110) slab of GaP are carried out with both clean and H covered surfaces. Differential reflectivity spectra and their anisotropies are interpreted in terms of transitions involving surface states.

The optical properties of the GaAs(110) surface are studied by means of self-consistent local-density slab calculations. It is found that a large contribution to the calculated anisotropy of the clean surface reflectance is related to transitions which do not involve surface states. Comparison is made with differential reflectivity and reflectance anisotropy experiments.

We present a determination of surface dielectric functions (SDF) of Si(111)2×1, Ge(111)2×1, GaAs(110) and GaP(110) surfaces obtained using polarized surface differential reflectivity (SDR) technique.

The results of reflectivity and differential reflectivity measurements at non-normal incidence for p-polarized light of thin films of silver on different substrates are presented. It was found that the peak associated with the silver plasma frequency broadens and shifts towards higher energies for thinner layers. A model of a thin layer with bulk silver optical constants cannot be used to explain this behaviour. Agreement with experiment is obtained if we take into account not only the shorter relaxation time of the free electrons but also the non-local effects associated with the longitudinal wave (polarization wave) near the plasma frequency (in our configuration these effects are particularly important).

From the measured differential reflectivity of W(Fe) alloys with Fe-concentrations up to 1.6 at % the energy dependence of the change of the imaginary part of the dielectric constant in the range 0.5–5.5 eV has been calculated. The results are discussed in terms of the change of the electronic states due to the formation of a solid solution and localized states.

We present results on the polarization dependence of Surface Differential Reflectivity in GaP(1 1 0) and GaAs(GaAs(1 1 0) surfaces. GaP(1 1 0) shows a transition at 2.8 eV which is excited only with the light electric vector parallel to the [1 1 0] direction; for the optical transition above 3.0 eV there is not any marked polarization dependence. GaAs(1 1 0) shows optical transitions between 2.6 and 4.0 eV which have a weak dependence on light polarization.