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At least 1,315 records · Page 73Linked to original sources
PubMed2007

Plasmon resonances in gold-coated tilted fiber Bragg gratings.

The transmission spectrum of fiber Bragg gratings with gratings planes tilted at a small angle (2 degrees -10 degrees) relative to the fiber axis shows a large number of narrowband cladding mode resonances within a 100 nm wide spectrum. When a gold coating with a thickness between 10 and 30 nm is deposited on the fiber, the transmission spectrum shows anomalous features for values of the outside medium refractive index between 1.4211 and 1.4499. These features are shown to correspond to the excitation of surface plasmon resonances at the external surface of the gold film.

Fiber Optic Technology↗
PubMed2003

Simulation on wavelength-dependent complex refractive index of liquids obtained by phase retrieval from reflectance dip due to surface plasmon resonance.

A method for the calculation of the wavelength-dependent complex refractive index of absorbing liquid from reflectance in the vicinity of surface plasmon resonance (SPR) is presented. The calculation is based on the maximum entropy method (MEM). As an example, phase retrieval from a simulated SPR reflectance of a red colored liquid solution is carried out. It is proposed that MEM can be applied to wavelength-dependent complex refractive index assessment from reflectance of absorbing liquids in SPR measurement in wavelength scanning mode.

Algorithms↗
PubMed2003

Reflectometric study of contaminant layer on a probe window.

In this study properties of a contaminant material on the surface of a probe window (prism) were investigated. The probe window, i.e., the prism, is part of the reflectometer apparatus exploited in this study. The contaminant layer was considered to originate from a pulping solution containing lignin contacting the surface of the prism. In these experiments the contact time was up to 5.0 hours. To find the values of the contaminant material properties, i.e., refractive index (n), extinction coefficient (k), and effective thickness (d), an optical model was proposed assuming that the contaminant layer is continuous and homogenous. In addition, the model includes an inter-diffusion layer existing between the contaminant layer and the lignin solution. From the fitting procedure using the optical model of depth profiling, it was found that the growth rate of the contaminant layer was approximately 60 nm per hour. The results obtained by theory and experiments were consistent for both s- and p-polarizations and for the various wavelengths of the light source (300, 400, and 500 nm).

Artifacts↗
PubMed2003

Confocal Raman microspectrometry: a vectorial electromagnetic treatment of the light focused and collected through a planar interface and its application to the study of a thin coating.

In-depth confocal Raman microspectrometry (CRM) studies through a planar interface between materials of mismatched refraction indices are known to be affected by a decrease of both the collected Raman intensity and the axial resolution as a function of the penetration depth. Following a previous model, which takes the refraction, diffraction, and spherical aberration effects into account when focusing a Gaussian incident laser beam with a high numerical aperture objective lens, a complete vectorial treatment of these phenomena is considered. It is demonstrated that off-axis refraction effects cannot be neglected and that the dimension of the confocal pinhole aperture plays a crucial role on the effective focal plane position and on the collection efficiency. We thus propose a more rigorous and complete approach to the problem, and we find a very good agreement between experimental and theoretical Raman intensity variations for a thick polyethylene sample as a function of the penetration depth. As compared with calculations where only refraction was considered, we confirm that the lengthening of the focus even for a large penetration depth is significantly reduced upon diffraction effects. As an illustrative example, the theoretical Raman responses for a thin coating of approximately 20 microns on a polymer substrate were investigated and compared to experimental results already published. Even though the interfacial region is spread over approximately 5-6 microns when using a 100x objective and a confocal pinhole of 200 microns diameter, it is definitively concluded that the apparent axial resolution is not drastically deteriorated with increasing depth and that the coating thickness may be directly estimated with a precision of approximately 1.0 micron (5%).

Algorithms↗
PubMed2003

Differential thermal lensing in extended samples.

We present a new scheme for a pump-probe mode-mismatched thermal lensing experiment aimed at extracting the value of low-absorbing components in the presence of a high-absorbing background. The method allows for the use of large path-length samples. Changes in the background absorption of a column of ethanol of 20 cm of 1% and a pollutant concentration detection limit of 0.04 ppm are obtained when using a pump light power of 34 mW.

Differential Thermal Analysis↗
PubMed2004

Simple fiber-optic-based sensors for process monitoring: an application in wine quality control monitoring.

The goal of this research was to develop a simple and economical fiber-optic sensor technology for agrifood process monitoring. Toward this end, two fiber-optic sensors were developed to be used in combination: a single reflection V-bend sensor and a single fiber air-gap probe. The former is designed to be sensitive toward refractive index and the latter towards absorption. Experiments indicate that the micromachined V-bend fiber refractometer is most sensitive when the bend angle is centered around 140 degrees, at which angle the sensor may resolve changes in refractive index as small as 0.00015. Additionally, the V-bend sensor was found to be non-responsive toward sample absorption even in extremely absorbing solutions. The air-gap design absorption sensor, most commonly used for measurements in highly colored media, was found to be slightly sensitive towards refractive index. When the two sensors are used together, the response of the absorption sensor may be corrected for. This sensor combination is able to provide accurate measurements in situations where Beer's law is not obeyed. Results are presented that show that the sensor pair was successfully used to monitor wine sugar content (Brix), and color density and hue, parameters related to the age of the wine.

Absorption↗
PubMed2004

Fourier transform near-infrared spectrometer using a corner-cube integrated prism scanning interferometer.

This paper describes a Fourier transform (FT) near-infrared spectrometer that uses an integrated prism scanning interferometer whose optical paths are stabilized by corner cubes. A combination of corner cubes and a retroreflection mirror, which is sometimes used in the conventional interferometer for FT spectrometers, is adopted and adapted to the integrated prism scanning interferometer through a special design. Without any degradation of spectroscopic properties, the optical path in the interferometer is highly stabilized and the moving distance of the stage is halved. These advantages provide a robust and portable FT spectrometer for field use.

Equipment Design↗
PubMed2004

Surface plasmon spectral fingerprinting of adsorbed magnesium phthalocyanine by angle and wavelength modulation.

A novel instrumental method for angle and wavelength modulated surface plasmon resonance (SPR) spectroscopy is applied to the problem of spectral selectivity in SPR experiments. For transparent analytes, SPR reflectivity data are reduced to a two-dimensional (2D) spectrum of resonance wavelength versus incident angle, lambdaSPR(theta). This spectrum encodes the refractive index (RI) dispersion of the analyte and illustrates the increased SPR spectral shift per unit RI change at longer wavelengths (lower angle). For the absorbing analyte magnesium phthalocyanine (MgPc), the 2D data reduction method is complicated by the way the SPR and MgPc-based spectral peaks mix. Fresnel reflectivity models support experimental observations of spectral branching and qualitative fingerprints in the form of branched spectra, and difference reflectivity deltaR(lambda, theta) contour plots are presented.

Adsorption↗
PubMed2005

Development of a universal ellipsoidal mirror device for fluorescence detected circular dichroism: elimination of polarization artifacts.

We have developed an ellipsoidal mirror fluorescence detected circular dichroism (FDCD) device with enhanced detection sensitivity that eliminates the polarization artifact; this is applicable to samples with strongly polarized fluorescence. The device, JASCO FDCD465, has an ellipsoidal mirror structure with a framework consisting of three mirrors (one elliptical and two plane mirrors) that maximally collects light in the FDCD. All assemblies on the device including the ellipsoidal mirror, cylindrical cell, and photomultiplier tube (PMT) are aligned on the chamber-fitting sample mount as an attachment compatible with a standard CD spectropolarimeter. The new FDCD465 device eliminates the polarization artifact caused by anisotropic distribution of the emitted light. It represents a convenient, reliable, and sensitive FDCD attachment to the JASCO J-800 CD spectrometer series that can be used under both isotropic and photoselected conditions.

Artifacts↗
PubMed2005

Optical characterization of varnish films by spectroscopic ellipsometry for application in artwork conservation.

The specific aim of this paper is to measure the optical constants of fresh varnish layers up to a thickness of 10 mum by spectroscopic ellipsometry. It is the first time that this technique has been used in artwork conservation and it may prove very promising due to its nondestructive character. Samples of fresh dammar varnish (natural resin) and Paraloid B72 (synthetic resin) applied on glass and carbon black acrylic paint were analyzed. Both varnishes were considered as perfect dielectrics, and the real part of their refractive index was described by the Cauchy model: n (lambda) = A + B/lambda(2) + C/lambda(4). The Cauchy coefficients for dammar varnish and Paraloid B72 were then determined for layers of known thickness. The ellipsometric data were fitted to a model, which includes a mixed varnish-air layer. The optical properties of this layer were calculated by the Bruggeman effective medium approximation. In the case of carbon black acrylic paint, another mixed layer (paint-varnish) was added to the model. The results are very close to the values given in the literature. Given the measurement reproducibility, the results show that ellipsometry can discriminate between dammar varnish and Paraloid B72. This is very important in artwork conservation studies, because it has been done by time-consuming, destructive techniques up to now. Future work includes measurements of other types of natural and synthetic varnishes, in an attempt to introduce a nondestructive method for picture varnish identification and aging studies.

Algorithms↗
PubMed2005

New developments in planar array infrared spectroscopy.

A planar array infrared (PA-IR) spectrograph offers several advantages over other infrared approaches, including high acquisition rate and sensitivity. However, it suffers from some important drawbacks, such as a limited spectral range and a significant curvature of the recorded spectral images, which still need to be addressed. In this article, we present new developments in PA-IR spectroscopy that overcome these drawbacks. First, a data processing method for the correction of the curvature observed in the spectral images has been developed and refined. In addition, a dual-beam instrument that allows the simultaneous recording of two independent spectral images has been developed. These two improvements have been combined to demonstrate the real-time background correction capability of PA-IR instruments. Finally, the accessible spectral range of the PA-IR spectrograph has been extended to cover simultaneously the methylene stretching (3200-2800 cm(-1)) and the finger-print (2000-1000 cm(-1)) spectral regions.

Algorithms↗
PubMed2005

Depth profiling of the optical absorption coefficient in ultraviolet-degraded poly(vinylchloride) films by dual beam light profile microscopy.

Dual beam laser light profile microscopy (LPM) was applied in this work to the depth mapping of the optical absorption coefficient in photo-degraded poly(vinyl chloride) films. Depth profiles followed the absorption coefficient of a conjugated polyene photoproduct at visible wavelengths in photolyzed films of approximately 200 mum thickness. Both continuous and layered (separable laminate) films were studied. The absorption coefficient profiles reconstructed from photo-degraded thin films showed the classic concentration profiles seen in the literature for PVC degraded in the presence of oxygen and nitrogen atmospheres. In the case of single thin layers with continuous properties, the depth profiles were smooth and regular with minimum spatial noise. In the LPM of laminate structures, more optical anomalies were present because of the multiply interfacial structures that appeared in both the images and the reconstructed depth profiles. Notwithstanding, it was possible to profile the optical absorption coefficient at a level of error comparable to standard microtome methods. The latter was determined by comparing the LPM results to a destructive layer-by-layer analysis performed in parallel on the imaged materials. The dual beam LPM method should be generally useful for establishing polyene concentration profiles in industrial materials produced by photochemical, thermal, and chemical degradation mechanisms.

Absorption↗
PubMed2005

Nanoliter serum sample analysis by mid-infrared spectroscopy for minimally invasive blood-glucose monitoring.

The aim of this study was to demonstrate that mid-infrared spectroscopy is able to quantify glucose in a serum matrix with sample volumes well below 1 muL. For this, we applied mid-infrared attenuated total reflectance (ATR) or transmission-based spectroscopic methods to glucose quantification in microsamples of dry-film sera, either undiluted or diluted 10 times in distilled water. The sample series spanned physiological glucose concentrations between 50 and 600 mg/dL and volumes of 80, 8, and 1 nL. Calibration was carried out using multivariate partial least-squares (PLS) modeling with spectral data between 1180 and 940 cm(-1). Best performance was achieved in the ATR experiments. For raw ATR spectra, the optimum standard error of prediction (SEP) of 13.3 mg/dL was obtained for the 8 nL sample series with subsequent 10-fold dilution. With respect to the coefficient of variation of the glucose assay, CV(pred), we obtained a value of 3% for the 80 nL volume samples with spectral preprocessing using matrix protein absorption bands as an internal standard, 4% for the 8 nL samples, and 6% for the 1 nL samples with raw data. Spectral standardization resulted in significant improvement, especially for the 80 nL volume sample series. By contrast, the accuracy of the glucose assay for the 1 nL sample volume series could not be improved either by internal standardization or by considering the dry film areas for normalization, which we attribute to varying topographies of the dry films.

Blood Chemical Analysis↗
PubMed2005

Standard reference material 2036 near-infrared reflection wavelength standard.

Standard Reference Material 2036 (SRM 2036) is a certified transfer standard intended for the verification and calibration of the wavelength/wavenumber scale of near-infrared (NIR) spectrometers operating in diffuse or trans-reflectance mode. SRM 2036 Near-Infrared Wavelength/Wavenumber Reflection Standard is a combination of a rare earth oxide glass of a composition similar to that of SRM 2035 Near-Infrared Transmission Wavelength/Wavenumber Standard and SRM 2065 Ultraviolet-Visible-Near-Infrared Transmission Wavelength/Wavenumber Standard, but is in physical contact with a piece of sintered poly(tetrafluoroethylene) (PTFE). The combination of glass contacted with a nearly ideal diffusely reflecting backing provides reflection-absorption bands that range from 15% R to 40% R. SRM 2036 is certified for the 10% band fraction air wavelength centroid location, (10%)B, of seven bands spanning the spectral region from 975 nm to 1946 nm. It is also certified for the vacuum wavenumber (10%)B of the same seven bands in the spectral region from 10 300 cm(-1) to 5130 cm(-1) at 8 cm(-1) resolution. Informational values are provided for the locations of thirteen additional bands from 334 nm to 804 nm.

Fiber Optic Technology↗
PubMed2005

Mid-infrared fiber-optic attenuated total reflection spectroscopy of the solid-liquid phase transition of water.

Measurements of mid-infrared (MIR) absorption spectra of water and heavy water were carried out by fiber-optic evanescent wave spectroscopy, using silver halide (AgClBr) infrared fibers. Such measurements were performed for the first time on one sample, during the solid-liquid phase transition. From the variation of the spectra with temperature we found a new isosbestic point (at 3280 cm(-1) for H(2)O or at 2475 cm(-1) for D(2)O) and we identified five components of the O-H (O-D) stretch band. These phenomena have provided new information about the molecular structure of water.

Computer Simulation↗
PubMed2005

Monitoring the thermal gelation of cellulose ethers in situ using attenuated total reflectance fourier transform infrared spectroscopy.

In this work attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy was used to probe the thermal gelation behavior of aqueous solutions of hydroxypropyl methylcellulose (HPMC), specifically thermal gelation and accompanying precipitation. Cloud point measurements are usually evaluated through turbidity in dilute solutions but the method cannot readily be applied to more concentrated or highly viscous solutions. From the ATR-FTIR data, intensity changes of the nu(CO) band marked the onset of gelation and information about the temperature of gelation and the effect of the gel structure on the water hydrogen bonding network was elucidated. Changes in the relative intensities of bands associated with the methoxyl groups and hydrogen-bond-forming secondary alcohol groups indicated that hydrophobic polymer chain interactions were involved in the gelation process. The dominance of inter-molecular H bonding over intra-molecular H bonding within the cellulose ether in solution was also observed. The ATR-FTIR data was in good agreement with measurements of turbidity conducted on the same systems. The work indicates significant potential for the use of ATR-FTIR for the investigation of gelation and cloud point measurements in viscous cellulosic formulations.

Ether↗
PubMed2005

Using the intrinsic chirality of a molecule as a label-free probe to detect molecular adsorption to a surface by second harmonic generation.

Chiral second harmonic generation (C-SHG) has been used for the label-free detection of (R)-(+)-1,1'-bi-2-naphthol (RBN) and (S)-(+)-1,1'-bi-2-naphthol (SBN) binding to planar-supported lipid bilayers of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphotidylcholine (POPC) based on the intrinsic chirality of the molecules. C-SHG adsorption isotherms of RBN and SBN reveal Langmuir adsorption behavior with binding constants of 2.7 +/- 0.2 x 10(5) M(-1) and 3.0 +/- 0.1 x 10(5) M(-1), respectively. The kinetics of RBN binding to a POPC bilayer was also measured. It was determined that the adsorption rate for RBN was 5.7 +/- 0.4 x 10(3) s(-1)M(-1) and the desorption rate was 2.1 +/- 0.8 x 10(-2) s(-1). From the kinetic data a binding constant of 2.7 +/- 1.0 x 10(5) M(-1) was calculated, which agrees well with the thermodynamic measurement. The C-SHG technique was correlated with surface tension measurements in order to determine the RBN surface excess within the POPC membrane. The maximum surface excess of RBN in a monolayer of POPC was 4.3 +/- 0.5 x 10(-11) mol cm2. Using the maximum surface excess in conjunction with the C-SHG binding data a lower limit of detection of 1.5 +/- 0.1 x 10(-13) mols cm(-2) was calculated. The results of these studies show that C-SHG is a powerful tool for the study of chiral molecular interactions at surfaces.

Adsorption↗
PubMed2005

Infrared specular reflection spectroscopy of rough metallic substrates.

A study of the infrared reflectance of rough metallic surfaces is presented. We show that one reflectance measurement, made in the specular direction under specific conditions, allows the accurate calculation of the shape of the roughness histogram. As a theoretical background, we use modified expressions from Kirchhoff theory for surface scattering. To illustrate our method, we present experimental results obtained with surfaces having a multimode histogram, which means having several different populations with distinct peaks. For these surfaces, we observe oscillations in the regularly decreasing reflectance (with decreasing wavelength) that are created by a partial interference phenomenon between the peaks. To our knowledge, this effect is presented for the first time in the literature. Our study demonstrates that some very useful information can be obtained in the infrared spectrum of metallic substrates, although they do not have any absorption band. We hope that our results help further the understanding of complex spectral data obtained on such scattering substrates covered with organic films.

Algorithms↗