Optical Properties Of Different Types Research Articles

Investigation on the valence state stability and optical properties of Mg2GeO4:Cr

In this work, the valence states and optical properties of chromium-doped Mg2GeO4 are investigated via first-principles methods. The formation energies and thermal charge transition levels show that the site occupation and valence states of chromium are strongly related to the growth condition: Cr3+ dominates in the Mg sites under Mg-poor conditions, and Cr4+ dominates in the Ge sites under Ge-poor conditions. With the lithium co-doping, the Fermi-level is pinned below the midgap, and the formation energies of chromium-doped Mg sites become the lowest either Mg-poor or Ge-poor conditions, suggesting that the co-doping of lithium ions promotes the chromium to preferentially occupy Mg sites, in good agreement with experiments. Furthermore, the excitation and emission processes of chromium ions are investigated, and our results recommend that the near-infrared emission is related to the 4T2 to 4A2 transition of Cr3+ at the Mg sites and the infrared emission is related to the 3T2-3A2 transition of Cr4+ at the Ge site. Our results help to understand the stability of the valence states of chromium ions doped Mg2GeO4 and the effects of ions co-doping in regulating the chromium valence states, as well as the corresponding optical properties of different types of chromium ions.

Optical Properties of Au-Ag Bimetallic Nanoparticles of Different Shapes for Making Efficient Bimetallic-Photonic Whispering Gallery Mode Hybrid Microresonators

For the first time, we propose a bimetallic-photonic whispering gallery mode (WGM) hybrid microresonator for the detection and sizing of single protein molecules in real time. To optimize the sensitivity of hybrid microresonators, theoretical simulations have been carried out to understand the optical properties of different types of Au-Ag bimetallic nanoparticles such as solid nanospheres, dielectric core-bimetallic nanoshells, nanostars, and nanoprisms using Lorenz-Mie theory, Aden-Kerker theory, and finite element method (FEM). The role of size and Au-Ag ratio on the optical properties of the nanospheres and nanoshells has been studied. In addition, the effect of the Au-Ag ratio on the optical properties of nanostars and nanoprisms has been investigated. The local electric field intensity enhancement values of bimetallic nanostructures of different shapes have been estimated using the FEM. Finally, the advantages of the bimetallic-WGM hybrid microresonator as compared to the monometallic-WGM hybrid microresonator have been explained in detail.

Chalcogenide Microstructured Optical Fibers for Mid-Infrared Supercontinuum Generation: Interest, Fabrication, and Applications

The mid-infrared spectral region is of great technical and scientific importance in a variety of research fields and applications. Among these studies, mid-infrared supercontinuum generation has attracted strong interest in the last decade, because of unique properties such as broad wavelength coverage and high coherence, among others. In this paper, the intrinsic optical properties of different types of glasses and fibers are presented. It turns out that microstructured chalcogenide fibers are ideal choices for the generation of mid-infrared supercontinua. The fabrication procedures of chalcogenide microstructured fibers are introduced, including purification methods of the glass, rod synthesis processes, and preform realization techniques. In addition, supercontinua generated in chalcogenide microstructured fibers employing diverse pump sources and configurations are enumerated. Finally, the potential of supercontinua for applications in mid-infrared imaging and spectroscopy is shown.

The optical properties, physical properties and direct radiative forcing of urban columnar aerosols in the Yangtze River Delta, China

Abstract. The optical and physical properties as well as the direct radiative forcings (DRFs) of fractionated aerosols in the urban area of the western Yangtze River Delta (YRD) are investigated with measurements from a Cimel sun photometer combined with a radiation transfer model. Ground-based observations of aerosols have much higher temporal resolutions than satellite retrievals. An initial analysis reveals the characteristics of the optical properties of different types of fractionated aerosols in the western YRD. The total aerosols, mostly composed of scattering components (93.8 %), have mean optical depths of 0.65 at 550 nm and refractive index of 1.44 + 0.0084i at 440 nm. The fine aerosols are approximately four times more abundant and have very different compositions from coarse aerosols. The absorbing components account for only ∼ 4.6 % of fine aerosols and 15.5 % of coarse aerosols and have smaller sizes than the scattering aerosols within the same mode. Therefore, fine particles have stronger scattering than coarse ones, simultaneously reflecting the different size distributions between the absorbing and scattering aerosols. The relationships among the optical properties quantify the aerosol mixing and imply that approximately 15 and 27.5 % of the total occurrences result in dust- and black-carbon-dominating mixing aerosols, respectively, in the western YRD. Unlike the optical properties, the size distributions of aerosols in the western YRD are similar to those found at other sites over eastern China on a climatological scale, peaking at radii of 0.148 and 2.94 µm. However, further analysis reveals that the coarse-dominated particles can also lead to severe haze pollution over the YRD. Observation-based estimations indicate that both fine and coarse aerosols in the western YRD exert negative DRFs, and this is especially true for fine aerosols (−11.17 W m−2 at the top of atmosphere, TOA). A higher absorption fraction leads directly to the negative DRF being further offset for coarse aerosols (−0.33 W m−2) at the TOA. Similarly, the coarse-mode DRF contributes to only 13.3 % of the total scattering aerosols but > 33.7 % to the total absorbing aerosols. A sensitivity analysis states that aerosol DRFs are not highly sensitive to their profiles in clear-sky conditions. Most of the aerosol properties and DRFs have substantial seasonality in the western YRD. The results further reveal the contributions of each component of the different size particles to the total aerosol optical depths (AODs) and DRFs. Additionally, these results can be used to improve aerosol modelling performance and the modelling of aerosol effects in the eastern regions of China.

TiO2 synthesized by various routes and its role on environmental remediation and alternate energy production

Researchers debate on if it is only the crystalline properties of TiO2 or also the surface morphology and even optical properties of different types of TiO2 are the instrumental parameters on photocatalysis. It is a subject of exploration whether the phase pure anatase TiO2 or the heterojunctions and band alignment in the two polymorphs of TiO2(anatase and rutile) plays the determining role in efficacy of a photocatalytic reaction. Three different synthetic routes such as polymerizable sol–gel, solution combustion and customized microwave assisted hydrothermal method have been employed to synthesize TiO2. The materials are characterized systematically using XRD, FE-SEM, HR-TEM, diffuse reflectance, photoluminescence, BET surface area and Raman spectroscopy. It is found that TiO2 synthesized by polymerizable sol–gel approach yields a mixed phase of anatase and rutile, while the other two approaches yield phase pure anatase. The band gap obtained from diffuse reflectance measurements are compared with the direct and indirect band gaps derived from Kubelka–Munk plots. Among the three synthetic routes, TiO2 synthesized by customized microwave assisted hydrothermal method exhibits the highest surface area, pore volume and diameter, and lowest recombination, which in turn play a crucial role in high rate of photocatalytic degradation of methylene blue. On the other hand, the phase pure anatase made out of solution combustion route with moderate surface area, pore volume and diameter outperformed the rest two catalysts in photocatalytic hydrogen production. The different reaction specific photocatalytic efficacies of these two materials are discussed with respect to the combinatorial role of nano-crystallinity, surface properties, and optical properties.

Optical properties of honeycomb photonic structures

We study, theoretically and experimentally, optical properties of different types of honeycomb photonic structures, known also as `photonic graphene'. First, we employ the two-photon polymerization method to fabricate the honeycomb structures. In experiment, we observe a strong diffraction from a finite number of elements, thus providing a unique tool to define the exact number of scattering elements in the structure by a naked eye. Then, we study theoretically the transmission spectra of both honeycomb single layer and 2D structures of parallel dielectric circular rods. When the dielectric constant of the rod materials $\varepsilon$ is increasing, we reveal that a two-dimensional photonic graphene structure transforms into a metamaterial when the lowest TE${}_{01}$ Mie gap opens up below the lowest Bragg bandgap. We also observe two Dirac points in the band structure of 2D photonic graphene at the $K$ point of the Brillouin zone and demonstrate a manifestation of the Dirac lensing for the TM polarization. The performance of the Dirac lens is that the 2D photonic graphene layer converts a wave from point source into a beam with flat phase surfaces at the Dirac frequency for the TM polarization.

Do surface treatments affect the optical properties of ceramic veneers?

Surface treatments may affect the optical properties of ceramic veneers before cementation. The purpose of this study was to evaluate whether various surface treatments affect the optical properties of different types of ceramic veneers. Disk-shaped ceramic veneers (N=280) were prepared from the IPS e.max Press, e.max CAD, Empress Esthetic, e.max Ceram, and Inline ceramic systems with 0.5-mm and 1.0-mm thicknesses. The ceramics were divided into 4 groups: no surface treatments; etched with hydrofluoric acid; airborne-particle abraded with 30-μm Al2O3; and irradiated with erbium:yttrium-aluminum-garnet laser. A translucent shade of resin was chosen for cementation. Color parameters were examined with a colorimeter. Statistical analyses were done with 3-way ANOVA and the Bonferroni test (P=.05). Significant interactions were noted between the surface treatments, ceramic type, and thickness for ΔE values (P=.01), and no significant interactions were noted for L* (P=.773), a* (P=.984), and b* (P=.998). The greatest color change occurred after airborne-particle abrasion with 0.5-mm-thick e.max Press (2.9 ΔE). Significant differences in ΔE values were found among the hydrofluoric acid, airborne-particle abrasion, and laser groups for 0.5-mm-thick ceramics, except IPS Inline, and among the hydrofluoric acid, airborne-particle abrasion, and laser groups for 1.0-mm-thick ceramics, except Empress Esthetic ceramics. The color change of the ceramics increased after the surface treatments, particularly as the ceramics became thinner.

Complex Refractive Indices of Thin Films of Secondary Organic Materials by Spectroscopic Ellipsometry from 220 to 1200 nm

The complex refractive indices of three different types of secondary organic material (SOM) were obtained for 220 to 1200 nm using a variable angle spectroscopic ellipsometer. Aerosol particles were produced in a flow tube reactor by ozonolysis of volatile organic compounds, including the monoterpenes α-pinene and limonene and the aromatic catechol (benzene-1,2-diol). Optically reflective thin films of SOM were grown by electrostatic precipitation of the aerosol particles onto silicon substrates. The ellipsometry analysis showed that both the real and imaginary components of the refractive indices decreased with increasing wavelength. The real part n(λ) could be parametrized by the three-term form of Cauchy's equation, as follows: n(λ) = B + C/λ(2) + D/λ(4) where λ is the wavelength and B, C, and D are fitting parameters. The real refractive indices of the three SOMs ranged from 1.53 to 1.58, 1.49-1.52, and 1.48-1.50 at 310, 550, and 1000 nm, respectively. The catechol-derived SOM absorbed light in the ultraviolet (UV) range. By comparison, the UV absorption of the monoterpene-derived SOMs was negligible. On the basis of the measured refractive indices, optical properties were modeled for a typical atmospheric particle population. The results suggest that the wavelength dependence of the refractive indices can vary the Angstrom exponent by up to 0.1 across the range 310 to 550 nm. The modeled single-scattering albedo can likewise vary from 0.97 to 0.85 at 310 nm (UV-B). Variability in the optical properties of different types of SOMs can imply important differences in the relative effects of atmospheric particles on tropospheric photochemistry, as well as possible inaccuracies in some satellite-retrieved properties such as optical depth and mode diameter.

CLASSIFYING OPTICAL PROPERTIES OF SURFACE- AND BULK-SCATTERING BIOLOGICAL LAYERS WITH POLARIZATION SINGULAR STATES

The results of singular approach usage in the tasks of description and classification of appearance of optical anisotropy of different types of phase-inhomogeneous biological layers (surface-scattering, optically thin and optically thick) have been presented. The characteristic values of the fourth Stokes vector parameter (S4= 0 — linear polarization — (L-state); S4= ±1 — circular polarization — (±C-state)) have been chosen as the main analytical tool describing polarization-singular states. The value of S4has been determined by the value of phase shift between the orthogonal components of amplitude in the point of biological layer laser image and therefore is azimuthally stable. Hence, statistic moments of the first to the fourth orders characterizing the distribution of the amount of characteristic values S4= 0; S4= ±1 have been used for definition and differentiation of optical properties of different types of biological layers — surface scattering, optically thin and optically thick human skin.

Investigation of the optical properties of organic‐inorganic hybrid polymers by IR to Vis‐fUV spectroscopic ellipsometry

AbstractInorganic‐organic hybrid polymers are used as barrier coatings in order to protect flexible electronic devices from the permeation of atmospheric oxygen and water vapour that induce oxidation to the Flexible Electronic Device (FED) organic layers, reducing their operation, efficiency and stability. In this work, Spectroscopic Ellipsometry (SE) in a wide spectral region, from the infrared (IR) (900–4000 cm–1) to the Vis‐far UV (1.5‐6.5 eV) has been implemented in order to investigate the optical properties of different types of hybrid polymers, which are synthesized via the sol–gel technique onto Polyethylene Terephthalate (PET), SiOx/PET and AlOx/PET substrates. The analysis of the measured SE spectra revealed valuable information about the electronic and vibrational response as well as the cross‐linking mechanisms that control the interface and barrier properties of these materials. Finally, the correlation of the optical properties with the synthesis parameters and the barrier response of these materials will significantly contribute towards their optimization in order to be used as high barrier coatings. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Optical studies of carbon nanotubes and nanographites

Resonance Raman and photoluminescence excitation (PLE) spectroscopies are used to study the optical properties of different types of carbon nanostructures such as carbon nanotube, nanoribbons, nanographites and graphite edges. In the resonance Raman experiments of carbon nanotubes, the ( n , m ) assignment is obtained by comparing the experimental and theoretical diameter and chirality dependence of the optical transitions. The influence of the environment on the optical transitions of the nanotubes is also obtained in the Raman experiments. The PLE measurements in different samples of carbon nanotubes show both direct and phonon-assisted optical transitions, and the results give new evidences that the optical transitions in nanotubes have an excitonic character, which is very strong for the low energy transitions. We also analyze the Raman spectra of nanoribbons and nanographites, showing that this technique is an important tool for defect characterization in graphitic materials, and can be used to distinguish the atomic structure of the graphite edges.

Spectral Signatures of Surface Materials in Pig Buildings

Manual cleaning of pig production buildings based on high-pressure water cleaners is unappealing to workers, because it is tedious and health threatening. To replace manual cleaning, a few cleaning robots have been commercialised. With no cleanliness sensor available, the operation of these robots is to follow a cleaning procedure initially defined by the operator. Experience shows that the performance of such robots is poor regarding effectiveness of cleaning and utilisation of water. The development of an intelligent cleanliness sensor for robotic cleaning is thus crucial in order to optimise the cleaning process and to minimise the amount of water and electricity consumed. This research is aimed at utilising a spectral imaging method for cleanliness detection. Consequently, information on the reflectance of building materials and contamination in different spectral ranges is important. In this study, the optical properties of different types of surfaces to be cleaned and the dirt found in finishing pig units were investigated in the visual and the near infrared (VIS–NIR) optical range. Four types of commonly used materials in pig buildings, i.e. concrete, plastic, wood and steel were applied in the investigation. Reflectance data were sampled under controlled lighting conditions using a spectrometer communicating with a portable computer. The measurements were performed in a laboratory with materials used in a pig house for 4–5 weeks. The spectral data were collected for the surfaces before, during and after high-pressure water cleaning. The spectral signatures of the surface materials and dirt attached to the surfaces showed that it is possible to make discrimination and hence to classify areas that are visually clean. When spectral bands 450, 600, 700 and 800 nm are chosen, there are at least two spectral bands for each type of the materials, in which the spectral signals can be used for discrimination of dirty and clean condition of the surfaces.

Optimization of the fluorescence in situ hybridization (FISH) technique for high detection efficiency of very small proportions of target interphase nuclei.

Using commercially available fluorochrome-labeled probes specific for chromosomes X, Y, 13, 18, and 21, we optimized the technical protocols for fluorescence in situ hybridization (FISH) so that the highest sensitivity and specificity were achieved. Also, we compared the optical properties of different types of fluorescent labels in an effort to develop the most efficient FISH protocol, including the determination of which types of labels are the easiest to count accurately. The lymphocytes were purified from blood of normal male and female newborns, normal male and female adults, and a trisomy 21 male adult. Male and female lymphocytes were mixed in five different combinations. For each combination, the male lymphocytes either from newborns or from adults were diluted with female lymphocytes in seven different proportions. For each of these 35 different cell mixtures, 100,000 nuclei were analyzed and scored in a blind fashion. Among the different fluorochrome-labeled probes, the highest sensitivity and specificity were achieved when SpectrumAqua CEP-Y/SpectrumOrange CEP X probe mixture, SpectrumAqua CEP-18, SpectrumOrange LSI-13, and SpectrumOrange LSI-21 were hybridized. The hybridization sensitivity and specificity were higher than 99% for the identification of chromosomes X, Y, 13, and 18, and higher than 98% for the detection of trisomy 21. The proportion of false-positive signals was under 0.005% for XY detection and lower than 0.14% for autosome detection. With these high hybridization sensitivities and specificities, the optimized FISH protocol developed in our laboratory has the potential to detect very rare events, e.g., when the proportion of cells being sought is lower than 0.01%. In other words, our protocol allows the specific detection of one male cell sunken among 10,000 female cells.