Changes In Optical Thickness Research Articles

The use of a vascular endothelial growth factor inhibitor (ranibizumab) in macular edema due to eales disease.

To report the results of intravitreal use of ranibizumab in a patient with macular edema due to Eales disease. This was an open-label, Phase 1, 6-month study of the safety and efficacy of intravitreally administered ranibizumab in patients with macular edema due to Eales disease. A single patient was eligible for the study during the 2 years of recruitment. She received 3 monthly intravitreal injections of 0.5 mg of ranibizumab for 3 months. At each of her monthly visits during the 6-month study, she was evaluated with a full ocular examination and optical coherence tomography imaging of the macula. Primary outcome measure was change in optical coherence tomography central subfield thickness at 6 months. The central macular thickness as measured on optical coherence tomography reduced from 269 μm at baseline to 186 μm at 3 months. This reduction was transient with subsequent increase to 262 μm at the conclusion of the study at 6 months. Ranibizumab use led to transient resolution of macular edema at 3 months; however, this reduction in edema was not sustained.

Imaging the cellular response to transient shear stress using stroboscopic digital holography

We use stroboscopic quantitative phase microscopy to study cell deformation and the response to cavitation bubbles and transient shear stress resulting from laser-induced breakdown of an optically trapped nanoparticle. A bi-directional transient displacement of cytoplasm is observed during expansion and collapse of the cavitation bubble. In some cases, cell deformation is only observable at the microsecond time scale without any permanent change in cell shape or optical thickness. On a time scale of seconds, the cellular response to shear stress and cytoplasm deformation typically leads to retraction of the cellular edge most exposed to the flow, rounding of the cell body and, in some cases, loss of cellular dry mass. These results give a new insight into the cellular response to cavitation induced shear stress and related plasma membrane permeabilization. This study also demonstrates that laser-induced breakdown of a nanoparticle offers localized cavitation, which interacts with a single cell but without causing cell lysis.

Interferometric porous silicon transducers using an enzymatically amplified optical signal

This paper describes a novel transducer principle converting biomolecular binding events into changes in porous silicon structural colour. An enzyme-catalysed reaction, horseradish peroxidase (HRP) mediated oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB), induced an amplified optical detection signal on an antibody-functionalised porous silicon film, which manifested as significant changes in the Fabry–Pérot fringe pattern. Exposing porous silicon to non-oxidised TMB and oxidised TMB products and measuring the resulting effective optical thickness (EOT) changes of the porous silicon layer, an amplified signal from porous silicon was found, caused by an intermediate radical cation produced during the enzymatic-catalysed oxidation of TMB. Finally, it was shown that this system could be used to detect a human immunoglobulin (IgG) at 0.2 μg/ml. This work may lead to the development of new biosensors where porous silicon acts as the sensing matrix and transducer element.

Effects of implementing satellite observed aerosols into a mesoscale atmosphere model

This study investigated the performance of the fifth-generation Pennsylvania State University–National Center for Atmospheric Research (PSU-NCAR) Mesoscale Model (MM5) in calculating the aerosol forcing on cloud cover, incoming surface solar radiation, and near-surface air temperature via the implementation of aerosol optical depth in the shortwave radiation parameterization. MM5 simulations with and without aerosol data are performed in the periods of 6–7 August 2003 and 19–21 September 2003 during which strong aerosol forcing was observed with Moderate Resolution Imaging Spectroradiometer (MODIS) data in the mid-Atlantic region. Both periods clearly showed that aerosols had a direct negative effect on surface solar radiation through aerosol scattering. For example, every 0.1 change in MODIS aerosol optical thickness (AOT) results in 44 and 59 W m−2 decreases in surface solar radiation for the first and second periods, respectively. A magnitude of 0.1 increment in MODIS AOT reduces air temperature 0.36 and 0.56 K for the first and second periods, respectively. Comparisons with satellite-derived surface solar radiation retrievals showed that aerosol implementation in MM5 consistently showed better incoming surface solar radiation than that of the non-aerosol case. This helps to reduce uncertainties related to the radiation–cloud–aerosol interaction in numerical weather modelling systems.

Optical characteristics of pulsed laser deposited Ge–Sb–Te thin films studied by spectroscopic ellipsometry

Pulsed laser deposition technique was used for the fabrication of (GeTe)1−x(Sb2Te3)x (x = 0, 0.33, 0.50, 0.66, and 1) amorphous thin films. Scanning electron microscopy with energy-dispersive x-ray analysis, x-ray diffraction, optical reflectivity, and sheet resistance temperature dependences as well as variable angle spectroscopic ellipsometry measurements were used to characterize as-deposited (amorphous) and annealed (rocksaltlike) layers. In order to extract optical functions of the films, the Cody–Lorentz model was applied for the analysis of ellipsometric data. Fitted sets of Cody–Lorentz model parameters are discussed in relation with chemical composition and the structure of the layers. The GeTe component content was found to be responsible for the huge optical functions and thickness changes upon amorphous-to-fcc phase transition.

Decadal changes in aerosol optical thickness and single scattering albedo estimated from ground-based broadband radiometers: A case study in Japan

[1] A method to estimate aerosol optical thickness and single scattering albedo from broadband direct and diffuse irradiances was developed. Using irradiances simulated with and without errors, the accuracies of estimated optical thickness from 0.7 to 0.8 μm and single scattering albedo in the visible wavelength region were determined to be about 0.02 and 0.05, respectively. Resulting time variations in optical thickness and single scattering albedo by broadband radiometers agreed well with sky radiometer retrievals. Long-term variations in optical thickness and single scattering albedo from 1975 to 2008 at Tsukuba, Japan, were estimated by the method described. Optical thickness increased until the mid-1980s, then decreased until the late 1990s, and was almost constant in the 2000s. The single scattering albedo was about 0.8 until the late 1980s, gradually increased, and has remained at approximately 0.9 since the mid-1990s. The surface global irradiance under clear sky conditions calculated from estimated aerosol optical properties showed an apparent transition from dimming to brightening around the mid-1980s. The magnitude of the brightening was about 12.7 W m−2; of this, 8.3 W m−2 was due to a decrease in optical thickness, and the remaining 4.4 W m−2 was due to an increase of single scattering albedo. On the other hand, the surface global irradiance measured under cloudy conditions increased by 2.6 W m−2. The dimming and brightening by aerosols were weakened by the changes in clouds. The method described could be useful in evaluating aerosol influences on long-term changes in the surface solar radiation at many sites around the world.

Chemical resistance of porous silicon: photolithographic applications

AbstractLow‐temperature passivation is employed in this study to improve the chemical resistance of porous silicon to both weak‐alkali and HF solutions, enabling complex and multi‐mask patterning of porous silicon. Passivation is achieved by annealing the film in N2 atmosphere at temperatures ranging from 560°C‐800°C. The resistance of the passivated porous silicon to both KOH and HF solutions was examined by immersing the sample into these solutions and working out the optical thickness change. It is shown that higher passivation temperatures result in improved chemical resistance. Infrared spectroscopy show that exposing the films to HF can remove the passivation layer, enabling repeated anodisation; the restoration of the hydrogen bond on the porous silicon surface after HF immersion makes repeated passivation and processing possible (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Photo-induced optical changes in GexAs40Se60–xthin films

AbstractGe-As-Se chalcogenide thin films show a wide range of photosensitivity, which is utilized for the fabrication of micro-optical elements for integrated optics. The photosensitivity of GexAs40Se60–x(x=0, 15) chalcogenide thin films for UV light was presented. For that purpose, the bulk samples of GexAs40Se60–x(x=0, 15) chalcogenide glasses were prepared using conventional melt quenching technique, and thin films were prepared using thermal evaporation technique. These thin films were exposed to UV light for two hours. Amorphous natures of bulk samples and thin films were verified by XRD and chemical compositions were verified by EDX measurements. The thicknesses of the thin films were measured using a thickness profilometer. Linear optical analysis of these thin films was done using transmission spectra in wavelength range of 300–900 nm. Optical bandgap was determined by first peak of transmission derivative as well as extrapolation of Tauc's plot. R2 analysis was done using R software to ensure that the material is indirect bandgap material. It is observed that two hours UV exposure causes photo-darkening along with photo-expansion in As40Se60 thin films, while photo-bleaching and photo-densification for Ge15As40Se45 thin films. However, the amounts of photo-induced optical changes for Ge15As40Se45 thin films are smaller than those for As40Se60 thin films. The changes in optical absorption, bandgap and thickness are understood based on the bonding rearrangement caused by UV exposure.

Chemical Sensor Based on Porous Silicon Dual Transducers

Novel porous Si exhibiting dual optical properties, both Fabry-Perot fringe (optical reflectivity) and photoluminescence, were developed and used as chemical sensors. Porous Si samples were prepared by an electrochemical etch of p-type silicon under the illumination with a 300 W tungsten filament bulb for the duration of etch. The surface of porous Si was characterized by FT-IR instrument. The porosity of samples was about 80%. Both reflectivity and photoluminescence were simultaneously measured under the exposure of organic vapors. The shift of Fabry-Perot fringe to the longer wavelength under the exposure of chloroform vapors was obtained. The steady-state photoluminescence spectra and quenching photoluminescence under the exposure of various organic vapors were obtained. A set of organic compounds were analyzed by both quenching photoluminescence and change of optical thickness.

Multiangular Polarized Characteristics of Optically Thin Cirrus in the Visible and Near-Infrared Spectral Region

AbstractOptically thin cirrus play a key role in the earth’s radiation budget and global climate change. Their radiative effects depend critically on the thin cirrus optical and microphysical properties. In this paper, inhomogeneous hexagonal monocrystals (IHMs), which consist of a pure hexagon with spherical air bubble or aerosol inclusions, are applied to calculate the single-scattering properties of individual ice crystals. The multiangular polarized characteristics of optically thin cirrus for the 0.865- and 1.38-μm spectral bands are simulated on the basis of an adding–doubling radiative transfer program. The sensitivity of total and polarized reflectance at the top of the atmosphere (TOA) to different aerosol, cirrus, and surface parameters is studied. A new sensitivity index is introduced to further quantify the sensitivity study. The TOA polarized reflectance measured by the Polarization and Directionality of the Earth’s Reflectance (POLDER) instruments is compared to simulated TOA total and polarized reflectance. The test results are reasonable, although small deviations caused by the change of aerosol properties and thin cirrus optical thickness do exist. Finally, on the basis of the sensitivity study, a conceptual approach is suggested to simultaneously retrieve thin cirrus clouds’ optical thickness, ice particle shape, and the underlying aerosol optical thickness using the TOA total and polarized reflectance of the 0.865- and 1.38-μm spectral bands measured at multiple viewing angles.

FTRIFS biosensor based on double layer porous silicon as a LC detector for target molecule screening from complex samples

Post-column identification of target compounds in complex samples is one of the major tasks in drug screening and discovery. In this work, we demonstrated that double layer porous silicon (PSi) attached with affinity ligand could serve as a sensing element for post-column detection of target molecule by Fourier transformed reflectometric interference spectroscopy (FTRIFS), in which trypsin and its inhibitor were used as the model probe–target system. The double layer porous silicon was prepared by electrical etching with a current density of 500 mA/cm 2, followed by 167 mA/cm 2. Optical measurements indicated that trypsin could infiltrate into the outer porous layer (porosity 83.6%), but was excluded by the bottom layer (porosity 52%). The outer layer, attached with trypsin by standard amino-silane and glutaraldehyde chemistry, could specifically bind with the trypsin inhibitor, acting as a sample channel, while the bottom layer served as a reference signal channel. The binding event between the attached trypsin and trypsin inhibitor samples could be detected by FTRIFS in real-time through monitoring the optical thickness change of the porous silicon layer. The baseline drift caused by sample matrix variation could be effectively eliminated by a signal correction method. Optical signals had a linear relationship with the concentration of trypsin inhibitor in the range of 10–200 ng mL −1. The FTRIFS biosensor based on double layer porous silicon could be combined with a UV detector for screening the target molecule from complex component mixtures separated by a LC column. Using an LC–UV–FTRIFS system, a fraction containing a trypsin inhibitor could be separated from a soybean extract sample and identified in real-time.

Comprehensive formulation of temperature-dependent dispersion of optical materials: illustration with case of temperature tuning of a mid-IR HgGa_2S_4 OPO

The temperature dependence of refractive indices of optical materials is characterized in this work by what we call their normalized thermo-optic coefficients. These are determined experimentally through interferometric measurements of thermal expansion and of changes in optical thickness at a few laser wavelengths as function of temperature. A suitable vectorial formalism applied to these data allows predicting the thermal evolution of the refractive index all over the useful range of transparency. The validity and reliability of our methodology is demonstrated through temperature tuning of a mid-IR HgGa2S4 optical parametric oscillator (OPO) pumped at 1.0642 μm by a Nd:YAG laser. Measured thermal variation of both signal and idler wavelengths agrees very well with the predicted one.

Changes in Cloud Optical Thickness and Cloud Drop Size Associated with Precipitation Measured with TRMM Satellite

We derived rain rate, cloud optical thickness and the effective radius in water clouds by a combined use of the Precipitation Radar and the Visible and Infrared Scanner onboard the Tropical Rainfall Measuring Mission. The derived data were used to study how cloud optical thickness relates to precipitation. In particular, we focused on the changes in cloud optical thickness resulted from changes in the size distributions of cloud droplets associated with precipitation. There were considerable scatter between cloud optical thickness and rain rate on a global scale. However, cloud optical thickness was found to increase with rain rate on average. The tendency to increase was mostly due to increases in liquid water path and depended on rain rate. For strong rain, relatively small increases in the optical thickness with rain rate were observed. Whereas, for weak rain, larger increases with rain rate were found, which is related to considerable changes in liquid water path and in the effective radius of cloud droplets. To study the effects of drop size variation, the relationships between cloud optical thickness and rain rate for same values of liquid water path were analyzed. Results show that there were no significant dependences of cloud optical thickness on rain rate for strong rain. For weak rain, cloud optical thickness was found to decrease with rain rate. In particular, significant differences of optical thickness were found between non-precipitating clouds and precipitating clouds: smaller cloud optical thickness was observed for precipitating clouds. Dispersion of cloud drop size was found in the rain formation process, which may relate to changes in the shape of drop size spectra and leads to the decreases in the cloud optical thickness for precipitating clouds.

Ultrafast spectroscopy of optical microcavity modes on the unique femtosecond spectrometric complex at the institute of spectroscopy RAS

The relaxation of nonequilibrium charge carriers in ZnSe films on metal substrates has been investigated by the femtosecond spectroscopic pump-supercontinuum probe method. Upon subgap and overgap excitations of ZnSe, red and blue photoinduced frequency shifts for the interference cavity modes in ZnSe films on chromium have been revealed. Such shifts and features of the relaxation times are explained by photoinduced changes in the boundary conditions and optical thickness of the microcavity.

Label-free optical detection of peptide synthesis on a porous silicon scaffold/sensor.

Mesoporous porous silicon (PSi) microcavity sensors are used to conduct conventional solid-phase peptide synthesis. The sensor optical response provides a convenient means to monitor the synthesis reaction in a nondestructive manner. Measurements indicate that peptide synthesis occurs only when the PSi sensor/scaffold is amine-terminated using, for example, the amino silane or deprotected acid-labile Rink linker. Equivalent coupling efficiencies of the first amino acid to both amine terminations are observed. Kinetic studies indicate that coupling reactions are 90% complete in 1 h. Quantitative analysis of the optical response following the synthesis of homo-oligopeptides (4-mers) suggests that coupling efficiencies and/or optical thickness changes depend on the peptide length. The synthesis of the cell adhesive oligopeptide (RGD) was monitored by the optical sensor response and validated by the cell culture of primary dermal fibroblasts. Secondary ion mass spectrometry (SIMS) analysis successfully detected peptide on the silicon wafer adjacent to the PSi. Our findings suggest the potential to exploit the high surface area, efficient coupling, and intrinsic optical detection properties of PSi for label-free high-throughput screening.

Global model simulations of the impact of ocean-going ships on aerosols, clouds, and the radiation budget

Abstract. International shipping contributes significantly to the fuel consumption of all transport related activities. Specific emissions of pollutants such as sulfur dioxide (SO2) per kg of fuel emitted are higher than for road transport or aviation. Besides gaseous pollutants, ships also emit various types of particulate matter. The aerosol impacts the Earth's radiation budget directly by scattering and absorbing the solar and thermal radiation and indirectly by changing cloud properties. Here we use ECHAM5/MESSy1-MADE, a global climate model with detailed aerosol and cloud microphysics to study the climate impacts of international shipping. The simulations show that emissions from ships significantly increase the cloud droplet number concentration of low marine water clouds by up to 5% to 30% depending on the ship emission inventory and the geographic region. Whereas the cloud liquid water content remains nearly unchanged in these simulations, effective radii of cloud droplets decrease, leading to cloud optical thickness increase of up to 5–10%. The sensitivity of the results is estimated by using three different emission inventories for present-day conditions. The sensitivity analysis reveals that shipping contributes to 2.3% to 3.6% of the total sulfate burden and 0.4% to 1.4% to the total black carbon burden in the year 2000 on the global mean. In addition to changes in aerosol chemical composition, shipping increases the aerosol number concentration, e.g. up to 25% in the size range of the accumulation mode (typically >0.1 μm) over the Atlantic. The total aerosol optical thickness over the Indian Ocean, the Gulf of Mexico and the Northeastern Pacific increases by up to 8–10% depending on the emission inventory. Changes in aerosol optical thickness caused by shipping induced modification of aerosol particle number concentration and chemical composition lead to a change in the shortwave radiation budget at the top of the atmosphere (ToA) under clear-sky condition of about −0.014 W/m² to −0.038 W/m² for a global annual average. The corresponding all-sky direct aerosol forcing ranges between −0.011 W/m² and −0.013 W/m². The indirect aerosol effect of ships on climate is found to be far larger than previously estimated. An indirect radiative effect of −0.19 W/m² to −0.60 W/m² (a change in the atmospheric shortwave radiative flux at ToA) is calculated here, contributing 17% to 39% of the total indirect effect of anthropogenic aerosols. This contribution is high because ship emissions are released in regions with frequent low marine clouds in an otherwise clean environment. In addition, the potential impact of particulate matter on the radiation budget is larger over the dark ocean surface than over polluted regions over land.

Nanoporous Zeolite Thin Film-Based Fiber Intrinsic Fabry-Perot Interferometric Sensor for Detection of Dissolved Organics in Water

A fiber optic intrinsic Fabry-Perot interferometric (IFPI) chemical sensor wasdeveloped by fine-polishing a thin layer of polycrystalline nanoporous MFI zeolitesynthesized on the cleaved endface of a single mode fiber. The sensor operated bymonitoring the optical thickness changes of the zeolite thin film caused by the adsorption oforganic molecules into the zeolite channels. The optical thickness of the zeolite thin filmwas measured by white light interferometry. Using methanol, 2-propanol, and toluene as themodel chemicals, it was demonstrated that the zeolite IPFI sensor could detect dissolvedorganics in water with high sensitivity.

Extreme Ultraviolet Emission from Laser-Irradiated Low-Density Xe Targets

The effect of the initial density of xenon (Xe) targets on extreme ultraviolet (EUV) emission has been investigated. With decreasing initial density, it was found that the spectral width around 11 nm becomes broad, and the intensity of 13.5 nm emission increases. The maximum conversion efficiency (CE) for solid Xe targets is approximately 0.6% at a 2×1011 W/cm2 of laser intensity, whereas that for the low-density targets is approximately 0.7% at a 4×1011 W/cm2. The spectral broadening with decreasing initial density can be attributed to the change in optical thickness of laser-produced plasmas. The enhancement of CE is attributed to optically thick plasma formation.

Fabrication of High-Mobility Nitrided Hafnium Silicate Gate Dielectrics with Sub-1-nm Equivalent Oxide Thickness Using Plasma Nitridation and High-Temperature Postnitridation Annealing

Changes in optical thickness and equivalent oxide thickness (EOT) during postdeposition annealing (PDA) and postnitridation annealing (PNA) were investigated to fabricate sub-1-nm-EOT nitrided hafnium silicate (HfSiON) gate dielectrics. In spite of optical thickness reductions by PDA, none of the PDA conditions could reduce the EOT and bring about the merit in leakage current reduction. On the other hand, high-temperature PNA without oxygen was found to be effective for reducing both optical thickness and EOT. Furthermore, leakage current reduction ratio and effective mobility were improved by applying high-temperature PNA. Consequently, the fabrication of 0.81-nm-EOT HfSiON gate dielectrics with a gate leakage current of 0.74 A/cm2 at 0.7 V and an electron mobility of 235 cm2/(V s) at 0.8 MV/cm (76% of SiO2) has been realized.

Label-free characterisation of oligonucleotide hybridisation using reflectometric interference spectroscopy

The potential of a label-free detection method, reflectometric interference spectroscopy (RIfS), for temperature-dependent DNA hybridisation experiments (for example in single nucleotide polymorphism (SNP) analysis) is investigated. Hybridisations of DNA, peptide nucleic acid (PNA), and locked nucleic acid (LNA) to a single stranded DNA were measured for several temperatures, and the melting curves and temperatures were calculated from the changes in optical thickness obtained. These measurements were performed by hybridising surface-immobilised single stranded oligomers with their complementary ssDNA or with ssDNA containing SNPs at different temperatures. DNA was compared to its analogue oligomers PNA and LNA due to their stability against nuclease. A comparison of melting temperatures demonstrated the higher binding affinities of the DNA analogues. Moreover, a continuous melting curve was obtained by first hybridising the functionalised surface with its complementary DNA at room temperature and then heating up in-flow. Measurement of the continuous melting curve was only possible due to the insensitivity of the RIfS method towards temperature changes. This is an advantage over other label-free detection methods, which are based on determining the refractive index.