Papers by Keyword: Extinction Coefficient

Abstract: The review article focuses on the growth of thin film and its characterization by UV-Vis-NIR spectroscopy. For UV-Vis-NIR spectroscopy of thin films, they are usually deposited on translucent quartz glass surfaces. The article reports the extraction of various thin film optical parameters viz., absorption coefficient (α), Urbach energy (E_u), optical band gap (E_g), refractive index (n), extinction coefficient (k), dielectric constants, dissipation factor (tanδ) and optical conductivity (σ_optical) by using optical spectra (absorption(A)/transmittance (T)/reflectance (R)). Furthermore, the effect of thin film substrate temperature (T_s) and/or thickness (d) and/or post-deposition annealing temperature (T_a) on various optical parameters is discussed in detail.

Abstract: Ellipsometry is a non-destructive and indirect technique able to characterize both optical and dielectric properties of thin films and bulks, besides determining the thickness of thin films. This characterization is performed by evaluating the change in the polarization state of the incident light when it interacts with the material of interest. In this work, the ellipsometry technique was used to characterize optical properties of AZ31 magnesium alloy samples. This alloy has several interesting properties such as low density, high thermal conductivity, good machinability, among others, which makes it suitable for use in automotive and aerospace components. However, when this alloy is exposed to ambient atmosphere, it undergoes natural oxidation, developing a surface film of oxides and/or hydroxides. This study aimed to establish an efficient methodology for accessing the optical and dielectric characteristics of the substrate (AZ31 alloy) as well as those for the surface film of oxide/hydroxides, and to obtain the thickness of this film. Four samples mechanically grinded and polished were investigated: One sample, namely P sample, was subjected to the ellipsometric measurements immediately after grinding and polishing and three samples, namely A10, A50 and A60, were exposed to the air at 150°C during 10, 50 e 60 minutes, respectively. From the results of the ellipsometric measurements for P sample, it was possible to determine the refractive index (n) and extinction coefficient (k) curves as a function of the wavelength (λ) for the substrate (AZ31 alloy). Besides, through appropriate modeling, it was possible to determine the thicknesses of the oxides/hydroxides films presented in A10, A50 and A60 samples. The thicknesses values obtained seem to be quite coherent when we analyze the surface roughness of these samples using the confocal microscope, validating the optical model constructed to represent the A10, A50 and A60 samples. The results achieved in this study can contribute to the study of both of oxides/hydroxides layers growth and protective coating films growth for AZ31 magnesium alloy.

Abstract: The vertical distribution of aerosol extinction coefficients, and relativity between aerosol and BC the within summer planetary boundary layer (PBL) over the observation site are shown in this paper. The data indicates that the aerosol is almost trapped within PBL and troposphere layer is rather stable and the main composition of aerosol in Beijing is BC. The multi-layer structure of the aerosol distribution is obvious.

Abstract: Perylene dicarboximide dimer with electron withdrawing groups were synthesized and fully characterized by ¹H-NMR and ¹³C-NMR spectra. The effects of the substituted groups on the optical and electrochemical properties of the two compounds were investigated. The ∏-∏* absorption peak of the perylene dicarboximide dimer compounds were red shifted from 525nm to 535nm. The band gaps of the dimer could be tuned from 2.28 eV to 2.13 eV. The first reduction wave of the dimer with electron withdrawing groups is shifted by 60 mV to more positive potential compared to that of perylene dicarboximide, suggesting the enhanced electron affinity. Furthemore, the dimer exhibited intermolecular aggregation, and decrease fluorescence quantum yield.

Abstract: Lidar is the main standoff detection system against bioagent/bioaerosol, An infrared lidar has been developed for bioagent/bioaerosol monitoring. The overall architecture and specifications of the lidar were described. The results of overlap coefficient, horizontal and slant measurements at Hefei, such as comparison of observed horizontal extinction coefficients between commercial MPL Lidar and the IRLidar, the slant path time-space extinction coefficient distributions have been revealed and discussed. The results show that the IRLidar is a reliable lidar with advanced performances.

Abstract: The vertical distribution of aerosol extinction coefficients within winter planetary boundary layer (WPBL) over the observation site are shown in this paper, and the heights of PBL are discussed. The data indicates that the aerosol over the measurement site is almost trapped within PBL and troposphere layer and is rather stable, and the multi-layer structure of the aerosol distribution is obvious.

Abstract: In this paper, we use Bruggeman model to calculate refractive index of nanoporous silicon, which was fabricated by electrochemical etching. The calculated result shows that the refractive index of the nanoporous silicon decreases linearly with increasing porosity and etching current density. In addition, the refractive index of nanoporous silicon was also measured by spectroscopic ellipsometry in the visible light spectrum range. The measured refractive index and extinction coefficient were in agreement with the calculated data, after being modified by the refractive index modified model of heavily doped silicon. In particular, we estimate the refractive index at the optical wavelengths in visible and near-infrared spectrum ranges, which may be widely used in various types of optical sensors and optoelectronic devices for optical communication systems.

Abstract: The transmittance spectrograms of quartz glass slabs are measured in spectral range 1.34-4.20μm. A new inversion method of optical constants (k is extinction coefficient and n is refractive index) of glass was proposed to calculate the optical constants. The optical constants of selenide glass attained in the references were selected as the true values, and the spectral transmittance radio of the semitransparent solid based on the direct model simulation were regarded as the experimental values, and validation of the new inversion method was investigated. Then the optical constants of quartz glass were achieved by the inverse model.

Abstract: The two flux approximation model is usually used to calculate the heat transfer of radiation for porous materials. In this paper, the parameters identification method of the extinction coefficient and the albedo of scattering in the two flux model is set up by using the identification theory according to the data of the back temperature. The simulated process shows that the convergence rate is fast and the results by the parameters identification are very close to the origin values.

Abstract: This paper has introduced the concept of complex refractive index and studied the effects of material absorption on the total reflection tunneling characteristics of photonic crystals by employing the characteristic matrix method. Through numerical computation, changes of the total reflection tunneling peak of photonic crystals along with the extinction coefficient and periodical optical thickness of the materials have been studied. The peak height of the total reflection tunneling decreases with the increase of the extinction coefficient, while the frequency of the total reflection tunneling peak is free from the extinction coefficient. Moreover, the frequency and bandwidth of the total reflection tunneling decrease with the increase of the periodical optical thickness.