Hyperspectral diffuse reflectance imaging for rapid, noncontact measurement of the optical properties of turbid materials

We present a method and technique of using hyperspectral diffuse reflectance for rapid determination of the optical properties of turbid media. A hyperspectral imaging system in line scanning mode was used to acquire spatial diffuse reflectance profiles from liquid phantoms made up of absorbing dyes and fat emulsion scatterers over the spectral range of 450-1000 nm instantaneously. The hyperspectral reflectance data were analyzed by using a steady-state diffusion approximation model for semi-infinite homogeneous media. A calibration procedure was developed to compensate the nonuniform instrument response of the imaging system, and a curve-fitting algorithm was used to extract absorption and reduced scattering coefficients (mua and mus', respectively) for the phantoms in the wavelength range from 530 to 900 nm. The hyperspectral imaging system gave good measures of mua and mus' for the phantoms with average fitting errors of 12% and 7%, respectively. The hyperspectral imaging technique is fast, noncontact, and easy to use, which makes it especially suitable for measurement of the optical properties of turbid liquid and solid foods.     

Evaluation of an Accurate Mass Approach for the Simultaneous Detection of Drug and Metabolite Distributions via Whole-Body Mass Spectrometric Imaging

In drug discovery and development, in vitro absorption and metabolism assays along with in vivo pharmacokinetic (PK), pharmacodynamic (PD), and toxicokinetic (TK) studies are used to evaluate a potential drug candidate. More recently, imaging mass spectrometry approaches have been successfully reported to aid in the preclinical assessment of drug candidates, resulting in the rapid and noteworthy acceptance of the technique in pharmaceutical research. Traditionally, drug distribution studies via mass spectrometric imaging (MSI) are performed as targeted MS/MS analyses, where the analytes of interest, drug and/or metabolite, are known before the imaging experiment is performed. The study presented here describes a whole-body mass spectrometric imaging (WB-MSI) approach using a hybrid MALDI-LTQ-Orbitrap-MS to detect the distribution of reserpine at 2 h post a 20 mg/kg oral dose. This study effectively demonstrates the utility of obtaining accurate mass measurements across a wide mass range combined with postprocessing tools to efficiently identify drug and metabolite distributions without the need for any a priori knowledge.     

Metastable monoclinic ZnMoO4: hydrothermal synthesis, optical properties and photocatalytic performance

Metastable monoclinic ZnMoO4 was successfully synthesized via a hydrothermal route with variation of reaction temperatures and time at pH value of 5.7. Systematic sample characterizations were carried out, including X-ray powder diffraction, scanning electron microscopy, Fourier transformed infrared spectra, UV-visible diffuse reflectance spectra, and photoluminescence spectra. The results show that all as-prepared ZnMoO4 samples were demonstrated to crystallize in a pure-phase of monoclinic wolframite structure. All samples were formed in plate-like morphology. Six IR active vibrational bands were observed in the wave number range of 400-900 cm(-1). The band gap of as-prepared ZnMoO4 was estimated to be 2.86 eV by Tauc equation. Photoluminescence measurement indicates that as-prepared ZnMoO4 exhibits a broad blue-green emission under excitation wavelength of 280 nm at room temperature. Photocatalytic activity of as-prepared ZnMoO4 was examined by monitoring the degradation of methyl orange dye in an aqueous solution under UV radiation of 365 nm. The as-prepared ZnMoO4 obtained at 180 degrees C for 40 h showed the best photocatalytic activity with completing degradation of MO in irradiation time of 120 min. Consequently, monoclinic ZnMoO4 proved to be an efficient near visible light photocatalyst.     

Spectral-reflectance reconstruction in the near-infrared region by use of conventional charge-coupled-device camera measurements

Our aim is to develop a method for obtaining the reflectance spectra of samples in the near-infrared (NIR) region (800-1,000 nm) by using a small number of measurements performed with a conventional CCD camera (multispectral imaging). We experimentally determined the spectral sensitivity of the CCD camera in the NIR range, used a method based on principal component analysis to reconstruct the spectral reflectance of the samples, and analyzed the number and shape of the filters that need tobe used to apply this method. Finally we obtained the reflectance spectra of a set of 30 spectral curves by numerical simulation. The small amount of errors in the spectral reconstruction shows the potential of this method for reconstructing spectral reflectances in the NIR range.     

Directional-hemispherical reflectance for spectralon by integration of its bidirectional reflectance

The directional-hemispherical reflectance is obtained for Spectralon, the material chosen for onboard radiometric calibration of the multiangle imaging spectroradiometer, at laser wavelengths of 442, 632.8, and 859.9 nm. With p- and s-polarized incident light and for an angle of incidence of 45 degrees , the bidirectional reflectance distribution function was measured over a polar angle range of 1-85 degrees and a range of azimuthal angles of 0-180 degrees in 10 degrees increments. The resultant directional-hemispherical reflectance is found by integration to be 1.00 ? 0.01 at 442 nm, 0.953 ? 0.01 at 632.8 nm, and 0.956 ? 0.01 at 859.9 nm. The experimental methodology and the data analysis are presented together with a full discussion of the primary experimental errors.     

Self-referencing substrates for optical interferometric biosensors

Optical interference is a powerful technique for monitoring surface topography or refractive index changes in a thin film layer. Reflectance spectroscopy provides label-free biosensing capability by monitoring small variations in interference signature resulting from optical path length changes from surface-adsorbed biomolecules. Spectral reflectance data can be acquired either by broad wavelength illumination and spectroscopy at a single point, thus necessitating scanning, or by varying the wavelength of illumination and imaging the reflected intensity allowing for acquisition of a spectral image of a large field of view simultaneously. In imaging modalities, intensity fluctuations of the illuminating light source couple into the detected signal, increasing the noise in measured surface profiles. This article introduces a simple technique for eliminating the effects of illumination light power fluctuations by fabricating on-substrate self-reference regions to measure and normalize for the incident intensity, simplifying the overall platform for reflection or transmission-based imaging biosensors. Experimental results demonstrate that the sensitivity performance using self-referencing is equivalent or better than an optimized system with an external reference.     

Effect of spectral band numbers on the retrieval of water column and bottom properties from ocean color data

Using an optimization technique, we derived subsurface properties of coastal and oceanic waters from measured remote-sensing reflectance spectra. These data included both optically deep and shallow environments. The measured reflectance covered a spectral range from 400 to 800 nm. The inversions used data from each 5-, 10-, and 20-nm contiguous bands, including Sea-viewing Wide Field-of-view Sensor (SeaWiFS), moderate-resolution imaging spectrometer (MODIS), and a self-defined medium-resolution imaging spectrometer (MERIS) channels, respectively. This study is designed to evaluate the influence of spectral resolution and channel placement on the accuracy of remote-sensing retrievals and to provide guidance for future sensor design. From the results of this study, we found the following: (1) use of 10-nm-wide contiguous channels provides almost identical results as found for 5-nm contiguous channels; (2) use of 20-nm contiguous channels and MERIS provides comparable results with those with 5-nm contiguous channels for deep waters, but use of contiguous 20-nm channels perform better than MERIS for optically shallow waters; and (3) SeaWiFS or MODIS channels work fine for deep, clearer waters (total absorption coefficient at 440 nm < 0.3 m(-1)), but introduce more errors in bathymetry retrievals for optically shallow waters. The inclusion of the 645-nm MODIS land band in its channel set improves inversion returns for both deep and shallow waters.     

Alternative Method to Characterize Corn Grain by Means of Photoacoustic Spectroscopy

The application of photothermal (PT) techniques to obtain the optical and thermal properties of different materials has been widely reported in the literature. Among the PT techniques, photoacoustic spectroscopy stands out because this technique has been used to characterize different types of materials in solid, liquid, and gaseous phases, as well as homogeneous and inhomogeneous samples as biological materials which present great complexity in their structure. In particular, the seeds and corn kernels comprise different structural components such as endosperm, pericarp, embryo, and pedicel. The color attribute is very important in the grains because it gives information about the chemical composition and nutritional quality attributes which are important in consumer acceptance. In this investigation optical absorption spectra of corn grains were obtained by using photoacoustic spectroscopy in a wavelength range from 325 nm to 800 nm. Two varieties of corn grains were studied, establishing a complete block design at random for the measurements. From the obtained optical absorption spectra, the optical absorption coefficient ( $\beta $ ) was calculated as a function of the wavelength for each sample. A complementary study of the percentage of reflectance for these samples was carried out by using ultraviolet/visible spectrometry with an integrating sphere. The data were subjected to an analysis of the variance using software of the statistical analysis system. The results revealed significant differences ( $P\le 0.05$ ) between corn varieties in the range of 325 nm to 670 nm. The application of the photoacoustic spectroscopy technique as an alternative to conventional methods for the characterization of maize grain through an analysis of $\beta $ could be important for characterizing non-homogeneous materials like grains of corn, whose characterization is relevant in the food industry.     

Limitations of using Raman microscopy for the analysis of high-content-carbon-filled ethylene propylene diene monomer rubber

The effects of laser irradiation on changes to the surface chemistry and structure of a commercially available ethylene propylene diene monomer (EPDM) rubber sample after Raman microscopy analysis was investigated. The Raman measurements were carried out with different levels of laser power on the sample, ranging from 4.55 mW to 0.09 mW. The surface of the EPDM was analyzed before and after laser exposure using X-ray photoelectron spectroscopy (XPS) and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. The techniques have surface probe depths of approximately < or = 10 nm and 1 microm, respectively. Both sets of analysis show that ingredients of the blended EPDM rubber "bloom" to the surface as a result of local heating that takes place due to the absorption of laser by carbon black during the Raman analysis. Scanning electron microscopy (SEM) analysis was also performed on the Raman analyzed areas to visually illustrate the effects created due to laser light exposure (i.e., burning marks). The change in surface chemistry also occurs in regions a few millimeters from the exposed sites, indicating that the effect is quite long range. However, this phenomenon has no major influence, as far as XPS or ATR-FTIR results disclose, on the backbone structure of the rubber sample. The results indicate that precautions should be taken when analyzing complex blended polymer samples using Raman spectroscopy.     

Non-destructive evaluation of composite materials using a capacitive imaging technique

This paper describes the application of the capacitive imaging technique to the inspection of composite materials. The fundamental theory of the capacitive imaging technique was briefly described. Experiments using prototype capacitive imaging probes were also carried out. The proof-of-concept results indicated that the capacitive imaging technique could be used to detect cracks and delaminations in the glass fibre composite, defects in the aluminium core through the glass fibre face as well as surface features on the carbon fibre specimens.     

Structural and optical properties of thermally evaporated 1,4,8,11,15,18,22,25-octahexylphthalocyanine thin films

Metal-free 1,4,8,11,15,18,22,25-octahexylphthalocyanine was prepared directly by the cyclotetramerization of 3,6-dihexylphthalonitrile using lithium butoxide in butanol. Thin films of the material were deposited on glass substrates by the thermal evaporation technique. The structure of the films was found to be in the form, and showed a strong peak indicating preferential orientation. The surface morphology of the thin films was investigated by atomic force microscopy and showed that the molecules of 1,4,8,11,15,18,22,25-octahexylphthalocyanine grow in stacks of parallel rows. The spectrophotometric measurements of transmittance and reflectance were carried out in the wavelength range 190–3000 nm. The refractive index, n, and absorption index, k, were found to be independent of annealing at 373 K. The B band absorption occurred at 356 nm, and the Q band showed a doublet at 667 and 739 nm. Other optical parameters, such as absorption coefficient and optical dielectric constant ε, were determined.     

Photonic-crystal light-emitting diodes on p-type GaAs substrates for optical communications

Oxide-confined photonic-crystal (PhC) light-emitting diodes (LEDs) on p-type GaAs substrate in the 830 nm range are reported. The device consists of a bottom distributed Bragg reflector (DBR), quantum wells (QWs), and a top DBR, with a photonic-crystal structure formed within the n-type ohmic contact ring for light extraction. The etching depth of the PhC holes is 17-pair out of the 22-pair top DBR being etched off. The internally reflected spontaneous light emission can be extracted out of PhC holes because of lower reflectance within those areas. High-resolution micrographic imaging studies indicate that the device emits light mainly through the photonic-crystal holes and it is suitable for optical communications.     

Spectral reflectance and responsivity of Ge- and InGaAs-photodiodes in the near-infrared: measurement and model

The spectral reflectance and responsivity of Ge- and InGaAs-photodiodes at (nearly) normal and oblique incidence (45 degrees) were investigated. The derived data allow a calculation of the photodiodes responsivities for any incident angle. The measurements were carried out with s- and p-polarized radiation in the wavelength range from 1260 to 1640 nm. The spectral reflectance of the photodiodes was modeled by using the matrix approach developed for thin-film optical assemblies. The comparison between the calculated and measured reflectance shows a difference of less than 2% for the Ge-photodiode. For the InGaAs-photodiode, the differences between measured and calculated reflectance are larger, i.e., up to 6% for wavelengths between 1380 and 1580 nm. Despite the larger differences between calculated and measured spectral reflectances for the InGaAs-photodiode, the difference between calculated and measured spectral responsivity is even smaller for the InGaAs-photodiode than for the Ge-photodiode, i.e., < or =1.2% for the InGaAs-photodiode compared to < or =2.2% for the Ge-photodiode. This is because the difference in responsivity is strongly correlated to the absolute spectral reflectance level, which is much lower for the InGaAs-photodiode. This observation also shows the importance of having small reflectances, i.e., appropriate antireflection coatings for the photodiodes. The relative standard uncertainty associated with the modeled spectral responsivity is about 2.2% for the Ge-photodiode and about 1.2% for the InGaAs-photodiode for any incident angle over the whole spectral range measured. The data obtained for the photodiodes allow the calculation of the spectral responsivity of Ge- and InGaAs-trap detectors and the comparison with experimental results.     

多波段伪装隐身涂层织物的制备研究与应用

采用着色颜料、红外低发射率填料、水性聚氨酯树脂等制备水性多波段伪装涂料,采用刮涂工艺,制备可见光/近红外/热红外多波段伪装涂层织物。通过双波段发射率测量仪、光谱反射率测试仪、光泽度仪等测试手段对涂层的红外发射率、光谱反射率、镜面光泽度等性能进行了表征,此外还对涂层的理化及环境性能进行了测试。结果表明:涂层的颜色满足《GJB 1082—1991伪装网用颜色》的要求,近红外光谱反射特性在380~1100nm范围内与应用背景基本实现了"同色同谱",不同颜色斑块的发射率梯度在0.13以上,在红外成像下能够形成有效的梯度分割,与应用背景具有较好的融合效果,具有可见光/近红外/热红外隐身性能,各项指标均达到了实用要求。     

利用WDM光纤耦合器的光纤光栅传感解调技术

根据 WDM 光纤耦合器波长解调方案的工作原理、偏振特性以及影响系统波长分辨力的因素,提出一种改进的利用 WDM 光纤耦合器的光纤光栅传感解调技术。该技术在原技术的基础上,采用偏振控制器控制入射光偏振状态,提高了解调的精度和稳定性。对 WDM 光纤耦合器的多次波长扫描结果表明,采用偏振控制器后,其波长误差可减小到 5pm 左右。实验采用 1540/1560nm的 WDM 光纤耦合器对单点光纤光栅应变传感器进行静态解调,结果表明:按此技术开发的解调系统具有 0.01nm 波长分辨力和 10nm 的波长线性解调范围。     

Interest of broadband optical monitoring for thin-film filter manufacturing

Broadband optical monitoring for thin-film filter manufacturing is more and more developed thanks to better performances of spectrometers with array detectors. We compare this optical monitoring with turning point monitoring and quartz monitoring of different designs. The sensitivity to thickness errors and to refractive index errors is evaluated. We show that real time determination of deposited thickness is a valuable criterion. We also present our experimental setup of transmittance and reflectance broadband optical monitoring. The use of a 400-1000 nm range combined with a signal-to-noise ratio of ~2500 in transmittance and 1000 in reflectance permits us to expect the manufacturing of high-performance non-quarter-wave designs. A first manufacturing of an 18-layer non-quarter-wave high-pass filter is provided.     

Simultaneous measurement of changes in light absorption due to the reduction of cytochrome c oxidase and light scattering in rat brains during loss of tissue viability

We performed the simultaneous measurement of intrinsic optical signals (IOSs) related to metabolic activity and cellular and subcellular morphological characteristics, i.e., light scattering for a rat global ischemic brain model made by rapidly removing blood by saline infusion. The signals were measured on the basis of multiwavelength diffuse reflectances in which 605 and 830 nm were used to detect the IOSs that are thought to be dominantly affected by redox changes of heme aa(3) and CuA in cytochrome c oxidase (CcO), respectively. For measuring the scattering signal, the wavelength that was found to be most insensitive to the absorption changes, e.g., approximately 620 nm, was used. The measurements suggested that an increase in the absorption due to reduction of heme aa(3) occurred soon after blood clearance, and this was followed by a large triphasic change in light scattering, during which time a decrease in the absorption due to reduction of CuA occurred. Through the triphasic scattering change, scattering signals increased by 5.2 +/- 1.5% (n = 5), and the increase in light scattering showed significant correlation with both the reflectance intensity changes at 605 and 830 nm. This suggests that morphological changes in cells correlate with reductions of heme aa(3) and CuA. Histological analysis of tissue after the triphasic scattering change showed no alteration in either the nuclei or the cytoskeleton, but electron microscopic observation revealed deformed, enlarged mitochondria and expanded dendrites. These findings suggest that the simultaneous measurement of absorption signals related to the redox changes in the CcO and the scattering signal is useful for monitoring tissue viability in the brain.     

Nanoparticle-assisted laser desorption/ionization based mass imaging with cellular resolution

Today, two-dimensional mass spectrometry analysis of biological tissues by means of a technique called mass imaging, mass spectrometry imaging (MSI), or imaging mass spectrometry (IMS) has found application in investigating the distribution of moleculesMSI with matrix-assisted laser desorption/ionization (MALDI) and secondary ion MS (SIMS). However, the size of the matrix crystal and the migration of analytes can decrease the spatial resolution in MALDI, and SIMS can only ionize compounds with relatively low molecular weights. To overcome these problems, we developed a nanoparticle-assisted laser desorption/ionization (nano-PALDI)-based MSI. We used nano-PALDI MSI to visualize lipids and peptides at a resolution of 15 microm in mammalian tissues.     

Model for the interpretation of hyperspectral remote-sensing reflectance

Remote-sensing reflectance is easier to interpret for the open ocean than for coastal regions because the optical signals are highly coupled to the phytoplankton (e.g., chlorophyll) concentrations. For estuarine or coastal waters, variable terrigenous colored dissolved organic matter (CDOM), suspended sediments, and bottom reflectance, all factors that do not covary with the pigment concentration, confound data interpretation. In this research, remote-sensing reflectance models are suggested for coastal waters, to which contributions that are due to bottom reflectance, CDOM fluorescence, and water Raman scattering are included. Through the use of two parameters to model the combination of the backscattering coefficient and the Q factor, excellent agreement was achieved between the measured and modeled remote-sensing reflectance for waters from the West Florida Shelf to the Mississippi River plume. These waters cover a range of chlorophyll of 0.2-40 mg/m(3) and gelbstoff absorption at 440 nm from 0.02-0.4 m(-1). Data with a spectral resolution of 10 nm or better, which is consistent with that provided by the airborne visible and infrared imaging spectrometer (AVIRIS) and spacecraft spectrometers, were used in the model evaluation.     

Imaging reflectometry in situ

An innovative method of in situ real-time optical monitoring of thin film deposition and etching is presented. In this technique, intensity maps of a thin film corresponding to a series of wavelengths selected by a monochromator (300-800 nm) are recorded by a CCD camera. From the maps the reflectance spectra at individual points of the sample surface can be extracted. By fitting the reflectance spectra to the theoretical ones, the maps of a thin film morphology (including optical parameters) and their temporal development during technological processes can be obtained. The method was tested by in situ observation of the growth of silicon nitride and silicon oxide thin films prepared by ion beam sputtering and by the monitoring of etching of thermally grown SiO(2) thin films.